Add the Babel routing protocol (RFC 6126)

This patch implements the IPv6 subset of the Babel routing protocol.
Based on the patch from Toke Hoiland-Jorgensen, with some heavy
modifications and bugfixes.

Thanks to Toke Hoiland-Jorgensen for the original patch.

19 files changed, 3767 insertions, 10 deletions

diff --git a/configure.in b/configure.in
index b9220a1d..16a0b414 100644
--- a/configure.in
+++ b/configure.in
@@ -206,6 +206,9 @@ fi
 AC_SUBST(iproutedir)
 
 all_protocols="$proto_bfd bgp ospf pipe $proto_radv rip static"
+if test "$ip" = ipv6 ; then
+   all_protocols="$all_protocols babel"
+fi
 all_protocols=`echo $all_protocols | sed 's/ /,/g'`
 
 if test "$with_protocols" = all ; then
diff --git a/doc/bird.sgml b/doc/bird.sgml
index 1a5fbaff..6c6ff3db 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -1380,6 +1380,102 @@ corresponding protocol sections.
 
 <chapt>Protocols
 
+<sect>Babel
+
+<sect1>Introduction
+
+<p>The Babel protocol (RFC6126) is a loop-avoiding distance-vector routing
+protocol that is robust and efficient both in ordinary wired networks and in
+wireless mesh networks. Babel is conceptually very simple in its operation and
+"just works" in its default configuration, though some configuration is possible
+and in some cases desirable.
+
+<p>While the Babel protocol is dual stack (i.e., can carry both IPv4 and IPv6
+routes over the same IPv6 transport), BIRD presently implements only the IPv6
+subset of the protocol. No Babel extensions are implemented, but the BIRD
+implementation can coexist with implementations using the extensions (and will
+just ignore extension messages).
+
+<p>The Babel protocol implementation in BIRD is currently in alpha stage.
+
+<sect1>Configuration
+
+<p>Babel supports no global configuration options apart from those common to all
+other protocols, but supports the following per-interface configuration options:
+
+<code>
+protocol babel [<name>] {
+	interface <interface pattern> {
+		type <wired|wireless>;
+		rxcost <number>;
+		hello interval <number>;
+		update interval <number>;
+		port <number>;
+		tx class|dscp <number>;
+		tx priority <number>;
+		rx buffer <number>;
+		tx length <number>;
+		check link <switch>;
+	};
+}
+</code>
+
+<descrip>
+      <tag>type wired|wireless </tag>
+      This option specifies the interface type: Wired or wireless. Wired
+      interfaces are considered more reliable, and so the default hello
+      interval is higher, and a neighbour is considered unreachable after only
+      a small number of "hello" packets are lost. On wireless interfaces,
+      hello packets are sent more often, and the ETX link quality estimation
+      technique is used to compute the metrics of routes discovered over this
+      interface. This technique will gradually degrade the metric of routes
+      when packets are lost rather than the more binary up/down mechanism of
+      wired type links. Default: <cf/wired/.
+
+      <tag>rxcost <m/num/</tag>
+      This specifies the RX cost of the interface. The route metrics will be
+      computed from this value with a mechanism determined by the interface
+      <cf/type/. Default: 96 for wired interfaces, 256 for wireless.
+
+      <tag>hello interval <m/num/</tag>
+      Interval at which periodic "hello" messages are sent on this interface,
+      in seconds. Default: 4 seconds.
+
+      <tag>update interval <m/num/</tag>
+      Interval at which periodic (full) updates are sent. Default: 4 times the
+      hello interval.
+
+      <tag>port <m/number/</tag>
+      This option selects an UDP port to operate on. The default is to operate
+      on port 6696 as specified in the Babel RFC.
+
+      <tag>tx class|dscp|priority <m/number/</tag>
+      These options specify the ToS/DiffServ/Traffic class/Priority of the
+      outgoing Babel packets. See <ref id="dsc-prio" name="tx class"> common
+      option for detailed description.
+
+      <tag>rx buffer <m/number/</tag>
+      This option specifies the size of buffers used for packet processing.
+      The buffer size should be bigger than maximal size of received packets.
+      The default value is the interface MTU, and the value will be clamped to a
+      minimum of 512 bytes + IP packet overhead.
+
+      <tag>tx length <m/number/</tag>
+      This option specifies the maximum length of generated Babel packets. To
+      avoid IP fragmentation, it should not exceed the interface MTU value.
+      The default value is the interface MTU value, and the value will be
+      clamped to a minimum of 512 bytes + IP packet overhead.
+
+      <tag>check link <m/switch/</tag>
+      If set, the hardware link state (as reported by OS) is taken into
+      consideration. When the link disappears (e.g. an ethernet cable is
+      unplugged), neighbors are immediately considered unreachable and all
+      routes received from them are withdrawn. It is possible that some
+      hardware drivers or platforms do not implement this feature. Default:
+      yes.
+</descrip>
+
+
 <sect><label id="sect-bfd">BFD
 
 <sect1>Introduction
diff --git a/doc/reply_codes b/doc/reply_codes
index 79a7eb92..3a7f2c90 100644
--- a/doc/reply_codes
+++ b/doc/reply_codes
@@ -57,6 +57,9 @@ Reply codes of BIRD command-line interface
 1020	Show BFD sessions
 1021	Show RIP interface
 1022	Show RIP neighbors
+1023	Show Babel interfaces
+1024	Show Babel neighbors
+1025	Show Babel entries
 
 8000	Reply too long
 8001	Route not found
diff --git a/lib/birdlib.h b/lib/birdlib.h
index 16f437ef..904544cb 100644
--- a/lib/birdlib.h
+++ b/lib/birdlib.h
@@ -60,6 +60,7 @@
 
 #define NORET __attribute__((noreturn))
 #define UNUSED __attribute__((unused))
+#define PACKED __attribute__((packed))
 
 
 /* Microsecond time */
diff --git a/lib/bitops.h b/lib/bitops.h
index c0ad1a70..ce13732a 100644
--- a/lib/bitops.h
+++ b/lib/bitops.h
@@ -25,5 +25,6 @@ u32 u32_log2(u32 v);
 
 static inline u32 u32_hash(u32 v) { return v * 2902958171u; }
 
-#endif
+static inline u8 u32_popcount(u32 v) { return __builtin_popcount(v); }
 
+#endif
diff --git a/lib/ip.h b/lib/ip.h
index 5389c44a..298b72a7 100644
--- a/lib/ip.h
+++ b/lib/ip.h
@@ -26,6 +26,7 @@
 #define IP6_OSPF_ALL_ROUTERS	ipa_build6(0xFF020000, 0, 0, 5)
 #define IP6_OSPF_DES_ROUTERS	ipa_build6(0xFF020000, 0, 0, 6)
 #define IP6_RIP_ROUTERS		ipa_build6(0xFF020000, 0, 0, 9)
+#define IP6_BABEL_ROUTERS	ipa_build6(0xFF020000, 0, 0, 0x00010006)
 
 #define IP4_NONE		_MI4(0)
 #define IP6_NONE		_MI6(0,0,0,0)
diff --git a/lib/printf.c b/lib/printf.c
index e4cc3006..a067fe98 100644
--- a/lib/printf.c
+++ b/lib/printf.c
@@ -124,6 +124,7 @@ static char * number(char * str, long num, int base, int size, int precision,
  * width is automatically replaced by standard IP address width which
  * depends on whether we use IPv4 or IPv6; |%#I| gives hexadecimal format),
  * |%R| for Router / Network ID (u32 value printed as IPv4 address)
+ * |%lR| for 64bit Router / Network ID (u64 value printed as eight :-separated octets)
  * and |%m| resp. |%M| for error messages (uses strerror() to translate @errno code to
  * message text). On the other hand, it doesn't support floating
  * point numbers.
@@ -137,9 +138,10 @@ int bvsnprintf(char *buf, int size, const char *fmt, va_list args)
 	unsigned long num;
 	int i, base;
 	u32 x;
+	u64 X;
 	char *str, *start;
 	const char *s;
-	char ipbuf[STD_ADDRESS_P_LENGTH+1];
+	char ipbuf[MAX(STD_ADDRESS_P_LENGTH,ROUTER_ID_64_LENGTH)+1];
 	struct iface *iface;
 
 	int flags;		/* flags to number() */
@@ -309,12 +311,27 @@ int bvsnprintf(char *buf, int size, const char *fmt, va_list args)
 
 		/* Router/Network ID - essentially IPv4 address in u32 value */
 		case 'R':
-			x = va_arg(args, u32);
-			bsprintf(ipbuf, "%d.%d.%d.%d",
-				 ((x >> 24) & 0xff),
-				 ((x >> 16) & 0xff),
-				 ((x >> 8) & 0xff),
-				 (x & 0xff));
+			if(qualifier == 'l') {
+				X = va_arg(args, u64);
+				bsprintf(ipbuf, "%02x:%02x:%02x:%02x:%02x:%02x:%02x:%02x",
+					((X >> 56) & 0xff),
+					((X >> 48) & 0xff),
+					((X >> 40) & 0xff),
+					((X >> 32) & 0xff),
+					((X >> 24) & 0xff),
+					((X >> 16) & 0xff),
+					((X >> 8) & 0xff),
+					(X & 0xff));
+			}
+			else
+			{
+				x = va_arg(args, u32);
+				bsprintf(ipbuf, "%d.%d.%d.%d",
+					((x >> 24) & 0xff),
+					((x >> 16) & 0xff),
+					((x >> 8) & 0xff),
+					(x & 0xff));
+			}
 			s = ipbuf;
 			goto str;
 
diff --git a/lib/string.h b/lib/string.h
index 0f249d37..9af49b9e 100644
--- a/lib/string.h
+++ b/lib/string.h
@@ -30,4 +30,6 @@ static inline char *xbasename(const char *str)
   return s ? s+1 : (char *) str;
 }
 
+#define ROUTER_ID_64_LENGTH 23
+
 #endif
diff --git a/nest/proto.c b/nest/proto.c
index 436377f1..3e97e9da 100644
--- a/nest/proto.c
+++ b/nest/proto.c
@@ -919,6 +919,9 @@ protos_build(void)
   proto_build(&proto_bfd);
   bfd_init_all();
 #endif
+#ifdef CONFIG_BABEL
+  proto_build(&proto_babel);
+#endif
 
   proto_pool = rp_new(&root_pool, "Protocols");
   proto_flush_event = ev_new(proto_pool);
diff --git a/nest/protocol.h b/nest/protocol.h
index 8c49154f..ec787355 100644
--- a/nest/protocol.h
+++ b/nest/protocol.h
@@ -76,7 +76,7 @@ void protos_dump_all(void);
 
 extern struct protocol
   proto_device, proto_radv, proto_rip, proto_static,
-  proto_ospf, proto_pipe, proto_bgp, proto_bfd;
+  proto_ospf, proto_pipe, proto_bgp, proto_bfd, proto_babel;
 
 /*
  *	Routing Protocol Instance
diff --git a/nest/route.h b/nest/route.h
index 9368808f..3969db6b 100644
--- a/nest/route.h
+++ b/nest/route.h
@@ -220,6 +220,12 @@ typedef struct rte {
       u8 suppressed;			/* Used for deterministic MED comparison */
     } bgp;
 #endif
+#ifdef CONFIG_BABEL
+    struct {
+      u16 metric;			/* Babel metric */
+      u64 router_id;			/* Babel router id */
+    } babel;
+#endif
     struct {				/* Routes generated by krt sync (both temporary and inherited ones) */
       s8 src;				/* Alleged route source (see krt.h) */
       u8 proto;				/* Kernel source protocol ID */
@@ -374,6 +380,7 @@ typedef struct rta {
 #define RTS_OSPF_EXT2 10		/* OSPF external route type 2 */
 #define RTS_BGP 11			/* BGP route */
 #define RTS_PIPE 12			/* Inter-table wormhole */
+#define RTS_BABEL 13			/* Babel route */
 
 #define RTC_UNICAST 0
 #define RTC_BROADCAST 1
@@ -422,7 +429,8 @@ typedef struct eattr {
 #define EAP_RIP 2			/* RIP */
 #define EAP_OSPF 3			/* OSPF */
 #define EAP_KRT 4			/* Kernel route attributes */
-#define EAP_MAX 5
+#define EAP_BABEL 5			/* Babel attributes */
+#define EAP_MAX 6
 
 #define EA_CODE(proto,id) (((proto) << 8) | (id))
 #define EA_PROTO(ea) ((ea) >> 8)
@@ -547,6 +555,7 @@ extern struct protocol *attr_class_to_protocol[EAP_MAX];
 #define DEF_PREF_DIRECT	    	240	/* Directly connected */
 #define DEF_PREF_STATIC		200	/* Static route */
 #define DEF_PREF_OSPF		150	/* OSPF intra-area, inter-area and type 1 external routes */
+#define DEF_PREF_BABEL		130	/* Babel */
 #define DEF_PREF_RIP		120	/* RIP */
 #define DEF_PREF_BGP		100	/* BGP */
 #define DEF_PREF_PIPE		70	/* Routes piped from other tables */
diff --git a/proto/Doc b/proto/Doc
index 7863472f..04c25bc0 100644
--- a/proto/Doc
+++ b/proto/Doc
@@ -1,4 +1,5 @@
 H Protocols
+C babel
 C bfd
 C bgp
 C ospf
diff --git a/proto/babel/Doc b/proto/babel/Doc
new file mode 100644
index 00000000..2480239e
--- /dev/null
+++ b/proto/babel/Doc
@@ -0,0 +1,2 @@
+S babel.c
+S packet.c
diff --git a/proto/babel/Makefile b/proto/babel/Makefile
new file mode 100644
index 00000000..400ffbac
--- /dev/null
+++ b/proto/babel/Makefile
@@ -0,0 +1,5 @@
+source=babel.c packets.c
+root-rel=../../
+dir-name=proto/babel
+
+include ../../Rules
diff --git a/proto/babel/babel.c b/proto/babel/babel.c
new file mode 100644
index 00000000..8e104d60
--- /dev/null
+++ b/proto/babel/babel.c
@@ -0,0 +1,2055 @@
+/*
+ *	BIRD -- The Babel protocol
+ *
+ *	Copyright (c) 2015--2016 Toke Hoiland-Jorgensen
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ *
+ *	This file contains the main routines for handling and sending TLVs, as
+ *	well as timers and interaction with the nest.
+ */
+
+/**
+ * DOC: The Babel protocol
+ *
+ * Babel (RFC6126) is a loop-avoiding distance-vector routing protocol that is
+ * robust and efficient both in ordinary wired networks and in wireless mesh
+ * networks.
+ *
+ * The Babel protocol keeps state for each neighbour in a &babel_neighbor
+ * struct, tracking received Hello and I Heard You (IHU) messages. A
+ * &babel_interface struct keeps hello and update times for each interface, and
+ * a separate hello seqno is maintained for each interface.
+ *
+ * For each prefix, Babel keeps track of both the possible routes (with next hop
+ * and router IDs), as well as the feasibility distance for each prefix and
+ * router id. The prefix itself is tracked in a &babel_entry struct, while the
+ * possible routes for the prefix are tracked as &babel_route entries and the
+ * feasibility distance is maintained through &babel_source structures.
+ *
+ * The main route selection is done in babel_select_route(). This is called when
+ * an entry is updated by receiving updates from the network or when modified by
+ * internal timers. It performs feasibility checks on the available routes for
+ * the prefix and selects the one with the lowest metric to be announced to the
+ * core.
+ */
+
+#include <stdlib.h>
+#include "babel.h"
+
+
+#define OUR_ROUTE(r) (r->neigh == NULL)
+
+/*
+ * Is one number greater or equal than another mod 2^16? This is based on the
+ * definition of serial number space in RFC 1982. Note that arguments are of
+ * uint type to avoid integer promotion to signed integer.
+ */
+static inline int ge_mod64k(uint a, uint b)
+{ return (u16)(a - b) < 0x8000; }
+
+static void babel_dump_entry(struct babel_entry *e);
+static void babel_dump_route(struct babel_route *r);
+static void babel_select_route(struct babel_entry *e);
+static void babel_send_route_request(struct babel_entry *e, struct babel_neighbor *n);
+static void babel_send_wildcard_request(struct babel_iface *ifa);
+static int  babel_cache_seqno_request(struct babel_proto *p, ip_addr prefix, u8 plen,
+			       u64 router_id, u16 seqno);
+static void babel_trigger_iface_update(struct babel_iface *ifa);
+static void babel_trigger_update(struct babel_proto *p);
+static void babel_send_seqno_request(struct babel_entry *e);
+static inline void babel_kick_timer(struct babel_proto *p);
+static inline void babel_iface_kick_timer(struct babel_iface *ifa);
+
+
+/*
+ *	Functions to maintain data structures
+ */
+
+static void
+babel_init_entry(struct fib_node *n)
+{
+  struct babel_entry *e = (void *) n;
+  e->proto = NULL;
+  e->selected_in = NULL;
+  e->selected_out = NULL;
+  e->updated = now;
+  init_list(&e->sources);
+  init_list(&e->routes);
+}
+
+static inline struct babel_entry *
+babel_find_entry(struct babel_proto *p, ip_addr prefix, u8 plen)
+{
+  return fib_find(&p->rtable, &prefix, plen);
+}
+
+static struct babel_entry *
+babel_get_entry(struct babel_proto *p, ip_addr prefix, u8 plen)
+{
+  struct babel_entry *e = fib_get(&p->rtable, &prefix, plen);
+  e->proto = p;
+  return e;
+}
+
+static struct babel_source *
+babel_find_source(struct babel_entry *e, u64 router_id)
+{
+  struct babel_source *s;
+
+  WALK_LIST(s, e->sources)
+    if (s->router_id == router_id)
+      return s;
+
+  return NULL;
+}
+
+static struct babel_source *
+babel_get_source(struct babel_entry *e, u64 router_id)
+{
+  struct babel_proto *p = e->proto;
+  struct babel_source *s = babel_find_source(e, router_id);
+
+  if (s)
+    return s;
+
+  s = sl_alloc(p->source_slab);
+  s->router_id = router_id;
+  s->expires = now + BABEL_GARBAGE_INTERVAL;
+  s->seqno = 0;
+  s->metric = BABEL_INFINITY;
+  add_tail(&e->sources, NODE s);
+
+  return s;
+}
+
+static void
+babel_expire_sources(struct babel_entry *e)
+{
+  struct babel_proto *p = e->proto;
+  struct babel_source *n, *nx;
+
+  WALK_LIST_DELSAFE(n, nx, e->sources)
+  {
+    if (n->expires && n->expires <= now)
+    {
+      rem_node(NODE n);
+      sl_free(p->source_slab, n);
+    }
+  }
+}
+
+static struct babel_route *
+babel_find_route(struct babel_entry *e, struct babel_neighbor *n)
+{
+  struct babel_route *r;
+
+  WALK_LIST(r, e->routes)
+    if (r->neigh == n)
+      return r;
+
+  return NULL;
+}
+
+static struct babel_route *
+babel_get_route(struct babel_entry *e, struct babel_neighbor *nbr)
+{
+  struct babel_proto *p = e->proto;
+  struct babel_route *r = babel_find_route(e, nbr);
+
+  if (r)
+    return r;
+
+  r = sl_alloc(p->route_slab);
+  memset(r, 0, sizeof(*r));
+  r->e = e;
+  add_tail(&e->routes, NODE r);
+
+  if (nbr)
+  {
+    r->neigh = nbr;
+    r->expires = now + BABEL_GARBAGE_INTERVAL;
+    add_tail(&nbr->routes, NODE &r->neigh_route);
+  }
+
+  return r;
+}
+
+static void
+babel_flush_route(struct babel_route *r)
+{
+  struct babel_proto *p = r->e->proto;
+
+  DBG("Babel: Flush route %I/%d router_id %lR neigh %I\n",
+      r->e->n.prefix, r->e->n.pxlen, r->router_id, r->neigh ? r->neigh->addr : IPA_NONE);
+
+  rem_node(NODE r);
+
+  if (r->neigh)
+    rem_node(&r->neigh_route);
+
+  if (r->e->selected_in == r)
+    r->e->selected_in = NULL;
+
+  if (r->e->selected_out == r)
+    r->e->selected_out = NULL;
+
+  sl_free(p->route_slab, r);
+}
+
+static void
+babel_expire_route(struct babel_route *r)
+{
+  struct babel_proto *p = r->e->proto;
+  struct babel_entry *e = r->e;
+
+  TRACE(D_EVENTS, "Route expiry timer for %I/%d router-id %lR fired",
+	e->n.prefix, e->n.pxlen, r->router_id);
+
+  if (r->metric < BABEL_INFINITY)
+  {
+    r->metric = BABEL_INFINITY;
+    r->expires = now + r->expiry_interval;
+  }
+  else
+  {
+    babel_flush_route(r);
+  }
+}
+
+static void
+babel_refresh_route(struct babel_route *r)
+{
+  if (!OUR_ROUTE(r) && (r == r->e->selected_in))
+    babel_send_route_request(r->e, r->neigh);
+
+  r->refresh_time = 0;
+}
+
+static void
+babel_expire_routes(struct babel_proto *p)
+{
+  struct babel_entry *e;
+  struct babel_route *r, *rx;
+  struct fib_iterator fit;
+
+  FIB_ITERATE_INIT(&fit, &p->rtable);
+
+loop:
+  FIB_ITERATE_START(&p->rtable, &fit, n)
+  {
+    e = (struct babel_entry *) n;
+    int changed = 0;
+
+    WALK_LIST_DELSAFE(r, rx, e->routes)
+    {
+      if (r->refresh_time && r->refresh_time <= now)
+	babel_refresh_route(r);
+
+      if (r->expires && r->expires <= now)
+      {
+	babel_expire_route(r);
+	changed = 1;
+      }
+    }
+
+    if (changed)
+    {
+      /*
+       * We have to restart the iteration because there may be a cascade of
+       * synchronous events babel_select_route() -> nest table change ->
+       * babel_rt_notify() -> p->rtable change, invalidating hidden variables.
+       */
+
+      FIB_ITERATE_PUT(&fit, n);
+      babel_select_route(e);
+      goto loop;
+    }
+
+    babel_expire_sources(e);
+
+    /* Remove empty entries */
+    if (EMPTY_LIST(e->sources) && EMPTY_LIST(e->routes))
+    {
+      FIB_ITERATE_PUT(&fit, n);
+      fib_delete(&p->rtable, e);
+      goto loop;
+    }
+  }
+  FIB_ITERATE_END(n);
+}
+
+static struct babel_neighbor *
+babel_find_neighbor(struct babel_iface *ifa, ip_addr addr)
+{
+  struct babel_neighbor *nbr;
+
+  WALK_LIST(nbr, ifa->neigh_list)
+    if (ipa_equal(nbr->addr, addr))
+      return nbr;
+
+  return NULL;
+}
+
+static struct babel_neighbor *
+babel_get_neighbor(struct babel_iface *ifa, ip_addr addr)
+{
+  struct babel_neighbor *nbr = babel_find_neighbor(ifa, addr);
+
+  if (nbr)
+    return nbr;
+
+  nbr = mb_allocz(ifa->pool, sizeof(struct babel_neighbor));
+  nbr->ifa = ifa;
+  nbr->addr = addr;
+  nbr->txcost = BABEL_INFINITY;
+  init_list(&nbr->routes);
+  add_tail(&ifa->neigh_list, NODE nbr);
+
+  return nbr;
+}
+
+static void
+babel_flush_neighbor(struct babel_neighbor *nbr)
+{
+  struct babel_proto *p = nbr->ifa->proto;
+  node *n;
+
+  TRACE(D_EVENTS, "Flushing neighbor %I", nbr->addr);
+
+  WALK_LIST_FIRST(n, nbr->routes)
+  {
+    struct babel_route *r = SKIP_BACK(struct babel_route, neigh_route, n);
+    struct babel_entry *e = r->e;
+    int selected = (r == e->selected_in);
+
+    babel_flush_route(r);
+
+    if (selected)
+      babel_select_route(e);
+  }
+
+  rem_node(NODE nbr);
+  mb_free(nbr);
+}
+
+static void
+babel_expire_ihu(struct babel_neighbor *nbr)
+{
+  nbr->txcost = BABEL_INFINITY;
+}
+
+static void
+babel_expire_hello(struct babel_neighbor *nbr)
+{
+  nbr->hello_map <<= 1;
+
+  if (nbr->hello_cnt < 16)
+    nbr->hello_cnt++;
+
+  if (!nbr->hello_map)
+    babel_flush_neighbor(nbr);
+}
+
+static void
+babel_expire_neighbors(struct babel_proto *p)
+{
+  struct babel_iface *ifa;
+  struct babel_neighbor *nbr, *nbx;
+
+  WALK_LIST(ifa, p->interfaces)
+  {
+    WALK_LIST_DELSAFE(nbr, nbx, ifa->neigh_list)
+    {
+      if (nbr->ihu_expiry && nbr->ihu_expiry <= now)
+        babel_expire_ihu(nbr);
+
+      if (nbr->hello_expiry && nbr->hello_expiry <= now)
+        babel_expire_hello(nbr);
+    }
+  }
+}
+
+
+/*
+ *	Best route selection
+ */
+
+/*
+ * From the RFC (section 3.5.1):
+ *
+ * a route advertisement carrying the quintuple (prefix, plen, router-id, seqno,
+ * metric) is feasible if one of the following conditions holds:
+ *
+ * - metric is infinite; or
+ *
+ * - no entry exists in the source table indexed by (id, prefix, plen); or
+ *
+ * - an entry (prefix, plen, router-id, seqno', metric') exists in the source
+ *   table, and either
+ *   - seqno' < seqno or
+ *   - seqno = seqno' and metric < metric'.
+ */
+static inline int
+babel_is_feasible(struct babel_source *s, u16 seqno, u16 metric)
+{
+  return !s ||
+    (metric == BABEL_INFINITY) ||
+    (seqno > s->seqno) ||
+    ((seqno == s->seqno) && (metric < s->metric));
+}
+
+static u16
+babel_compute_rxcost(struct babel_neighbor *n)
+{
+  struct babel_iface *ifa = n->ifa;
+  u8 cnt, missed;
+  u16 map=n->hello_map;
+
+  if (!map) return BABEL_INFINITY;
+  cnt = u32_popcount(map); // number of bits set
+  missed = n->hello_cnt-cnt;
+
+  if (ifa->cf->type == BABEL_IFACE_TYPE_WIRELESS)
+  {
+    /* ETX - Appendix 2.2 in the RFC.
+
+       beta = prob. of successful transmission.
+       rxcost = BABEL_RXCOST_WIRELESS/beta
+
+       Since: beta = 1-missed/n->hello_cnt = cnt/n->hello_cnt
+       Then: rxcost = BABEL_RXCOST_WIRELESS * n->hello_cnt / cnt
+   */
+    if (!cnt) return BABEL_INFINITY;
+    return BABEL_RXCOST_WIRELESS * n->hello_cnt / cnt;
+  }
+  else
+  {
+    /* k-out-of-j selection - Appendix 2.1 in the RFC. */
+    DBG("Babel: Missed %d hellos from %I\n", missed, n->addr);
+    /* Link is bad if more than half the expected hellos were lost */
+    return (missed > n->hello_cnt/2) ? BABEL_INFINITY : ifa->cf->rxcost;
+  }
+}
+
+
+static u16
+babel_compute_cost(struct babel_neighbor *n)
+{
+  struct babel_iface *ifa = n->ifa;
+  u16 rxcost = babel_compute_rxcost(n);
+  if (rxcost == BABEL_INFINITY) return rxcost;
+  else if (ifa->cf->type == BABEL_IFACE_TYPE_WIRELESS)
+  {
+    /* ETX - Appendix 2.2 in the RFC */
+    return (MAX(n->txcost, BABEL_RXCOST_WIRELESS) * rxcost)/BABEL_RXCOST_WIRELESS;
+  }
+  else
+  {
+    /* k-out-of-j selection - Appendix 2.1 in the RFC. */
+    return n->txcost;
+  }
+}
+
+/* Simple additive metric - Appendix 3.1 in the RFC */
+static u16
+babel_compute_metric(struct babel_neighbor *n, uint metric)
+{
+  metric += babel_compute_cost(n);
+  return MIN(metric, BABEL_INFINITY);
+}
+
+
+/**
+ * babel_announce_rte - announce selected route to the core
+ * @p: Babel protocol instance
+ * @e: Babel route entry to announce
+ *
+ * This function announces a Babel entry to the core if it has a selected
+ * incoming path, and retracts it otherwise. If the selected entry has infinite
+ * metric, the route is announced as unreachable.
+ */
+static void
+babel_announce_rte(struct babel_proto *p, struct babel_entry *e)
+{
+  struct babel_route *r = e->selected_in;
+
+  if (r)
+  {
+    net *n = net_get(p->p.table, e->n.prefix, e->n.pxlen);
+    rta A = {
+      .src = p->p.main_source,
+      .source = RTS_BABEL,
+      .scope = SCOPE_UNIVERSE,
+      .cast = RTC_UNICAST,
+      .dest = r->metric == BABEL_INFINITY ? RTD_UNREACHABLE : RTD_ROUTER,
+      .flags = 0,
+      .from = r->neigh->addr,
+      .iface = r->neigh->ifa->iface,
+    };
+
+    if (r->metric < BABEL_INFINITY)
+      A.gw = r->next_hop;
+
+    rta *a = rta_lookup(&A);
+    rte *rte = rte_get_temp(a);
+    rte->u.babel.metric = r->metric;
+    rte->u.babel.router_id = r->router_id;
+    rte->net = n;
+    rte->pflags = 0;
+
+    rte_update(&p->p, n, rte);
+  }
+  else
+  {
+    /* Retraction */
+    net *n = net_find(p->p.table, e->n.prefix, e->n.pxlen);
+    rte_update(&p->p, n, NULL);
+  }
+}
+
+/**
+ * babel_select_route - select best route for given route entry
+ * @e: Babel entry to select the best route for
+ *
+ * Select the best feasible route for a given prefix among the routes received
+ * from peers, and propagate it to the nest. This just selects the feasible
+ * route with the lowest metric.
+ *
+ * If no feasible route is available for a prefix that previously had a route
+ * selected, a seqno request is sent to try to get a valid route. In the
+ * meantime, the route is marked as infeasible in the nest (to blackhole packets
+ * going to it, as per the RFC).
+ *
+ * If no feasible route is available, and no previous route is selected, the
+ * route is removed from the nest entirely.
+ */
+static void
+babel_select_route(struct babel_entry *e)
+{
+  struct babel_proto *p = e->proto;
+  struct babel_route *r, *cur = e->selected_in;
+
+  /* try to find the best feasible route */
+  WALK_LIST(r, e->routes)
+    if (!OUR_ROUTE(r) && /* prevent propagating our own routes back to core */
+	(!cur || r->metric < cur->metric) &&
+        babel_is_feasible(babel_find_source(e, r->router_id), r->seqno, r->advert_metric))
+      cur = r;
+
+  if (cur && !OUR_ROUTE(cur) &&
+      ((!e->selected_in && cur->metric < BABEL_INFINITY) ||
+       (e->selected_in && cur->metric < e->selected_in->metric)))
+  {
+    TRACE(D_EVENTS, "Picked new route for prefix %I/%d: router id %lR metric %d",
+	  e->n.prefix, e->n.pxlen, cur->router_id, cur->metric);
+
+    e->selected_in = cur;
+    e->updated = now;
+    babel_announce_rte(p, e);
+  }
+  else if (!cur || cur->metric == BABEL_INFINITY)
+  {
+    /* Couldn't find a feasible route. If we have a selected route, that means
+       it just became infeasible; so set it's metric to infinite and install it
+       (as unreachable), then send a seqno request.
+
+       babel_build_rte() will set the unreachable flag if the metric is BABEL_INFINITY.*/
+    if (e->selected_in)
+    {
+      TRACE(D_EVENTS, "Lost feasible route for prefix %I/%d",
+	    e->n.prefix, e->n.pxlen);
+
+      e->selected_in->metric = BABEL_INFINITY;
+      e->updated = now;
+
+      babel_send_seqno_request(e);
+      babel_announce_rte(p, e);
+    }
+    else
+    {
+      /* No route currently selected, and no new one selected; this means we
+	 don't have a route to this destination anymore (and were probably
+	 called from an expiry timer). Remove the route from the nest. */
+      TRACE(D_EVENTS, "Flushing route for prefix %I/%d", e->n.prefix, e->n.pxlen);
+
+      e->selected_in = NULL;
+      e->updated = now;
+      babel_announce_rte(p, e);
+    }
+  }
+}
+
+/*
+ *	Functions to send replies
+ */
+
+static void
+babel_send_ack(struct babel_iface *ifa, ip_addr dest, u16 nonce)
+{
+  struct babel_proto *p = ifa->proto;
+  union babel_msg msg = {};
+
+  TRACE(D_PACKETS, "Sending ACK to %I with nonce %d", dest, nonce);
+
+  msg.type = BABEL_TLV_ACK;
+  msg.ack.nonce = nonce;
+
+  babel_send_unicast(&msg, ifa, dest);
+}
+
+static void
+babel_build_ihu(union babel_msg *msg, struct babel_iface *ifa, struct babel_neighbor *n)
+{
+  struct babel_proto *p = ifa->proto;
+
+  msg->type = BABEL_TLV_IHU;
+  msg->ihu.addr = n->addr;
+  msg->ihu.rxcost = babel_compute_rxcost(n);
+  msg->ihu.interval = ifa->cf->ihu_interval;
+
+  TRACE(D_PACKETS, "Sending IHU for %I with rxcost %d interval %d",
+        msg->ihu.addr, msg->ihu.rxcost, msg->ihu.interval);
+}
+
+static void
+babel_send_ihu(struct babel_iface *ifa, struct babel_neighbor *n)
+{
+  union babel_msg msg = {};
+  babel_build_ihu(&msg, ifa, n);
+  babel_send_unicast(&msg, ifa, n->addr);
+}
+
+static void
+babel_send_ihus(struct babel_iface *ifa)
+{
+  struct babel_neighbor *n;
+  WALK_LIST(n, ifa->neigh_list)
+  {
+    union babel_msg msg = {};
+    babel_build_ihu(&msg, ifa, n);
+    babel_enqueue(&msg, ifa);
+  }
+}
+
+static void
+babel_send_hello(struct babel_iface *ifa, u8 send_ihu)
+{
+  struct babel_proto *p = ifa->proto;
+  union babel_msg msg = {};
+
+  msg.type = BABEL_TLV_HELLO;
+  msg.hello.seqno = ifa->hello_seqno++;
+  msg.hello.interval = ifa->cf->hello_interval;
+
+  TRACE(D_PACKETS, "Sending hello on %s with seqno %d interval %d",
+	ifa->ifname, msg.hello.seqno, msg.hello.interval);
+
+  babel_enqueue(&msg, ifa);
+
+  if (send_ihu)
+    babel_send_ihus(ifa);
+}
+
+static void
+babel_send_route_request(struct babel_entry *e, struct babel_neighbor *n)
+{
+  struct babel_proto *p = e->proto;
+  struct babel_iface *ifa = n->ifa;
+  union babel_msg msg = {};
+
+  TRACE(D_PACKETS, "Sending route request for %I/%d to %I",
+        e->n.prefix, e->n.pxlen, n->addr);
+
+  msg.type = BABEL_TLV_ROUTE_REQUEST;
+  msg.route_request.prefix = e->n.prefix;
+  msg.route_request.plen = e->n.pxlen;
+
+  babel_send_unicast(&msg, ifa, n->addr);
+}
+
+static void
+babel_send_wildcard_request(struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+  union babel_msg msg = {};
+
+  TRACE(D_PACKETS, "Sending wildcard route request on %s",
+	ifa->ifname);
+
+  msg.type = BABEL_TLV_ROUTE_REQUEST;
+  msg.route_request.full = 1;
+
+  babel_enqueue(&msg, ifa);
+}
+
+static void
+babel_send_seqno_request(struct babel_entry *e)
+{
+  struct babel_proto *p = e->proto;
+  struct babel_route *r = e->selected_in;
+  struct babel_iface *ifa = NULL;
+  struct babel_source *s = NULL;
+  union babel_msg msg = {};
+
+  s = babel_find_source(e, r->router_id);
+  if (!s || !babel_cache_seqno_request(p, e->n.prefix, e->n.pxlen, r->router_id, s->seqno + 1))
+    return;
+
+  TRACE(D_PACKETS, "Sending seqno request for %I/%d router-id %lR seqno %d",
+	e->n.prefix, e->n.pxlen, r->router_id, s->seqno + 1);
+
+  msg.type = BABEL_TLV_SEQNO_REQUEST;
+  msg.seqno_request.plen = e->n.pxlen;
+  msg.seqno_request.seqno = s->seqno + 1;
+  msg.seqno_request.hop_count = BABEL_INITIAL_HOP_COUNT;
+  msg.seqno_request.router_id = r->router_id;
+  msg.seqno_request.prefix = e->n.prefix;
+
+  WALK_LIST(ifa, p->interfaces)
+    babel_enqueue(&msg, ifa);
+}
+
+static void
+babel_unicast_seqno_request(struct babel_route *r)
+{
+  struct babel_entry *e = r->e;
+  struct babel_proto *p = e->proto;
+  struct babel_iface *ifa = r->neigh->ifa;
+  struct babel_source *s = NULL;
+  union babel_msg msg = {};
+
+  s = babel_find_source(e, r->router_id);
+  if (!s || !babel_cache_seqno_request(p, e->n.prefix, e->n.pxlen, r->router_id, s->seqno + 1))
+    return;
+
+  TRACE(D_PACKETS, "Sending seqno request for %I/%d router-id %lR seqno %d",
+	e->n.prefix, e->n.pxlen, r->router_id, s->seqno + 1);
+
+  msg.type = BABEL_TLV_SEQNO_REQUEST;
+  msg.seqno_request.plen = e->n.pxlen;
+  msg.seqno_request.seqno = s->seqno + 1;
+  msg.seqno_request.hop_count = BABEL_INITIAL_HOP_COUNT;
+  msg.seqno_request.router_id = r->router_id;
+  msg.seqno_request.prefix = e->n.prefix;
+
+  babel_send_unicast(&msg, ifa, r->neigh->addr);
+}
+
+/**
+ * babel_send_update - send route table updates
+ * @ifa: Interface to transmit on
+ * @changed: Only send entries changed since this time
+ *
+ * This function produces update TLVs for all entries changed since the time
+ * indicated by the &changed parameter and queues them for transmission on the
+ * selected interface. During the process, the feasibility distance for each
+ * transmitted entry is updated.
+ */
+static void
+babel_send_update(struct babel_iface *ifa, bird_clock_t changed)
+{
+  struct babel_proto *p = ifa->proto;
+
+  FIB_WALK(&p->rtable, n)
+  {
+    struct babel_entry *e = (void *) n;
+    struct babel_route *r = e->selected_out;
+
+    if (!r)
+      continue;
+
+    /* Our own seqno might have changed, in which case we update the routes we
+       originate. */
+    if ((r->router_id == p->router_id) && (r->seqno < p->update_seqno))
+    {
+      r->seqno = p->update_seqno;
+      e->updated = now;
+    }
+
+    /* Skip routes that weren't updated since 'changed' time */
+    if (e->updated < changed)
+      continue;
+
+    TRACE(D_PACKETS, "Sending update for %I/%d router-id %lR seqno %d metric %d",
+	  e->n.prefix, e->n.pxlen, r->router_id, r->seqno, r->metric);
+
+    union babel_msg msg = {};
+    msg.type = BABEL_TLV_UPDATE;
+    msg.update.plen = e->n.pxlen;
+    msg.update.interval = ifa->cf->update_interval;
+    msg.update.seqno = r->seqno;
+    msg.update.metric = r->metric;
+    msg.update.prefix = e->n.prefix;
+    msg.update.router_id = r->router_id;
+
+    /* Update feasibility distance */
+    struct babel_source *s = babel_get_source(e, r->router_id);
+    s->expires = now + BABEL_GARBAGE_INTERVAL;
+    if ((msg.update.seqno > s->seqno) ||
+	((msg.update.seqno == s->seqno) && (msg.update.metric < s->metric)))
+    {
+      s->seqno = msg.update.seqno;
+      s->metric = msg.update.metric;
+    }
+    babel_enqueue(&msg, ifa);
+  }
+  FIB_WALK_END;
+}
+
+static void
+babel_trigger_iface_update(struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+
+  /* Interface not active or already scheduled */
+  if (!ifa->up || ifa->want_triggered)
+    return;
+
+  TRACE(D_EVENTS, "Scheduling triggered updates for %s seqno %d",
+	ifa->iface->name, p->update_seqno);
+
+  ifa->want_triggered = now;
+  babel_iface_kick_timer(ifa);
+}
+
+/* Sends and update on all interfaces. */
+static void
+babel_trigger_update(struct babel_proto *p)
+{
+  if (p->triggered)
+    return;
+
+  struct babel_iface *ifa;
+  WALK_LIST(ifa, p->interfaces)
+    babel_trigger_iface_update(ifa);
+
+  p->triggered = 1;
+}
+
+/* A retraction is an update with an infinite metric */
+static void
+babel_send_retraction(struct babel_iface *ifa, ip_addr prefix, int plen)
+{
+  struct babel_proto *p = ifa->proto;
+  union babel_msg msg = {};
+
+  TRACE(D_PACKETS, "Sending retraction for %I/%d router-id %lR seqno %d",
+	prefix, plen, p->router_id, p->update_seqno);
+
+  msg.type = BABEL_TLV_UPDATE;
+  msg.update.plen = plen;
+  msg.update.interval = ifa->cf->update_interval;
+  msg.update.seqno = p->update_seqno;
+  msg.update.metric = BABEL_INFINITY;
+  msg.update.prefix = prefix;
+  msg.update.router_id = p->router_id;
+
+  babel_enqueue(&msg, ifa);
+}
+
+
+/*
+ *	TLV handler helpers
+ */
+
+/* Update hello history according to Appendix A1 of the RFC */
+static void
+babel_update_hello_history(struct babel_neighbor *n, u16 seqno, u16 interval)
+{
+  /*
+   * Compute the difference between expected and received seqno (modulo 2^16).
+   * If the expected and received seqnos are within 16 of each other, the modular
+   * difference is going to be less than 16 for one of the directions. Otherwise,
+   * the values differ too much, so just reset the state.
+   */
+
+  u16 delta = ((uint) seqno - (uint) n->next_hello_seqno);
+
+  if (delta == 0)
+  {
+    /* Do nothing */
+  }
+  else if (delta <= 16)
+  {
+    /* Sending node decreased interval; fast-forward */
+    n->hello_map <<= delta;
+    n->hello_cnt = MIN(n->hello_cnt + delta, 16);
+  }
+  else if (delta >= 0xfff0)
+  {
+    u8 diff = (0xffff - delta);
+    /* Sending node increased interval; undo history */
+    n->hello_map >>= diff;
+    n->hello_cnt = (diff < n->hello_cnt) ? n->hello_cnt - diff : 0;
+  }
+  else
+  {
+    /* Note state reset - flush entries */
+    n->hello_map = n->hello_cnt = 0;
+  }
+
+  /* Current entry */
+  n->hello_map = (n->hello_map << 1) | 1;
+  n->next_hello_seqno = seqno+1;
+  if (n->hello_cnt < 16) n->hello_cnt++;
+  n->hello_expiry = now + BABEL_HELLO_EXPIRY_FACTOR(interval);
+}
+
+static void
+babel_expire_seqno_requests(struct babel_proto *p)
+{
+  struct babel_seqno_request *n, *nx;
+  WALK_LIST_DELSAFE(n, nx, p->seqno_cache)
+  {
+    if ((n->updated + BABEL_SEQNO_REQUEST_EXPIRY) <= now)
+    {
+      rem_node(NODE n);
+      sl_free(p->seqno_slab, n);
+    }
+  }
+}
+
+/*
+ * Checks the seqno request cache for a matching request and returns failure if
+ * found. Otherwise, a new entry is stored in the cache.
+ */
+static int
+babel_cache_seqno_request(struct babel_proto *p, ip_addr prefix, u8 plen,
+                          u64 router_id, u16 seqno)
+{
+  struct babel_seqno_request *r;
+
+  WALK_LIST(r, p->seqno_cache)
+  {
+    if (ipa_equal(r->prefix, prefix) && (r->plen == plen) &&
+	(r->router_id == router_id) && (r->seqno == seqno))
+      return 0;
+  }
+
+  /* no entries found */
+  r = sl_alloc(p->seqno_slab);
+  r->prefix = prefix;
+  r->plen = plen;
+  r->router_id = router_id;
+  r->seqno = seqno;
+  r->updated = now;
+  add_tail(&p->seqno_cache, NODE r);
+
+  return 1;
+}
+
+static void
+babel_forward_seqno_request(struct babel_entry *e,
+                            struct babel_msg_seqno_request *in,
+                            ip_addr sender)
+{
+  struct babel_proto *p = e->proto;
+  struct babel_route *r;
+
+  TRACE(D_PACKETS, "Forwarding seqno request for %I/%d router-id %lR seqno %d",
+	e->n.prefix, e->n.pxlen, in->router_id, in->seqno);
+
+  WALK_LIST(r, e->routes)
+  {
+    if ((r->router_id == in->router_id) &&
+	!OUR_ROUTE(r) &&
+	!ipa_equal(r->neigh->addr, sender))
+    {
+      if (!babel_cache_seqno_request(p, e->n.prefix, e->n.pxlen, in->router_id, in->seqno))
+	return;
+
+      union babel_msg msg = {};
+      msg.type = BABEL_TLV_SEQNO_REQUEST;
+      msg.seqno_request.plen = in->plen;
+      msg.seqno_request.seqno = in->seqno;
+      msg.seqno_request.hop_count = in->hop_count-1;
+      msg.seqno_request.router_id = in->router_id;
+      msg.seqno_request.prefix = e->n.prefix;
+
+      babel_send_unicast(&msg, r->neigh->ifa, r->neigh->addr);
+      return;
+    }
+  }
+}
+
+
+/*
+ *	TLV handlers
+ */
+
+void
+babel_handle_ack_req(union babel_msg *m, struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+  struct babel_msg_ack_req *msg = &m->ack_req;
+
+  TRACE(D_PACKETS, "Handling ACK request nonce %d interval %d",
+	msg->nonce, msg->interval);
+
+  babel_send_ack(ifa, msg->sender, msg->nonce);
+}
+
+void
+babel_handle_hello(union babel_msg *m, struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+  struct babel_msg_hello *msg = &m->hello;
+
+  TRACE(D_PACKETS, "Handling hello seqno %d interval %d",
+	msg->seqno, msg->interval);
+
+  struct babel_neighbor *n = babel_get_neighbor(ifa, msg->sender);
+  babel_update_hello_history(n, msg->seqno, msg->interval);
+  if (ifa->cf->type == BABEL_IFACE_TYPE_WIRELESS)
+    babel_send_ihu(ifa, n);
+}
+
+void
+babel_handle_ihu(union babel_msg *m, struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+  struct babel_msg_ihu *msg = &m->ihu;
+
+  /* Ignore IHUs that are not about us */
+  if ((msg->ae != BABEL_AE_WILDCARD) && !ipa_equal(msg->addr, ifa->addr))
+    return;
+
+  TRACE(D_PACKETS, "Handling IHU rxcost %d interval %d",
+	msg->rxcost, msg->interval);
+
+  struct babel_neighbor *n = babel_get_neighbor(ifa, msg->sender);
+  n->txcost = msg->rxcost;
+  n->ihu_expiry = now + BABEL_IHU_EXPIRY_FACTOR(msg->interval);
+}
+
+/**
+ * babel_handle_update - handle incoming route updates
+ * @m: Incoming update TLV
+ * @ifa: Interface the update was received on
+ *
+ * This function is called as a handler for update TLVs and handles the updating
+ * and maintenance of route entries in Babel's internal routing cache. The
+ * handling follows the actions described in the Babel RFC, and at the end of
+ * each update handling, babel_select_route() is called on the affected entry to
+ * optionally update the selected routes and propagate them to the core.
+ */
+void
+babel_handle_update(union babel_msg *m, struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+  struct babel_msg_update *msg = &m->update;
+
+  struct babel_neighbor *n;
+  struct babel_entry *e;
+  struct babel_source *s;
+  struct babel_route *r;
+  int feasible;
+
+  TRACE(D_PACKETS, "Handling update for %I/%d with seqno %d metric %d",
+	msg->prefix, msg->plen, msg->seqno, msg->metric);
+
+  n = babel_find_neighbor(ifa, msg->sender);
+  if (!n)
+  {
+    DBG("Babel: Haven't heard from neighbor %I; ignoring update.\n", msg->sender);
+    return;
+  }
+
+  if (msg->router_id == p->router_id)
+  {
+    DBG("Babel: Ignoring update for our own router ID.\n");
+    return;
+  }
+
+  /*
+   * RFC section 3.5.4:
+   *
+   * When a Babel node receives an update (id, prefix, seqno, metric) from a
+   * neighbour neigh with a link cost value equal to cost, it checks whether it
+   * already has a routing table entry indexed by (neigh, id, prefix).
+   *
+   * If no such entry exists:
+   *
+   * o if the update is unfeasible, it is ignored;
+   *
+   * o if the metric is infinite (the update is a retraction), the update is
+   *   ignored;
+   *
+   * o otherwise, a new route table entry is created, indexed by (neigh, id,
+   *   prefix), with seqno equal to seqno and an advertised metric equal to the
+   *   metric carried by the update.
+   *
+   * If such an entry exists:
+   *
+   * o if the entry is currently installed and the update is unfeasible, then
+   *   the behaviour depends on whether the router-ids of the two entries match.
+   *   If the router-ids are different, the update is treated as though it were
+   *   a retraction (i.e., as though the metric were FFFF hexadecimal). If the
+   *   router-ids are equal, the update is ignored;
+   *
+   * o otherwise (i.e., if either the update is feasible or the entry is not
+   *   currently installed), then the entry's sequence number, advertised
+   *   metric, metric, and router-id are updated and, unless the advertised
+   *   metric is infinite, the route's expiry timer is reset to a small multiple
+   *   of the Interval value included in the update.
+   */
+
+  if (msg->metric == BABEL_INFINITY)
+    e = babel_find_entry(p, msg->prefix, msg->plen);
+  else
+    e = babel_get_entry(p, msg->prefix, msg->plen);
+
+  if (!e)
+    return;
+
+  s = babel_find_source(e, msg->router_id); /* for feasibility */
+  r = babel_find_route(e, n); /* the route entry indexed by neighbour */
+  feasible = babel_is_feasible(s, msg->seqno, msg->metric);
+
+  if (!r)
+  {
+    if (!feasible || (msg->metric == BABEL_INFINITY))
+      return;
+
+    r = babel_get_route(e, n);
+    r->advert_metric = msg->metric;
+    r->router_id = msg->router_id;
+    r->metric = babel_compute_metric(n, msg->metric);
+    r->next_hop = msg->next_hop;
+    r->seqno = msg->seqno;
+  }
+  else if (r == r->e->selected_in && !feasible)
+  {
+    /* Route is installed and update is infeasible - we may lose the route, so
+       send a unicast seqno request (section 3.8.2.2 second paragraph). */
+    babel_unicast_seqno_request(r);
+
+    if (msg->router_id == r->router_id) return;
+    r->metric = BABEL_INFINITY; /* retraction */
+  }
+  else
+  {
+    /* Last paragraph above - update the entry */
+    r->advert_metric = msg->metric;
+    r->metric = babel_compute_metric(n, msg->metric);
+    r->router_id = msg->router_id;
+    r->next_hop = msg->next_hop;
+    r->seqno = msg->seqno;
+
+    if (msg->metric != BABEL_INFINITY)
+    {
+      r->expiry_interval = BABEL_ROUTE_EXPIRY_FACTOR(msg->interval);
+      r->expires = now + r->expiry_interval;
+      if (r->expiry_interval > BABEL_ROUTE_REFRESH_INTERVAL)
+        r->refresh_time = now + r->expiry_interval - BABEL_ROUTE_REFRESH_INTERVAL;
+    }
+
+    /* If the route is not feasible at this point, it means it is from another
+       neighbour than the one currently selected; so send a unicast seqno
+       request to try to get a better route (section 3.8.2.2 last paragraph). */
+    if (!feasible)
+      babel_unicast_seqno_request(r);
+  }
+
+  babel_select_route(e);
+}
+
+void
+babel_handle_route_request(union babel_msg *m, struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+  struct babel_msg_route_request *msg = &m->route_request;
+
+  /* RFC 6126 3.8.1.1 */
+
+  /* Wildcard request - full update on the interface */
+  if (msg->full)
+  {
+    TRACE(D_PACKETS, "Handling wildcard route request");
+    ifa->want_triggered = 1;
+    return;
+  }
+
+  TRACE(D_PACKETS, "Handling route request for %I/%d", msg->prefix, msg->plen);
+
+  /* Non-wildcard request - see if we have an entry for the route.
+     If not, send a retraction, otherwise send an update. */
+  struct babel_entry *e = babel_find_entry(p, msg->prefix, msg->plen);
+  if (!e)
+  {
+    babel_send_retraction(ifa, msg->prefix, msg->plen);
+  }
+  else
+  {
+    babel_trigger_iface_update(ifa);
+    e->updated = now;
+  }
+}
+
+
+void
+babel_handle_seqno_request(union babel_msg *m, struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+  struct babel_msg_seqno_request *msg = &m->seqno_request;
+
+  /* RFC 6126 3.8.1.2 */
+
+  TRACE(D_PACKETS, "Handling seqno request for %I/%d router-id %lR seqno %d hop count %d",
+	msg->prefix, msg->plen, msg->router_id, msg->seqno, msg->hop_count);
+
+  /* Ignore if we have no such entry or entry has infinite metric */
+  struct babel_entry *e = babel_find_entry(p, msg->prefix, msg->plen);
+  if (!e || !e->selected_out || (e->selected_out->metric == BABEL_INFINITY))
+    return;
+
+  /* Trigger update on incoming interface if we have a selected route with
+     different router id or seqno no smaller than requested */
+  struct babel_route *r = e->selected_out;
+  if ((r->router_id != msg->router_id) || ge_mod64k(r->seqno, msg->seqno))
+  {
+    babel_trigger_iface_update(ifa);
+    e->updated = now;
+    return;
+  }
+
+  /* Seqno is larger; check if we own the router id */
+  if (msg->router_id == p->router_id)
+  {
+    /* Ours; update seqno and trigger global update */
+    p->update_seqno++;
+    babel_trigger_update(p);
+  }
+  else
+  {
+    /* Not ours; forward if TTL allows it */
+    if (msg->hop_count > 1)
+      babel_forward_seqno_request(e, msg, msg->sender);
+  }
+}
+
+
+/*
+ *	Babel interfaces
+ */
+
+/**
+ * babel_iface_timer - Babel interface timer handler
+ * @t: Timer
+ *
+ * This function is called by the per-interface timer and triggers sending of
+ * periodic Hello's and both triggered and periodic updates. Periodic Hello's
+ * and updates are simply handled by setting the next_{hello,regular} variables
+ * on the interface, and triggering an update (and resetting the variable)
+ * whenever 'now' exceeds that value.
+ *
+ * For triggered updates, babel_trigger_iface_update() will set the
+ * want_triggered field on the interface to a timestamp value. If this is set
+ * (and the next_triggered time has passed; this is a rate limiting mechanism),
+ * babel_send_update() will be called with this timestamp as the second
+ * parameter. This causes updates to be send consisting of only the routes that
+ * have changed since the time saved in want_triggered.
+ *
+ * Mostly when an update is triggered, the route being modified will be set to
+ * the value of 'now' at the time of the trigger; the >= comparison for
+ * selecting which routes to send in the update will make sure this is included.
+ */
+static void
+babel_iface_timer(timer *t)
+{
+  struct babel_iface *ifa = t->data;
+  struct babel_proto *p = ifa->proto;
+  bird_clock_t hello_period = ifa->cf->hello_interval;
+  bird_clock_t update_period = ifa->cf->update_interval;
+
+  if (now >= ifa->next_hello)
+  {
+    babel_send_hello(ifa, (ifa->cf->type == BABEL_IFACE_TYPE_WIRELESS ||
+                           ifa->hello_seqno % BABEL_IHU_INTERVAL_FACTOR == 0));
+    ifa->next_hello +=  hello_period * (1 + (now - ifa->next_hello) / hello_period);
+  }
+
+  if (now >= ifa->next_regular)
+  {
+    TRACE(D_EVENTS, "Sending regular updates on %s", ifa->ifname);
+    babel_send_update(ifa, 0);
+    ifa->next_regular += update_period * (1 + (now - ifa->next_regular) / update_period);
+    ifa->want_triggered = 0;
+    p->triggered = 0;
+  }
+  else if (ifa->want_triggered && (now >= ifa->next_triggered))
+  {
+    TRACE(D_EVENTS, "Sending triggered updates on %s", ifa->ifname);
+    babel_send_update(ifa, ifa->want_triggered);
+    ifa->next_triggered = now + MIN(5, update_period / 2 + 1);
+    ifa->want_triggered = 0;
+    p->triggered = 0;
+  }
+
+  bird_clock_t next_event = MIN(ifa->next_hello, ifa->next_regular);
+  tm_start(ifa->timer, ifa->want_triggered ? 1 : (next_event - now));
+}
+
+static inline void
+babel_iface_kick_timer(struct babel_iface *ifa)
+{
+  if (ifa->timer->expires > (now + 1))
+    tm_start(ifa->timer, 1);
+}
+
+static void
+babel_iface_start(struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+
+  TRACE(D_EVENTS, "Starting interface %s", ifa->ifname);
+
+  ifa->next_hello = now + (random() % ifa->cf->hello_interval) + 1;
+  ifa->next_regular = now + (random() % ifa->cf->update_interval) + 1;
+  ifa->next_triggered = now + MIN(5, ifa->cf->update_interval / 2 + 1);
+  ifa->want_triggered = 0;	/* We send an immediate update (below) */
+  tm_start(ifa->timer, 1);
+  ifa->up = 1;
+
+  babel_send_hello(ifa, 0);
+  babel_send_wildcard_request(ifa);
+  babel_send_update(ifa, 0);	/* Full update */
+}
+
+static void
+babel_iface_stop(struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+  struct babel_neighbor *nbr;
+  struct babel_route *r;
+  node *n;
+
+  TRACE(D_EVENTS, "Stopping interface %s", ifa->ifname);
+
+  /*
+   * Rather than just flushing the neighbours, we set the metric of their routes
+   * to infinity. This allows us to keep the neighbour hello state for when the
+   * interface comes back up. The routes will also be kept until they expire.
+   */
+  WALK_LIST(nbr, ifa->neigh_list)
+  {
+    WALK_LIST(n, nbr->routes)
+    {
+      r = SKIP_BACK(struct babel_route, neigh_route, n);
+      r->metric = BABEL_INFINITY;
+      r->expires = now + r->expiry_interval;
+      babel_select_route(r->e);
+    }
+  }
+
+  tm_stop(ifa->timer);
+  ifa->up = 0;
+}
+
+static inline int
+babel_iface_link_up(struct babel_iface *ifa)
+{
+  return !ifa->cf->check_link || (ifa->iface->flags & IF_LINK_UP);
+}
+
+static void
+babel_iface_update_state(struct babel_iface *ifa)
+{
+  int up = ifa->sk && babel_iface_link_up(ifa);
+
+  if (up == ifa->up)
+    return;
+
+  if (up)
+    babel_iface_start(ifa);
+  else
+    babel_iface_stop(ifa);
+}
+
+static void
+babel_iface_update_buffers(struct babel_iface *ifa)
+{
+  if (!ifa->sk)
+    return;
+
+  uint mtu = MAX(BABEL_MIN_MTU, ifa->iface->mtu);
+  uint rbsize = ifa->cf->rx_buffer ?: mtu;
+  uint tbsize = ifa->cf->tx_length ?: mtu;
+  rbsize = MAX(rbsize, tbsize);
+
+  sk_set_rbsize(ifa->sk, rbsize);
+  sk_set_tbsize(ifa->sk, tbsize);
+
+  ifa->tx_length = tbsize - BABEL_OVERHEAD;
+}
+
+static struct babel_iface*
+babel_find_iface(struct babel_proto *p, struct iface *what)
+{
+  struct babel_iface *ifa;
+
+  WALK_LIST (ifa, p->interfaces)
+    if (ifa->iface == what)
+      return ifa;
+
+  return NULL;
+}
+
+static void
+babel_iface_locked(struct object_lock *lock)
+{
+  struct babel_iface *ifa = lock->data;
+  struct babel_proto *p = ifa->proto;
+
+  if (!babel_open_socket(ifa))
+  {
+    log(L_ERR "%s: Cannot open socket for %s", p->p.name, ifa->iface->name);
+    return;
+  }
+
+  babel_iface_update_buffers(ifa);
+  babel_iface_update_state(ifa);
+}
+
+static void
+babel_add_iface(struct babel_proto *p, struct iface *new, struct babel_iface_config *ic)
+{
+  struct babel_iface *ifa;
+
+  TRACE(D_EVENTS, "Adding interface %s", new->name);
+
+  pool *pool = rp_new(p->p.pool, new->name);
+
+  ifa = mb_allocz(pool, sizeof(struct babel_iface));
+  ifa->proto = p;
+  ifa->iface = new;
+  ifa->cf = ic;
+  ifa->pool = pool;
+  ifa->ifname = new->name;
+
+  add_tail(&p->interfaces, NODE ifa);
+
+  struct ifa *addr;
+  WALK_LIST(addr, new->addrs)
+    if (ipa_is_link_local(addr->ip))
+      ifa->addr = addr->ip;
+
+  if (ipa_zero(ifa->addr))
+    log(L_WARN "%s: Cannot find link-local addr on %s", p->p.name, new->name);
+
+  init_list(&ifa->neigh_list);
+  ifa->hello_seqno = 1;
+
+  ifa->timer = tm_new_set(ifa->pool, babel_iface_timer, ifa, 0, 0);
+
+  init_list(&ifa->msg_queue);
+  ifa->send_event = ev_new(ifa->pool);
+  ifa->send_event->hook = babel_send_queue;
+  ifa->send_event->data = ifa;
+
+  struct object_lock *lock = olock_new(ifa->pool);
+  lock->type = OBJLOCK_UDP;
+  lock->addr = IP6_BABEL_ROUTERS;
+  lock->port = ifa->cf->port;
+  lock->iface = ifa->iface;
+  lock->hook = babel_iface_locked;
+  lock->data = ifa;
+
+  olock_acquire(lock);
+}
+
+static void
+babel_remove_iface(struct babel_proto *p, struct babel_iface *ifa)
+{
+  TRACE(D_EVENTS, "Removing interface %s", ifa->iface->name);
+
+  struct babel_neighbor *n;
+  WALK_LIST_FIRST(n, ifa->neigh_list)
+    babel_flush_neighbor(n);
+
+  rem_node(NODE ifa);
+
+  rfree(ifa->pool); /* contains ifa itself, locks, socket, etc */
+}
+
+static void
+babel_if_notify(struct proto *P, unsigned flags, struct iface *iface)
+{
+  struct babel_proto *p = (void *) P;
+  struct babel_config *cf = (void *) P->cf;
+
+  if (iface->flags & IF_IGNORE)
+    return;
+
+  if (flags & IF_CHANGE_UP)
+  {
+    struct babel_iface_config *ic = (void *) iface_patt_find(&cf->iface_list, iface, iface->addr);
+
+    /* we only speak multicast */
+    if (!(iface->flags & IF_MULTICAST))
+      return;
+
+    if (ic)
+      babel_add_iface(p, iface, ic);
+
+    return;
+  }
+
+  struct babel_iface *ifa = babel_find_iface(p, iface);
+
+  if (!ifa)
+    return;
+
+  if (flags & IF_CHANGE_DOWN)
+  {
+    babel_remove_iface(p, ifa);
+    return;
+  }
+
+  if (flags & IF_CHANGE_MTU)
+    babel_iface_update_buffers(ifa);
+
+  if (flags & IF_CHANGE_LINK)
+    babel_iface_update_state(ifa);
+}
+
+static int
+babel_reconfigure_iface(struct babel_proto *p, struct babel_iface *ifa, struct babel_iface_config *new)
+{
+  struct babel_iface_config *old = ifa->cf;
+
+  /* Change of these options would require to reset the iface socket */
+  if ((new->port != old->port) ||
+      (new->tx_tos != old->tx_tos) ||
+      (new->tx_priority != old->tx_priority))
+    return 0;
+
+  TRACE(D_EVENTS, "Reconfiguring interface %s", ifa->iface->name);
+
+  ifa->cf = new;
+
+  if (ifa->next_regular > (now + new->update_interval))
+    ifa->next_regular = now + (random() % new->update_interval) + 1;
+
+  if ((new->tx_length != old->tx_length) || (new->rx_buffer != old->rx_buffer))
+    babel_iface_update_buffers(ifa);
+
+  if (new->check_link != old->check_link)
+    babel_iface_update_state(ifa);
+
+  if (ifa->up)
+    babel_iface_kick_timer(ifa);
+
+  return 1;
+}
+
+static void
+babel_reconfigure_ifaces(struct babel_proto *p, struct babel_config *cf)
+{
+  struct iface *iface;
+
+  WALK_LIST(iface, iface_list)
+  {
+    if (! (iface->flags & IF_UP))
+      continue;
+
+    struct babel_iface *ifa = babel_find_iface(p, iface);
+    struct babel_iface_config *ic = (void *) iface_patt_find(&cf->iface_list, iface, NULL);
+
+    if (ifa && ic)
+    {
+      if (babel_reconfigure_iface(p, ifa, ic))
+	continue;
+
+      /* Hard restart */
+      log(L_INFO "%s: Restarting interface %s", p->p.name, ifa->iface->name);
+      babel_remove_iface(p, ifa);
+      babel_add_iface(p, iface, ic);
+    }
+
+    if (ifa && !ic)
+      babel_remove_iface(p, ifa);
+
+    if (!ifa && ic)
+      babel_add_iface(p, iface, ic);
+  }
+}
+
+
+/*
+ *	Debugging and info output functions
+ */
+
+static void
+babel_dump_source(struct babel_source *s)
+{
+  debug("Source router_id %lR seqno %d metric %d expires %d\n",
+	s->router_id, s->seqno, s->metric, s->expires ? s->expires-now : 0);
+}
+
+static void
+babel_dump_route(struct babel_route *r)
+{
+  debug("Route neigh %I if %s seqno %d metric %d/%d router_id %lR expires %d\n",
+	r->neigh ? r->neigh->addr : IPA_NONE,
+        r->neigh ? r->neigh->ifa->ifname : "(none)",
+        r->seqno, r->advert_metric, r->metric,
+	r->router_id, r->expires ? r->expires-now : 0);
+}
+
+static void
+babel_dump_entry(struct babel_entry *e)
+{
+  struct babel_source *s;
+  struct babel_route *r;
+
+  debug("Babel: Entry %I/%d:\n", e->n.prefix, e->n.pxlen);
+
+  WALK_LIST(s,e->sources)
+  { debug(" "); babel_dump_source(s); }
+
+  WALK_LIST(r,e->routes)
+  {
+    debug(" ");
+    if (r == e->selected_out) debug("*");
+    if (r == e->selected_in) debug("+");
+    babel_dump_route(r);
+  }
+}
+
+static void
+babel_dump_neighbor(struct babel_neighbor *n)
+{
+  debug("Neighbor %I txcost %d hello_map %x next seqno %d expires %d/%d\n",
+	n->addr, n->txcost, n->hello_map, n->next_hello_seqno,
+        n->hello_expiry ? n->hello_expiry - now : 0,
+        n->ihu_expiry ? n->ihu_expiry - now : 0);
+}
+
+static void
+babel_dump_iface(struct babel_iface *ifa)
+{
+  struct babel_neighbor *n;
+
+  debug("Babel: Interface %s addr %I rxcost %d type %d hello seqno %d intervals %d %d\n",
+	ifa->ifname, ifa->addr, ifa->cf->rxcost, ifa->cf->type, ifa->hello_seqno,
+	ifa->cf->hello_interval, ifa->cf->update_interval);
+
+  WALK_LIST(n, ifa->neigh_list)
+  { debug(" "); babel_dump_neighbor(n); }
+}
+
+static void
+babel_dump(struct proto *P)
+{
+  struct babel_proto *p = (struct babel_proto *) P;
+  struct babel_iface *ifa;
+
+  debug("Babel: router id %lR update seqno %d\n", p->router_id, p->update_seqno);
+
+  WALK_LIST(ifa, p->interfaces)
+    babel_dump_iface(ifa);
+
+  FIB_WALK(&p->rtable, n)
+  {
+    babel_dump_entry((struct babel_entry *) n);
+  }
+  FIB_WALK_END;
+}
+
+static void
+babel_get_route_info(rte *rte, byte *buf, ea_list *attrs)
+{
+  buf += bsprintf(buf, " (%d/%d) [%lR]", rte->pref, rte->u.babel.metric, rte->u.babel.router_id);
+}
+
+static int
+babel_get_attr(eattr *a, byte *buf, int buflen UNUSED)
+{
+  switch (a->id)
+  {
+  case EA_BABEL_METRIC:
+    bsprintf(buf, "metric: %d", a->u.data);
+    return GA_FULL;
+
+  case EA_BABEL_ROUTER_ID:
+  {
+    u64 rid = 0;
+    memcpy(&rid, a->u.ptr->data, sizeof(u64));
+    bsprintf(buf, "router_id: %lR", rid);
+    return GA_FULL;
+  }
+
+  default:
+    return GA_UNKNOWN;
+  }
+}
+
+void
+babel_show_interfaces(struct proto *P, char *iff)
+{
+  struct babel_proto *p = (void *) P;
+  struct babel_iface *ifa = NULL;
+  struct babel_neighbor *nbr = NULL;
+
+  if (p->p.proto_state != PS_UP)
+  {
+    cli_msg(-1023, "%s: is not up", p->p.name);
+    cli_msg(0, "");
+    return;
+  }
+
+  cli_msg(-1023, "%s:", p->p.name);
+  cli_msg(-1023, "%-10s %-6s %7s %6s %6s",
+	  "Interface", "State", "RX cost", "Nbrs", "Timer");
+
+  WALK_LIST(ifa, p->interfaces)
+  {
+    if (iff && !patmatch(iff, ifa->iface->name))
+      continue;
+
+    int nbrs = 0;
+    WALK_LIST(nbr, ifa->neigh_list)
+	nbrs++;
+
+    int timer = MIN(ifa->next_regular, ifa->next_hello) - now;
+    cli_msg(-1023, "%-10s %-6s %7u %6u %6u",
+	    ifa->iface->name, (ifa->up ? "Up" : "Down"), ifa->cf->rxcost, nbrs, MAX(timer, 0));
+  }
+
+  cli_msg(0, "");
+}
+
+void
+babel_show_neighbors(struct proto *P, char *iff)
+{
+  struct babel_proto *p = (void *) P;
+  struct babel_iface *ifa = NULL;
+  struct babel_neighbor *n = NULL;
+  struct babel_route *r = NULL;
+
+  if (p->p.proto_state != PS_UP)
+  {
+    cli_msg(-1024, "%s: is not up", p->p.name);
+    cli_msg(0, "");
+    return;
+  }
+
+  cli_msg(-1024, "%s:", p->p.name);
+  cli_msg(-1024, "%-25s %-10s %6s %6s %10s",
+	  "IP address", "Interface", "Metric", "Routes", "Next hello");
+
+  WALK_LIST(ifa, p->interfaces)
+  {
+    if (iff && !patmatch(iff, ifa->iface->name))
+      continue;
+
+    WALK_LIST(n, ifa->neigh_list)
+    {
+      int rts = 0;
+      WALK_LIST(r, n->routes)
+        rts++;
+
+      int timer = n->hello_expiry - now;
+      cli_msg(-1024, "%-25I %-10s %6u %6u %10u",
+	      n->addr, ifa->iface->name, n->txcost, rts, MAX(timer, 0));
+    }
+  }
+
+  cli_msg(0, "");
+}
+
+void
+babel_show_entries(struct proto *P)
+{
+  struct babel_proto *p = (void *) P;
+  struct babel_entry *e = NULL;
+  struct babel_source *s = NULL;
+  struct babel_route *r = NULL;
+
+  char ipbuf[STD_ADDRESS_P_LENGTH+5];
+  char ridbuf[ROUTER_ID_64_LENGTH+1];
+
+  if (p->p.proto_state != PS_UP)
+  {
+    cli_msg(-1025, "%s: is not up", p->p.name);
+    cli_msg(0, "");
+    return;
+  }
+
+  cli_msg(-1025, "%s:", p->p.name);
+  cli_msg(-1025, "%-29s %-23s %6s %5s %7s %7s",
+	  "Prefix", "Router ID", "Metric", "Seqno", "Expires", "Sources");
+
+  FIB_WALK(&p->rtable, n)
+  {
+    e = (struct babel_entry *) n;
+    r = e->selected_in ? e->selected_in : e->selected_out;
+
+    int srcs = 0;
+    WALK_LIST(s, e->sources)
+      srcs++;
+
+    bsprintf(ipbuf, "%I/%u", e->n.prefix, e->n.pxlen);
+
+    if (r)
+    {
+      if (r->router_id == p->router_id)
+        bsprintf(ridbuf, "%s", "<self>");
+      else
+        bsprintf(ridbuf, "%lR", r->router_id);
+
+      int time = r->expires ? r->expires - now : 0;
+      cli_msg(-1025, "%-29s %-23s %6u %5u %7u %7u",
+	      ipbuf, ridbuf, r->metric, r->seqno, MAX(time, 0), srcs);
+    }
+    else
+    {
+      cli_msg(-1025, "%-29s %-44s %7u", ipbuf, "<pending>", srcs);
+    }
+  }
+  FIB_WALK_END;
+
+  cli_msg(0, "");
+}
+
+
+/*
+ *	Babel protocol glue
+ */
+
+/**
+ * babel_timer - global timer hook
+ * @t: Timer
+ *
+ * This function is called by the global protocol instance timer and handles
+ * expiration of routes and neighbours as well as pruning of the seqno request
+ * cache.
+ */
+static void
+babel_timer(timer *t)
+{
+  struct babel_proto *p = t->data;
+
+  babel_expire_routes(p);
+  babel_expire_seqno_requests(p);
+  babel_expire_neighbors(p);
+}
+
+static inline void
+babel_kick_timer(struct babel_proto *p)
+{
+  if (p->timer->expires > (now + 1))
+    tm_start(p->timer, 1);
+}
+
+
+static struct ea_list *
+babel_prepare_attrs(struct linpool *pool, ea_list *next, uint metric, u64 router_id)
+{
+  struct ea_list *l = lp_alloc(pool, sizeof(struct ea_list) + 2*sizeof(eattr));
+  struct adata *rid = lp_alloc(pool, sizeof(struct adata) + sizeof(u64));
+  rid->length = sizeof(u64);
+  memcpy(&rid->data, &router_id, sizeof(u64));
+
+  l->next = next;
+  l->flags = EALF_SORTED;
+  l->count = 2;
+
+  l->attrs[0].id = EA_BABEL_METRIC;
+  l->attrs[0].flags = 0;
+  l->attrs[0].type = EAF_TYPE_INT | EAF_TEMP;
+  l->attrs[0].u.data = metric;
+
+  l->attrs[1].id = EA_BABEL_ROUTER_ID;
+  l->attrs[1].flags = 0;
+  l->attrs[1].type = EAF_TYPE_OPAQUE | EAF_TEMP;
+  l->attrs[1].u.ptr = rid;
+
+  return l;
+}
+
+
+static int
+babel_import_control(struct proto *P, struct rte **rt, struct ea_list **attrs, struct linpool *pool)
+{
+  struct babel_proto *p = (void *) P;
+
+  /* Prepare attributes with initial values */
+  if ((*rt)->attrs->source != RTS_BABEL)
+    *attrs = babel_prepare_attrs(pool, NULL, 0, p->router_id);
+
+  return 0;
+}
+
+static struct ea_list *
+babel_make_tmp_attrs(struct rte *rt, struct linpool *pool)
+{
+  return babel_prepare_attrs(pool, NULL, rt->u.babel.metric, rt->u.babel.router_id);
+}
+
+static void
+babel_store_tmp_attrs(struct rte *rt, struct ea_list *attrs)
+{
+  rt->u.babel.metric = ea_get_int(attrs, EA_BABEL_METRIC, 0);
+}
+
+/*
+ * babel_rt_notify - core tells us about new route (possibly our own),
+ * so store it into our data structures.
+ */
+static void
+babel_rt_notify(struct proto *P, struct rtable *table UNUSED, struct network *net,
+		struct rte *new, struct rte *old, struct ea_list *attrs)
+{
+  struct babel_proto *p = (void *) P;
+  struct babel_entry *e;
+  struct babel_route *r;
+
+  if (new)
+  {
+    /* Update */
+    e = babel_get_entry(p, net->n.prefix, net->n.pxlen);
+
+    if (new->attrs->src->proto != P)
+    {
+      r = babel_get_route(e, NULL);
+      r->seqno = p->update_seqno;
+      r->router_id = p->router_id;
+      r->metric = 0;	/* FIXME: should be selectable */
+    }
+    else
+      r = e->selected_in;
+
+    if (r != e->selected_out)
+    {
+      e->selected_out = r;
+      e->updated = now;
+      babel_trigger_update(p);
+    }
+  }
+  else
+  {
+    /* Withdraw */
+    e = babel_find_entry(p, net->n.prefix, net->n.pxlen);
+    if (!e || !e->selected_out)
+      return;
+
+    if (OUR_ROUTE(e->selected_out))
+    {
+      /*
+       * We originate this route, so set its metric to infinity and set an
+       * expiry time. This causes a retraction to be sent, and later the route
+       * to be flushed once the hold time has passed.
+       */
+      e->selected_out->metric = BABEL_INFINITY;
+      e->selected_out->expires = now + BABEL_HOLD_TIME;
+      e->updated = now;
+      babel_trigger_update(p);
+    }
+    else
+    {
+      /*
+       * This is a route originating from someone else that was lost; presumably
+       * because an export filter was updated to filter it. This means we can't
+       * set the metric to infinity (it would be overridden on subsequent
+       * updates from the peer originating the route), so just clear the
+       * exported route.
+       *
+       * This causes peers to expire the route after a while (like if we just
+       * shut down), but it's the best we can do in these circumstances; and
+       * since export filters presumably aren't updated that often this is
+       * acceptable.
+       */
+      e->selected_out = NULL;
+    }
+  }
+}
+
+static int
+babel_rte_better(struct rte *new, struct rte *old)
+{
+  return new->u.babel.metric < old->u.babel.metric;
+}
+
+static int
+babel_rte_same(struct rte *new, struct rte *old)
+{
+  return ((new->u.babel.router_id == old->u.babel.router_id) &&
+          (new->u.babel.metric == old->u.babel.metric));
+}
+
+
+static struct proto *
+babel_init(struct proto_config *cfg)
+{
+  struct proto *P = proto_new(cfg, sizeof(struct babel_proto));
+
+  P->accept_ra_types = RA_OPTIMAL;
+  P->if_notify = babel_if_notify;
+  P->rt_notify = babel_rt_notify;
+  P->import_control = babel_import_control;
+  P->make_tmp_attrs = babel_make_tmp_attrs;
+  P->store_tmp_attrs = babel_store_tmp_attrs;
+  P->rte_better = babel_rte_better;
+  P->rte_same = babel_rte_same;
+
+  return P;
+}
+
+static int
+babel_start(struct proto *P)
+{
+  struct babel_proto *p = (void *) P;
+  struct babel_config *cf = (void *) P->cf;
+
+  fib_init(&p->rtable, P->pool, sizeof(struct babel_entry), 0, babel_init_entry);
+  init_list(&p->interfaces);
+  p->timer = tm_new_set(P->pool, babel_timer, p, 0, 1);
+  tm_start(p->timer, 2);
+  p->update_seqno = 1;
+  p->router_id = proto_get_router_id(&cf->c);
+
+  p->route_slab = sl_new(P->pool, sizeof(struct babel_route));
+  p->source_slab = sl_new(P->pool, sizeof(struct babel_source));
+  p->msg_slab = sl_new(P->pool, sizeof(struct babel_msg_node));
+  p->seqno_slab = sl_new(P->pool, sizeof(struct babel_seqno_request));
+  init_list(&p->seqno_cache);
+
+  p->log_pkt_tbf = (struct tbf){ .rate = 1, .burst = 5 };
+
+  return PS_UP;
+}
+
+static int
+babel_reconfigure(struct proto *P, struct proto_config *c)
+{
+  struct babel_proto *p = (void *) P;
+  struct babel_config *new = (void *) c;
+
+  TRACE(D_EVENTS, "Reconfiguring");
+
+  p->p.cf = c;
+  babel_reconfigure_ifaces(p, new);
+
+  babel_trigger_update(p);
+  babel_kick_timer(p);
+
+  return 1;
+}
+
+
+struct protocol proto_babel = {
+  .name =		"Babel",
+  .template =		"babel%d",
+  .attr_class =		EAP_BABEL,
+  .preference =		DEF_PREF_BABEL,
+  .config_size =	sizeof(struct babel_config),
+  .init =		babel_init,
+  .dump =		babel_dump,
+  .start =		babel_start,
+  .reconfigure =	babel_reconfigure,
+  .get_route_info =	babel_get_route_info,
+  .get_attr =		babel_get_attr
+};
diff --git a/proto/babel/babel.h b/proto/babel/babel.h
new file mode 100644
index 00000000..aea0dd88
--- /dev/null
+++ b/proto/babel/babel.h
@@ -0,0 +1,335 @@
+/*
+ *	BIRD -- The Babel protocol
+ *
+ *	Copyright (c) 2015--2016 Toke Hoiland-Jorgensen
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ *
+ *	This file contains the data structures used by Babel.
+ */
+
+#ifndef _BIRD_BABEL_H_
+#define _BIRD_BABEL_H_
+
+#include "nest/bird.h"
+#include "nest/cli.h"
+#include "nest/iface.h"
+#include "nest/route.h"
+#include "nest/protocol.h"
+#include "nest/locks.h"
+#include "lib/resource.h"
+#include "lib/lists.h"
+#include "lib/socket.h"
+#include "lib/string.h"
+#include "lib/timer.h"
+
+#ifndef IPV6
+#error "The Babel protocol only speaks IPv6"
+#endif
+
+#define EA_BABEL_METRIC		EA_CODE(EAP_BABEL, 0)
+#define EA_BABEL_ROUTER_ID	EA_CODE(EAP_BABEL, 1)
+
+#define BABEL_MAGIC		42
+#define BABEL_VERSION		2
+#define BABEL_PORT		6696
+#define BABEL_INFINITY		0xFFFF
+
+
+#define BABEL_HELLO_INTERVAL_WIRED	4	/* Default hello intervals in seconds */
+#define BABEL_HELLO_INTERVAL_WIRELESS	4
+#define BABEL_UPDATE_INTERVAL_FACTOR	4
+#define BABEL_IHU_INTERVAL_FACTOR	3
+#define BABEL_IHU_EXPIRY_FACTOR(X)	((X)*3/2)	/* 1.5 */
+#define BABEL_HELLO_EXPIRY_FACTOR(X)	((X)*3/2)	/* 1.5 */
+#define BABEL_ROUTE_EXPIRY_FACTOR(X)	((X)*7/2)	/* 3.5 */
+#define BABEL_ROUTE_REFRESH_INTERVAL	2	/* Seconds before route expiry to send route request */
+#define BABEL_HOLD_TIME			10	/* Expiry time for our own routes */
+#define BABEL_RXCOST_WIRED		96
+#define BABEL_RXCOST_WIRELESS		256
+#define BABEL_INITIAL_HOP_COUNT		255
+#define BABEL_MAX_SEND_INTERVAL		5
+#define BABEL_TIME_UNITS		100	/* On-wire times are counted in centiseconds */
+
+#define BABEL_SEQNO_REQUEST_EXPIRY	60
+#define BABEL_GARBAGE_INTERVAL		300
+
+#define BABEL_OVERHEAD		(SIZE_OF_IP_HEADER+UDP_HEADER_LENGTH)
+#define BABEL_MIN_MTU		(512 + BABEL_OVERHEAD)
+
+
+enum babel_tlv_type {
+  BABEL_TLV_PAD1		= 0,
+  BABEL_TLV_PADN		= 1,
+  BABEL_TLV_ACK_REQ		= 2,
+  BABEL_TLV_ACK			= 3,
+  BABEL_TLV_HELLO		= 4,
+  BABEL_TLV_IHU 		= 5,
+  BABEL_TLV_ROUTER_ID		= 6,
+  BABEL_TLV_NEXT_HOP		= 7,
+  BABEL_TLV_UPDATE		= 8,
+  BABEL_TLV_ROUTE_REQUEST	= 9,
+  BABEL_TLV_SEQNO_REQUEST	= 10,
+  /* extensions - not implemented
+  BABEL_TLV_TS_PC		= 11,
+  BABEL_TLV_HMAC		= 12,
+  BABEL_TLV_SS_UPDATE		= 13,
+  BABEL_TLV_SS_REQUEST		= 14,
+  BABEL_TLV_SS_SEQNO_REQUEST	= 15,
+  */
+  BABEL_TLV_MAX
+};
+
+enum babel_iface_type {
+  /* In practice, UNDEF and WIRED give equivalent behaviour */
+  BABEL_IFACE_TYPE_UNDEF	= 0,
+  BABEL_IFACE_TYPE_WIRED	= 1,
+  BABEL_IFACE_TYPE_WIRELESS	= 2,
+  BABEL_IFACE_TYPE_MAX
+};
+
+enum babel_ae_type {
+  BABEL_AE_WILDCARD		= 0,
+  BABEL_AE_IP4			= 1,
+  BABEL_AE_IP6			= 2,
+  BABEL_AE_IP6_LL		= 3,
+  BABEL_AE_MAX
+};
+
+
+struct babel_config {
+  struct proto_config c;
+
+  list iface_list;              /* Patterns configured -- keep it first; see babel_reconfigure why */
+};
+
+struct babel_iface_config {
+  struct iface_patt i;
+
+  u16 rxcost;
+  u8 type;
+  u8 check_link;
+  int port;
+  u16 hello_interval;
+  u16 ihu_interval;
+  u16 update_interval;
+
+  u16 rx_buffer;			/* RX buffer size, 0 for MTU */
+  u16 tx_length;			/* TX packet length limit (including headers), 0 for MTU */
+  int tx_tos;
+  int tx_priority;
+};
+
+struct babel_proto {
+  struct proto p;
+  timer *timer;
+  struct fib rtable;
+  list interfaces;			/* Interfaces we really know about (struct babel_iface) */
+  u64 router_id;
+  u16 update_seqno;			/* To be increased on request */
+  u8 triggered;				/* For triggering global updates */
+
+  slab *route_slab;
+  slab *source_slab;
+  slab *msg_slab;
+
+  slab *seqno_slab;
+  list seqno_cache;			/* Seqno requests in the cache (struct babel_seqno_request) */
+
+  struct tbf log_pkt_tbf;		/* TBF for packet messages */
+};
+
+struct babel_iface {
+  node n;
+
+  struct babel_proto *proto;
+  struct iface *iface;
+
+  struct babel_iface_config *cf;
+
+  u8 up;
+
+  pool *pool;
+  char *ifname;
+  sock *sk;
+  ip_addr addr;
+  int tx_length;
+  list neigh_list;			/* List of neighbors seen on this iface (struct babel_neighbor) */
+  list msg_queue;
+
+  u16 hello_seqno;			/* To be increased on each hello */
+
+  bird_clock_t next_hello;
+  bird_clock_t next_regular;
+  bird_clock_t next_triggered;
+  bird_clock_t want_triggered;
+
+  timer *timer;
+  event *send_event;
+};
+
+struct babel_neighbor {
+  node n;
+  struct babel_iface *ifa;
+
+  ip_addr addr;
+  u16 txcost;
+  u8 hello_cnt;
+  u16 hello_map;
+  u16 next_hello_seqno;
+  /* expiry timers */
+  bird_clock_t hello_expiry;
+  bird_clock_t ihu_expiry;
+
+  list routes;				/* Routes this neighbour has sent us (struct babel_route) */
+};
+
+struct babel_source {
+  node n;
+
+  u64 router_id;
+  u16 seqno;
+  u16 metric;
+  bird_clock_t expires;
+};
+
+struct babel_route {
+  node n;
+  node neigh_route;
+  struct babel_entry    *e;
+  struct babel_neighbor *neigh;
+
+  u16 seqno;
+  u16 advert_metric;
+  u16 metric;
+  u64 router_id;
+  ip_addr next_hop;
+  bird_clock_t refresh_time;
+  bird_clock_t expires;
+  u16 expiry_interval;
+};
+
+struct babel_entry {
+  struct fib_node n;
+  struct babel_proto *proto;
+  struct babel_route *selected_in;
+  struct babel_route *selected_out;
+
+  bird_clock_t updated;
+
+  list sources;				/* Source entries for this prefix (struct babel_source). */
+  list routes;				/* Routes for this prefix (struct babel_route) */
+};
+
+/* Stores forwarded seqno requests for duplicate suppression. */
+struct babel_seqno_request {
+  node n;
+  ip_addr prefix;
+  u8  plen;
+  u64 router_id;
+  u16 seqno;
+  bird_clock_t updated;
+};
+
+
+/*
+ *	Internal TLV messages
+ */
+
+struct babel_msg_ack_req {
+  u8 type;
+  u16 nonce;
+  u16 interval;
+  ip_addr sender;
+};
+
+struct babel_msg_ack {
+  u8 type;
+  u16 nonce;
+};
+
+struct babel_msg_hello {
+  u8 type;
+  u16 seqno;
+  u16 interval;
+  ip_addr sender;
+};
+
+struct babel_msg_ihu {
+  u8 type;
+  u8 ae;
+  u16 rxcost;
+  u16 interval;
+  ip_addr addr;
+  ip_addr sender;
+};
+
+struct babel_msg_update {
+  u8 type;
+  u8 ae;
+  u8 plen;
+  u16 interval;
+  u16 seqno;
+  u16 metric;
+  ip_addr prefix;
+  u64 router_id;
+  ip_addr next_hop;
+  ip_addr sender;
+};
+
+struct babel_msg_route_request {
+  u8 type;
+  u8 full;
+  u8 plen;
+  ip_addr prefix;
+};
+
+struct babel_msg_seqno_request {
+  u8 type;
+  u8 plen;
+  u16 seqno;
+  u8 hop_count;
+  u64 router_id;
+  ip_addr prefix;
+  ip_addr sender;
+};
+
+union babel_msg {
+  u8 type;
+  struct babel_msg_ack_req ack_req;
+  struct babel_msg_ack ack;
+  struct babel_msg_hello hello;
+  struct babel_msg_ihu ihu;
+  struct babel_msg_update update;
+  struct babel_msg_route_request route_request;
+  struct babel_msg_seqno_request seqno_request;
+};
+
+struct babel_msg_node {
+  node n;
+  union babel_msg msg;
+};
+
+
+/* babel.c */
+void babel_handle_ack_req(union babel_msg *msg, struct babel_iface *ifa);
+void babel_handle_ack(union babel_msg *msg, struct babel_iface *ifa);
+void babel_handle_hello(union babel_msg *msg, struct babel_iface *ifa);
+void babel_handle_ihu(union babel_msg *msg, struct babel_iface *ifa);
+void babel_handle_router_id(union babel_msg *msg, struct babel_iface *ifa);
+void babel_handle_update(union babel_msg *msg, struct babel_iface *ifa);
+void babel_handle_route_request(union babel_msg *msg, struct babel_iface *ifa);
+void babel_handle_seqno_request(union babel_msg *msg, struct babel_iface *ifa);
+
+void babel_show_interfaces(struct proto *P, char *iff);
+void babel_show_neighbors(struct proto *P, char *iff);
+void babel_show_entries(struct proto *P);
+
+/* packets.c */
+void babel_enqueue(union babel_msg *msg, struct babel_iface *ifa);
+void babel_send_unicast(union babel_msg *msg, struct babel_iface *ifa, ip_addr dest);
+int babel_open_socket(struct babel_iface *ifa);
+void babel_send_queue(void *arg);
+
+
+#endif
diff --git a/proto/babel/config.Y b/proto/babel/config.Y
new file mode 100644
index 00000000..e7ce6a93
--- /dev/null
+++ b/proto/babel/config.Y
@@ -0,0 +1,129 @@
+/*
+ *	BIRD -- Babel Configuration
+ *
+ *	Copyright (c) 2015-2016 Toke Hoiland-Jorgensen
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ */
+
+
+
+CF_HDR
+
+#include "proto/babel/babel.h"
+#include "nest/iface.h"
+
+CF_DEFINES
+
+#define BABEL_CFG ((struct babel_config *) this_proto)
+#define BABEL_IFACE ((struct babel_iface_config *) this_ipatt)
+
+CF_DECLS
+
+CF_KEYWORDS(BABEL, METRIC, RXCOST, HELLO, UPDATE, INTERVAL, PORT, WIRED,
+WIRELESS, RX, TX, BUFFER, LENGTH, CHECK, LINK, BABEL_METRIC)
+
+CF_GRAMMAR
+
+CF_ADDTO(proto, babel_proto)
+
+babel_proto_start: proto_start BABEL
+{
+  this_proto = proto_config_new(&proto_babel, $1);
+  init_list(&BABEL_CFG->iface_list);
+};
+
+babel_proto_item:
+   proto_item
+ | INTERFACE babel_iface
+ ;
+
+babel_proto_opts:
+   /* empty */
+ | babel_proto_opts babel_proto_item ';'
+ ;
+
+babel_proto:
+   babel_proto_start proto_name '{' babel_proto_opts '}';
+
+
+babel_iface_start:
+{
+  this_ipatt = cfg_allocz(sizeof(struct babel_iface_config));
+  add_tail(&BABEL_CFG->iface_list, NODE this_ipatt);
+  init_list(&this_ipatt->ipn_list);
+  BABEL_IFACE->port = BABEL_PORT;
+  BABEL_IFACE->type = BABEL_IFACE_TYPE_WIRED;
+  BABEL_IFACE->tx_tos = IP_PREC_INTERNET_CONTROL;
+  BABEL_IFACE->tx_priority = sk_priority_control;
+  BABEL_IFACE->check_link = 1;
+};
+
+
+babel_iface_finish:
+{
+  if (BABEL_IFACE->type == BABEL_IFACE_TYPE_WIRELESS)
+  {
+    if (!BABEL_IFACE->hello_interval)
+      BABEL_IFACE->hello_interval = BABEL_HELLO_INTERVAL_WIRELESS;
+    if (!BABEL_IFACE->rxcost)
+      BABEL_IFACE->rxcost = BABEL_RXCOST_WIRELESS;
+  }
+  else
+  {
+    if (!BABEL_IFACE->hello_interval)
+      BABEL_IFACE->hello_interval = BABEL_HELLO_INTERVAL_WIRED;
+    if (!BABEL_IFACE->rxcost)
+      BABEL_IFACE->rxcost = BABEL_RXCOST_WIRED;
+  }
+
+  if (!BABEL_IFACE->update_interval)
+    BABEL_IFACE->update_interval = BABEL_IFACE->hello_interval*BABEL_UPDATE_INTERVAL_FACTOR;
+  BABEL_IFACE->ihu_interval = BABEL_IFACE->hello_interval*BABEL_IHU_INTERVAL_FACTOR;
+};
+
+
+babel_iface_item:
+ | PORT expr { BABEL_IFACE->port = $2; if (($2<1) || ($2>65535)) cf_error("Invalid port number"); }
+ | RXCOST expr { BABEL_IFACE->rxcost = $2; if (($2<1) || ($2>65535)) cf_error("Invalid rxcost"); }
+ | HELLO INTERVAL expr { BABEL_IFACE->hello_interval = $3; if (($3<1) || ($3>65535)) cf_error("Invalid hello interval"); }
+ | UPDATE INTERVAL expr { BABEL_IFACE->update_interval = $3; if (($3<1) || ($3>65535)) cf_error("Invalid hello interval"); }
+ | TYPE WIRED { BABEL_IFACE->type = BABEL_IFACE_TYPE_WIRED; }
+ | TYPE WIRELESS { BABEL_IFACE->type = BABEL_IFACE_TYPE_WIRELESS; }
+ | RX BUFFER expr { BABEL_IFACE->rx_buffer = $3; if (($3<256) || ($3>65535)) cf_error("RX buffer must be in range 256-65535"); }
+ | TX LENGTH expr { BABEL_IFACE->tx_length = $3; if (($3<256) || ($3>65535)) cf_error("TX length must be in range 256-65535"); }
+ | TX tos { BABEL_IFACE->tx_tos = $2; }
+ | TX PRIORITY expr { BABEL_IFACE->tx_priority = $3; }
+ | CHECK LINK bool { BABEL_IFACE->check_link = $3; }
+ ;
+
+babel_iface_opts:
+   /* empty */
+ | babel_iface_opts babel_iface_item ';'
+ ;
+
+babel_iface_opt_list:
+   /* empty */
+ | '{' babel_iface_opts '}'
+ ;
+
+
+babel_iface:
+  babel_iface_start iface_patt_list_nopx babel_iface_opt_list babel_iface_finish;
+
+CF_ADDTO(dynamic_attr, BABEL_METRIC { $$ = f_new_dynamic_attr(EAF_TYPE_INT | EAF_TEMP, T_INT, EA_BABEL_METRIC); })
+
+CF_CLI_HELP(SHOW BABEL, ..., [[Show information about Babel protocol]]);
+
+CF_CLI(SHOW BABEL INTERFACES, optsym opttext, [<name>] [\"<interface>\"], [[Show information about Babel interfaces]])
+{ babel_show_interfaces(proto_get_named($4, &proto_babel), $5); };
+
+CF_CLI(SHOW BABEL NEIGHBORS, optsym opttext, [<name>] [\"<interface>\"], [[Show information about Babel neighbors]])
+{ babel_show_neighbors(proto_get_named($4, &proto_babel), $5); };
+
+CF_CLI(SHOW BABEL ENTRIES, optsym opttext, [<name>], [[Show information about Babel prefix entries]])
+{ babel_show_entries(proto_get_named($4, &proto_babel)); };
+
+CF_CODE
+
+CF_END
diff --git a/proto/babel/packets.c b/proto/babel/packets.c
new file mode 100644
index 00000000..be47aa75
--- /dev/null
+++ b/proto/babel/packets.c
@@ -0,0 +1,1093 @@
+/*
+ *	BIRD -- The Babel protocol
+ *
+ *	Copyright (c) 2015--2016 Toke Hoiland-Jorgensen
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ *
+ *	This file contains the packet and TLV handling code for the protocol.
+ */
+
+#include "babel.h"
+
+
+struct babel_pkt_header {
+  u8 magic;
+  u8 version;
+  u16 length;
+} PACKED;
+
+struct babel_tlv {
+  u8 type;
+  u8 length;
+  u8 value[0];
+} PACKED;
+
+struct babel_tlv_ack_req {
+  u8 type;
+  u8 length;
+  u16 reserved;
+  u16 nonce;
+  u16 interval;
+} PACKED;
+
+struct babel_tlv_ack {
+  u8 type;
+  u8 length;
+  u16 nonce;
+} PACKED;
+
+struct babel_tlv_hello {
+  u8 type;
+  u8 length;
+  u16 reserved;
+  u16 seqno;
+  u16 interval;
+} PACKED;
+
+struct babel_tlv_ihu {
+  u8 type;
+  u8 length;
+  u8 ae;
+  u8 reserved;
+  u16 rxcost;
+  u16 interval;
+  u8 addr[0];
+} PACKED;
+
+struct babel_tlv_router_id {
+  u8 type;
+  u8 length;
+  u16 reserved;
+  u64 router_id;
+} PACKED;
+
+struct babel_tlv_next_hop {
+  u8 type;
+  u8 length;
+  u8 ae;
+  u8 reserved;
+  u8 addr[0];
+} PACKED;
+
+struct babel_tlv_update {
+  u8 type;
+  u8 length;
+  u8 ae;
+  u8 flags;
+  u8 plen;
+  u8 omitted;
+  u16 interval;
+  u16 seqno;
+  u16 metric;
+  u8 addr[0];
+} PACKED;
+
+struct babel_tlv_route_request {
+  u8 type;
+  u8 length;
+  u8 ae;
+  u8 plen;
+  u8 addr[0];
+} PACKED;
+
+struct babel_tlv_seqno_request {
+  u8 type;
+  u8 length;
+  u8 ae;
+  u8 plen;
+  u16 seqno;
+  u8 hop_count;
+  u8 reserved;
+  u64 router_id;
+  u8 addr[0];
+} PACKED;
+
+
+#define BABEL_FLAG_DEF_PREFIX	0x80
+#define BABEL_FLAG_ROUTER_ID	0x40
+
+
+struct babel_parse_state {
+  struct babel_proto *proto;
+  struct babel_iface *ifa;
+  ip_addr saddr;
+  ip_addr next_hop;
+  u64 router_id;		/* Router ID used in subsequent updates */
+  u8 def_ip6_prefix[16];	/* Implicit IPv6 prefix in network order */
+  u8 def_ip4_prefix[4];		/* Implicit IPv4 prefix in network order */
+  u8 router_id_seen;		/* router_id field is valid */
+  u8 def_ip6_prefix_seen;	/* def_ip6_prefix is valid */
+  u8 def_ip4_prefix_seen;	/* def_ip4_prefix is valid */
+};
+
+enum parse_result {
+  PARSE_SUCCESS,
+  PARSE_ERROR,
+  PARSE_IGNORE,
+};
+
+struct babel_write_state {
+  u64 router_id;
+  u8 router_id_seen;
+//  ip_addr next_hop;
+};
+
+
+#define DROP(DSC,VAL) do { err_dsc = DSC; err_val = VAL; goto drop; } while(0)
+#define DROP1(DSC) do { err_dsc = DSC; goto drop; } while(0)
+#define LOG_PKT(msg, args...) \
+  log_rl(&p->log_pkt_tbf, L_REMOTE "%s: " msg, p->p.name, args)
+
+#define FIRST_TLV(p) ((struct babel_tlv *) (((struct babel_pkt_header *) p) + 1))
+#define NEXT_TLV(t) ((struct babel_tlv *) (((byte *) t) + TLV_LENGTH(t)))
+#define TLV_LENGTH(t) (t->type == BABEL_TLV_PAD1 ? 1 : t->length + sizeof(struct babel_tlv))
+#define TLV_OPT_LENGTH(t) (t->length + sizeof(struct babel_tlv) - sizeof(*t))
+#define TLV_HDR(tlv,t,l) ({ tlv->type = t; tlv->length = l - sizeof(struct babel_tlv); })
+#define TLV_HDR0(tlv,t) TLV_HDR(tlv, t, tlv_data[t].min_length)
+
+
+static inline u16
+get_time16(const void *p)
+{
+  u16 v = get_u16(p) / BABEL_TIME_UNITS;
+  return MAX(1, v);
+}
+
+static inline void
+put_time16(void *p, u16 v)
+{
+  put_u16(p, v * BABEL_TIME_UNITS);
+}
+
+static inline ip6_addr
+get_ip6_px(const void *p, int plen)
+{
+  ip6_addr addr = IPA_NONE;
+  memcpy(&addr, p, (plen + 7) / 8);
+  return ip6_ntoh(addr);
+}
+
+static inline void
+put_ip6_px(void *p, ip6_addr addr, int plen)
+{
+  addr = ip6_hton(addr);
+  memcpy(p, &addr, (plen + 7) / 8);
+}
+
+static inline ip6_addr
+get_ip6_ll(const void *p)
+{
+  return ip6_build(0xfe800000, 0, get_u32(p+0), get_u32(p+4));
+}
+
+static inline void
+put_ip6_ll(void *p, ip6_addr addr)
+{
+  put_u32(p+0, _I2(addr));
+  put_u32(p+4, _I3(addr));
+}
+
+
+/*
+ *	TLV read/write functions
+ */
+
+static int babel_read_ack_req(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
+static int babel_read_hello(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
+static int babel_read_ihu(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
+static int babel_read_router_id(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
+static int babel_read_next_hop(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
+static int babel_read_update(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
+static int babel_read_route_request(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
+static int babel_read_seqno_request(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
+
+static int babel_write_ack(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, int max_len);
+static int babel_write_hello(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, int max_len);
+static int babel_write_ihu(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, int max_len);
+static int babel_write_update(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, int max_len);
+static int babel_write_route_request(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, int max_len);
+static int babel_write_seqno_request(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, int max_len);
+
+struct babel_tlv_data {
+  u8 min_length;
+  int (*read_tlv)(struct babel_tlv *hdr, union babel_msg *m, struct babel_parse_state *state);
+  int (*write_tlv)(struct babel_tlv *hdr, union babel_msg *m, struct babel_write_state *state, int max_len);
+  void (*handle_tlv)(union babel_msg *m, struct babel_iface *ifa);
+};
+
+const static struct babel_tlv_data tlv_data[BABEL_TLV_MAX] = {
+  [BABEL_TLV_ACK_REQ] = {
+    sizeof(struct babel_tlv_ack_req),
+    babel_read_ack_req,
+    NULL,
+    babel_handle_ack_req
+  },
+  [BABEL_TLV_ACK] = {
+    sizeof(struct babel_tlv_ack),
+    NULL,
+    babel_write_ack,
+    NULL
+  },
+  [BABEL_TLV_HELLO] = {
+    sizeof(struct babel_tlv_hello),
+    babel_read_hello,
+    babel_write_hello,
+    babel_handle_hello
+  },
+  [BABEL_TLV_IHU] = {
+    sizeof(struct babel_tlv_ihu),
+    babel_read_ihu,
+    babel_write_ihu,
+    babel_handle_ihu
+  },
+  [BABEL_TLV_ROUTER_ID] = {
+    sizeof(struct babel_tlv_router_id),
+    babel_read_router_id,
+    NULL,
+    NULL
+  },
+  [BABEL_TLV_NEXT_HOP] = {
+    sizeof(struct babel_tlv_next_hop),
+    babel_read_next_hop,
+    NULL,
+    NULL
+  },
+  [BABEL_TLV_UPDATE] = {
+    sizeof(struct babel_tlv_update),
+    babel_read_update,
+    babel_write_update,
+    babel_handle_update
+  },
+  [BABEL_TLV_ROUTE_REQUEST] = {
+    sizeof(struct babel_tlv_route_request),
+    babel_read_route_request,
+    babel_write_route_request,
+    babel_handle_route_request
+  },
+  [BABEL_TLV_SEQNO_REQUEST] = {
+    sizeof(struct babel_tlv_seqno_request),
+    babel_read_seqno_request,
+    babel_write_seqno_request,
+    babel_handle_seqno_request
+  },
+};
+
+static int
+babel_read_ack_req(struct babel_tlv *hdr, union babel_msg *m,
+		   struct babel_parse_state *state)
+{
+  struct babel_tlv_ack_req *tlv = (void *) hdr;
+  struct babel_msg_ack_req *msg = &m->ack_req;
+
+  msg->type = BABEL_TLV_ACK_REQ;
+  msg->nonce = get_u16(&tlv->nonce);
+  msg->interval = get_time16(&tlv->interval);
+  msg->sender = state->saddr;
+
+  if (!msg->interval)
+    return PARSE_ERROR;
+
+  return PARSE_SUCCESS;
+}
+
+static int
+babel_write_ack(struct babel_tlv *hdr, union babel_msg *m,
+                struct babel_write_state *state, int max_len)
+{
+  struct babel_tlv_ack *tlv = (void *) hdr;
+  struct babel_msg_ack *msg = &m->ack;
+
+  TLV_HDR0(tlv, BABEL_TLV_ACK);
+  put_u16(&tlv->nonce, msg->nonce);
+
+  return sizeof(struct babel_tlv_ack);
+}
+
+static int
+babel_read_hello(struct babel_tlv *hdr, union babel_msg *m,
+                 struct babel_parse_state *state)
+{
+  struct babel_tlv_hello *tlv = (void *) hdr;
+  struct babel_msg_hello *msg = &m->hello;
+
+  msg->type = BABEL_TLV_HELLO;
+  msg->seqno = get_u16(&tlv->seqno);
+  msg->interval = get_time16(&tlv->interval);
+  msg->sender = state->saddr;
+
+  return PARSE_SUCCESS;
+}
+
+static int
+babel_write_hello(struct babel_tlv *hdr, union babel_msg *m,
+                  struct babel_write_state *state, int max_len)
+{
+  struct babel_tlv_hello *tlv = (void *) hdr;
+  struct babel_msg_hello *msg = &m->hello;
+
+  TLV_HDR0(tlv, BABEL_TLV_HELLO);
+  put_u16(&tlv->seqno, msg->seqno);
+  put_time16(&tlv->interval, msg->interval);
+
+  return sizeof(struct babel_tlv_hello);
+}
+
+static int
+babel_read_ihu(struct babel_tlv *hdr, union babel_msg *m,
+               struct babel_parse_state *state)
+{
+  struct babel_tlv_ihu *tlv = (void *) hdr;
+  struct babel_msg_ihu *msg = &m->ihu;
+
+  msg->type = BABEL_TLV_IHU;
+  msg->ae = tlv->ae;
+  msg->rxcost = get_u16(&tlv->rxcost);
+  msg->interval = get_time16(&tlv->interval);
+  msg->addr = IPA_NONE;
+  msg->sender = state->saddr;
+
+  if (msg->ae >= BABEL_AE_MAX)
+    return PARSE_IGNORE;
+
+  // We handle link-local IPs. In every other case, the addr field will be 0 but
+  // validation will succeed. The handler takes care of these cases.
+  if (msg->ae == BABEL_AE_IP6_LL)
+  {
+    if (TLV_OPT_LENGTH(tlv) < 8)
+      return PARSE_ERROR;
+
+    msg->addr = ipa_from_ip6(get_ip6_ll(&tlv->addr));
+  }
+
+  return PARSE_SUCCESS;
+}
+
+static int
+babel_write_ihu(struct babel_tlv *hdr, union babel_msg *m,
+                struct babel_write_state *state, int max_len)
+{
+  struct babel_tlv_ihu *tlv = (void *) hdr;
+  struct babel_msg_ihu *msg = &m->ihu;
+
+  if (ipa_is_link_local(msg->addr) && max_len < sizeof(struct babel_tlv_ihu) + 8)
+    return 0;
+
+  TLV_HDR0(tlv, BABEL_TLV_IHU);
+  put_u16(&tlv->rxcost, msg->rxcost);
+  put_time16(&tlv->interval, msg->interval);
+
+  if (!ipa_is_link_local(msg->addr))
+  {
+    tlv->ae = BABEL_AE_WILDCARD;
+    return sizeof(struct babel_tlv_ihu);
+  }
+  put_ip6_ll(&tlv->addr, msg->addr);
+  tlv->ae = BABEL_AE_IP6_LL;
+  hdr->length += 8;
+  return sizeof(struct babel_tlv_ihu) + 8;
+}
+
+static int
+babel_read_router_id(struct babel_tlv *hdr, union babel_msg *m UNUSED,
+                     struct babel_parse_state *state)
+{
+  struct babel_tlv_router_id *tlv = (void *) hdr;
+
+  state->router_id = get_u64(&tlv->router_id);
+  state->router_id_seen = 1;
+
+  return PARSE_IGNORE;
+}
+
+/* This is called directly from babel_write_update() */
+static int
+babel_write_router_id(struct babel_tlv *hdr, u64 router_id,
+		      struct babel_write_state *state, int max_len UNUSED)
+{
+  struct babel_tlv_router_id *tlv = (void *) hdr;
+
+  /* We still assume that first min_length bytes are available and zeroed */
+
+  TLV_HDR0(tlv, BABEL_TLV_ROUTER_ID);
+  put_u64(&tlv->router_id, router_id);
+
+  state->router_id = router_id;
+  state->router_id_seen = 1;
+
+  return sizeof(struct babel_tlv_router_id);
+}
+
+static int
+babel_read_next_hop(struct babel_tlv *hdr, union babel_msg *m UNUSED,
+                    struct babel_parse_state *state)
+{
+  struct babel_tlv_next_hop *tlv = (void *) hdr;
+
+  switch (tlv->ae)
+  {
+  case BABEL_AE_WILDCARD:
+    return PARSE_ERROR;
+
+  case BABEL_AE_IP4:
+    /* TODO */
+    return PARSE_IGNORE;
+
+  case BABEL_AE_IP6:
+    if (TLV_OPT_LENGTH(tlv) < sizeof(ip6_addr))
+      return PARSE_ERROR;
+
+    state->next_hop = ipa_from_ip6(get_ip6(&tlv->addr));
+    return PARSE_IGNORE;
+
+  case BABEL_AE_IP6_LL:
+    if (TLV_OPT_LENGTH(tlv) < 8)
+      return PARSE_ERROR;
+
+    state->next_hop = ipa_from_ip6(get_ip6_ll(&tlv->addr));
+    return PARSE_IGNORE;
+
+  default:
+    return PARSE_IGNORE;
+  }
+
+  return PARSE_IGNORE;
+}
+
+static int
+babel_read_update(struct babel_tlv *hdr, union babel_msg *m,
+                  struct babel_parse_state *state)
+{
+  struct babel_tlv_update *tlv = (void *) hdr;
+  struct babel_msg_update *msg = &m->update;
+
+  msg->type = BABEL_TLV_UPDATE;
+  msg->ae = tlv->ae;
+  msg->interval = get_time16(&tlv->interval);
+  msg->seqno = get_u16(&tlv->seqno);
+  msg->metric = get_u16(&tlv->metric);
+
+  /* Length of received prefix data without omitted part */
+  int len = (tlv->plen + 7)/8 - (int) tlv->omitted;
+  u8 buf[16] = {};
+
+  if ((len < 0) || (len > TLV_OPT_LENGTH(tlv)))
+    return PARSE_ERROR;
+
+  switch (tlv->ae)
+  {
+  case BABEL_AE_WILDCARD:
+    if (tlv->plen > 0)
+      return PARSE_ERROR;
+
+    msg->prefix = IPA_NONE;
+    break;
+
+  case BABEL_AE_IP4:
+    /* TODO */
+    return PARSE_IGNORE;
+
+  case BABEL_AE_IP6:
+    if (tlv->plen > MAX_PREFIX_LENGTH)
+      return PARSE_ERROR;
+
+    /* Cannot omit data if there is no saved prefix */
+    if (tlv->omitted && !state->def_ip6_prefix_seen)
+      return PARSE_ERROR;
+
+    /* Merge saved prefix and received prefix parts */
+    memcpy(buf, state->def_ip6_prefix, tlv->omitted);
+    memcpy(buf + tlv->omitted, tlv->addr, len);
+
+    msg->plen = tlv->plen;
+    msg->prefix = ipa_from_ip6(get_ip6(buf));
+
+    if (tlv->flags & BABEL_FLAG_DEF_PREFIX)
+    {
+      put_ip6(state->def_ip6_prefix, msg->prefix);
+      state->def_ip6_prefix_seen = 1;
+    }
+
+    if (tlv->flags & BABEL_FLAG_ROUTER_ID)
+    {
+      state->router_id = ((u64) _I2(msg->prefix)) << 32 | _I3(msg->prefix);
+      state->router_id_seen = 1;
+    }
+    break;
+
+  case BABEL_AE_IP6_LL:
+    /* ??? */
+    return PARSE_IGNORE;
+
+  default:
+    return PARSE_IGNORE;
+  }
+
+  if (!state->router_id_seen)
+  {
+    DBG("Babel: No router ID seen before update\n");
+    return PARSE_ERROR;
+  }
+
+  msg->router_id = state->router_id;
+  msg->next_hop = state->next_hop;
+  msg->sender = state->saddr;
+
+  return PARSE_SUCCESS;
+}
+
+static int
+babel_write_update(struct babel_tlv *hdr, union babel_msg *m,
+                   struct babel_write_state *state, int max_len)
+{
+  struct babel_tlv_update *tlv = (void *) hdr;
+  struct babel_msg_update *msg = &m->update;
+  int len0 = 0;
+
+  /*
+   * When needed, we write Router-ID TLV before Update TLV and return size of
+   * both of them. There is enough space for the Router-ID TLV, because
+   * sizeof(struct babel_tlv_router_id) == sizeof(struct babel_tlv_update).
+   */
+  if (!state->router_id_seen || (msg->router_id != state->router_id))
+  {
+    len0 = babel_write_router_id(hdr, msg->router_id, state, max_len);
+    tlv = (struct babel_tlv_update *) NEXT_TLV(tlv);
+  }
+
+  int len = sizeof(struct babel_tlv_update) + (msg->plen + 7)/8;
+
+  if (len0 + len > max_len)
+    return 0;
+
+  memset(tlv, 0, sizeof(struct babel_tlv_update));
+  TLV_HDR(tlv, BABEL_TLV_UPDATE, len);
+  tlv->ae = BABEL_AE_IP6;
+  tlv->plen = msg->plen;
+  put_time16(&tlv->interval, msg->interval);
+  put_u16(&tlv->seqno, msg->seqno);
+  put_u16(&tlv->metric, msg->metric);
+  put_ip6_px(tlv->addr, msg->prefix, msg->plen);
+
+  return len0 + len;
+}
+
+static int
+babel_read_route_request(struct babel_tlv *hdr, union babel_msg *m,
+                         struct babel_parse_state *state)
+{
+  struct babel_tlv_route_request *tlv = (void *) hdr;
+  struct babel_msg_route_request *msg = &m->route_request;
+
+  msg->type = BABEL_TLV_ROUTE_REQUEST;
+
+  switch (tlv->ae)
+  {
+  case BABEL_AE_WILDCARD:
+    /* Wildcard requests must have plen 0 */
+    if (tlv->plen > 0)
+      return PARSE_ERROR;
+
+    msg->full = 1;
+    return PARSE_SUCCESS;
+
+  case BABEL_AE_IP4:
+    /* TODO */
+    return PARSE_IGNORE;
+
+  case BABEL_AE_IP6:
+    if (tlv->plen > MAX_PREFIX_LENGTH)
+      return PARSE_ERROR;
+
+    if (TLV_OPT_LENGTH(tlv) < (tlv->plen + 7)/8)
+      return PARSE_ERROR;
+
+    msg->plen = tlv->plen;
+    msg->prefix = get_ip6_px(tlv->addr, tlv->plen);
+    return PARSE_SUCCESS;
+
+  case BABEL_AE_IP6_LL:
+    return PARSE_ERROR;
+
+  default:
+    return PARSE_IGNORE;
+  }
+
+  return PARSE_IGNORE;
+}
+
+static int
+babel_write_route_request(struct babel_tlv *hdr, union babel_msg *m,
+			  struct babel_write_state *state, int max_len)
+{
+  struct babel_tlv_route_request *tlv = (void *) hdr;
+  struct babel_msg_route_request *msg = &m->route_request;
+
+  int len = sizeof(struct babel_tlv_route_request) + (msg->plen + 7)/8;
+
+  if (len > max_len)
+    return 0;
+
+  TLV_HDR(tlv, BABEL_TLV_ROUTE_REQUEST, len);
+
+  if (msg->full)
+  {
+    tlv->ae = BABEL_AE_WILDCARD;
+    tlv->plen = 0;
+  }
+  else
+  {
+    tlv->ae = BABEL_AE_IP6;
+    tlv->plen = msg->plen;
+    put_ip6_px(tlv->addr, msg->prefix, msg->plen);
+  }
+
+  return len;
+}
+
+static int
+babel_read_seqno_request(struct babel_tlv *hdr, union babel_msg *m,
+                         struct babel_parse_state *state)
+{
+  struct babel_tlv_seqno_request *tlv = (void *) hdr;
+  struct babel_msg_seqno_request *msg = &m->seqno_request;
+
+  msg->type = BABEL_TLV_SEQNO_REQUEST;
+  msg->seqno = get_u16(&tlv->seqno);
+  msg->hop_count = tlv->hop_count;
+  msg->router_id = get_u64(&tlv->router_id);
+  msg->sender = state->saddr;
+
+  if (tlv->hop_count == 0)
+    return PARSE_ERROR;
+
+  switch (tlv->ae)
+  {
+  case BABEL_AE_WILDCARD:
+    return PARSE_ERROR;
+
+  case BABEL_AE_IP4:
+    /* TODO */
+    return PARSE_IGNORE;
+
+  case BABEL_AE_IP6:
+    if (tlv->plen > MAX_PREFIX_LENGTH)
+      return PARSE_ERROR;
+
+    if (TLV_OPT_LENGTH(tlv) < (tlv->plen + 7)/8)
+      return PARSE_ERROR;
+
+    msg->plen = tlv->plen;
+    msg->prefix = get_ip6_px(tlv->addr, tlv->plen);
+    return PARSE_SUCCESS;
+
+  case BABEL_AE_IP6_LL:
+    return PARSE_ERROR;
+
+  default:
+    return PARSE_IGNORE;
+  }
+
+  return PARSE_IGNORE;
+}
+
+static int
+babel_write_seqno_request(struct babel_tlv *hdr, union babel_msg *m,
+			  struct babel_write_state *state, int max_len)
+{
+  struct babel_tlv_seqno_request *tlv = (void *) hdr;
+  struct babel_msg_seqno_request *msg = &m->seqno_request;
+
+  int len = sizeof(struct babel_tlv_seqno_request) + (msg->plen + 7)/8;
+
+  if (len > max_len)
+    return 0;
+
+  TLV_HDR(tlv, BABEL_TLV_SEQNO_REQUEST, len);
+  tlv->ae = BABEL_AE_IP6;
+  tlv->plen = msg->plen;
+  put_u16(&tlv->seqno, msg->seqno);
+  tlv->hop_count = msg->hop_count;
+  put_u64(&tlv->router_id, msg->router_id);
+  put_ip6_px(tlv->addr, msg->prefix, msg->plen);
+
+  return len;
+}
+
+static inline int
+babel_read_tlv(struct babel_tlv *hdr,
+               union babel_msg *msg,
+               struct babel_parse_state *state)
+{
+  if ((hdr->type <= BABEL_TLV_PADN) ||
+      (hdr->type >= BABEL_TLV_MAX) ||
+      !tlv_data[hdr->type].read_tlv)
+    return PARSE_IGNORE;
+
+  if (TLV_LENGTH(hdr) < tlv_data[hdr->type].min_length)
+    return PARSE_ERROR;
+
+  memset(msg, 0, sizeof(*msg));
+  return tlv_data[hdr->type].read_tlv(hdr, msg, state);
+}
+
+static int
+babel_write_tlv(struct babel_tlv *hdr,
+		union babel_msg *msg,
+		struct babel_write_state *state,
+		int max_len)
+{
+  if ((msg->type <= BABEL_TLV_PADN) ||
+      (msg->type >= BABEL_TLV_MAX) ||
+      !tlv_data[msg->type].write_tlv)
+    return 0;
+
+  if (tlv_data[msg->type].min_length > max_len)
+    return 0;
+
+  memset(hdr, 0, tlv_data[msg->type].min_length);
+  return tlv_data[msg->type].write_tlv(hdr, msg, state, max_len);
+}
+
+
+/*
+ *	Packet RX/TX functions
+ */
+
+static int
+babel_send_to(struct babel_iface *ifa, ip_addr dest)
+{
+  sock *sk = ifa->sk;
+  struct babel_pkt_header *hdr = (void *) sk->tbuf;
+  int len = get_u16(&hdr->length) + sizeof(struct babel_pkt_header);
+
+  DBG("Babel: Sending %d bytes to %I\n", len, dest);
+  return sk_send_to(sk, len, dest, 0);
+}
+
+/**
+ * babel_write_queue - Write a TLV queue to a transmission buffer
+ * @ifa: Interface holding the transmission buffer
+ * @queue: TLV queue to write (containing internal-format TLVs)
+ *
+ * This function writes a packet to the interface transmission buffer with as
+ * many TLVs from the &queue as will fit in the buffer. It returns the number of
+ * bytes written (NOT counting the packet header). The function is called by
+ * babel_send_queue() and babel_send_unicast() to construct packets for
+ * transmission, and uses per-TLV helper functions to convert the
+ * internal-format TLVs to their wire representations.
+ *
+ * The TLVs in the queue are freed after they are written to the buffer.
+ */
+static int
+babel_write_queue(struct babel_iface *ifa, list *queue)
+{
+  struct babel_proto *p = ifa->proto;
+  struct babel_write_state state = {};
+
+  if (EMPTY_LIST(*queue))
+    return 0;
+
+  byte *pos = ifa->sk->tbuf;
+  byte *end = pos + ifa->tx_length;
+
+  struct babel_pkt_header *pkt = (void *) pos;
+  pkt->magic = BABEL_MAGIC;
+  pkt->version = BABEL_VERSION;
+  pkt->length = 0;
+  pos += sizeof(struct babel_pkt_header);
+
+  struct babel_msg_node *msg;
+  WALK_LIST_FIRST(msg, *queue)
+  {
+    int len = babel_write_tlv((struct babel_tlv *) pos, &msg->msg, &state, end - pos);
+
+    if (!len)
+      break;
+
+    pos += len;
+    rem_node(NODE msg);
+    sl_free(p->msg_slab, msg);
+  }
+
+  int plen = pos - (byte *) pkt;
+  put_u16(&pkt->length, plen - sizeof(struct babel_pkt_header));
+
+  return plen;
+}
+
+void
+babel_send_queue(void *arg)
+{
+  struct babel_iface *ifa = arg;
+  while ((babel_write_queue(ifa, &ifa->msg_queue) > 0) &&
+	 (babel_send_to(ifa, IP6_BABEL_ROUTERS) > 0));
+}
+
+static inline void
+babel_kick_queue(struct babel_iface *ifa)
+{
+  /*
+   * Only schedule send event if there is not already data in the socket buffer.
+   * Otherwise we may overwrite the data already in the buffer.
+   */
+
+  if ((ifa->sk->tpos == ifa->sk->tbuf) && !ev_active(ifa->send_event))
+    ev_schedule(ifa->send_event);
+}
+
+/**
+ * babel_send_unicast - send a single TLV via unicast to a destination
+ * @msg: TLV to send
+ * @ifa: Interface to send via
+ * @dest: Destination of the TLV
+ *
+ * This function is used to send a single TLV via unicast to a designated
+ * receiver. This is used for replying to certain incoming requests, and for
+ * sending unicast requests to refresh routes before they expire.
+ */
+void
+babel_send_unicast(union babel_msg *msg, struct babel_iface *ifa, ip_addr dest)
+{
+  struct babel_proto *p = ifa->proto;
+  struct babel_msg_node *msgn = sl_alloc(p->msg_slab);
+  list queue;
+
+  msgn->msg = *msg;
+  init_list(&queue);
+  add_tail(&queue, NODE msgn);
+  babel_write_queue(ifa, &queue);
+  babel_send_to(ifa, dest);
+
+  /* We could overwrite waiting packet here, we may have to kick TX queue */
+  if (!EMPTY_LIST(ifa->msg_queue))
+    babel_kick_queue(ifa);
+}
+
+/**
+ * babel_enqueue - enqueue a TLV for transmission on an interface
+ * @msg: TLV to enqueue (in internal TLV format)
+ * @ifa: Interface to enqueue to
+ *
+ * This function is called to enqueue a TLV for subsequent transmission on an
+ * interface. The transmission event is triggered whenever a TLV is enqueued;
+ * this ensures that TLVs will be transmitted in a timely manner, but that TLVs
+ * which are enqueued in rapid succession can be transmitted together in one
+ * packet.
+ */
+void
+babel_enqueue(union babel_msg *msg, struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+  struct babel_msg_node *msgn = sl_alloc(p->msg_slab);
+  msgn->msg = *msg;
+  add_tail(&ifa->msg_queue, NODE msgn);
+  babel_kick_queue(ifa);
+}
+
+/**
+ * babel_process_packet - process incoming data packet
+ * @pkt: Pointer to the packet data
+ * @len: Length of received packet
+ * @saddr: Address of packet sender
+ * @ifa: Interface packet was received on.
+ *
+ * This function is the main processing hook of incoming Babel packets. It
+ * checks that the packet header is well-formed, then processes the TLVs
+ * contained in the packet. This is done in two passes: First all TLVs are
+ * parsed into the internal TLV format. If a TLV parser fails, processing of the
+ * rest of the packet is aborted.
+ *
+ * After the parsing step, the TLV handlers are called for each parsed TLV in
+ * order.
+ */
+static void
+babel_process_packet(struct babel_pkt_header *pkt, int len,
+                     ip_addr saddr, struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+  struct babel_tlv *tlv;
+  struct babel_msg_node *msg;
+  list msgs;
+  int res;
+
+  int plen = sizeof(struct babel_pkt_header) + get_u16(&pkt->length);
+  byte *pos;
+  byte *end = (byte *)pkt + plen;
+
+  struct babel_parse_state state = {
+    .proto	= p,
+    .ifa	= ifa,
+    .saddr	= saddr,
+    .next_hop	= saddr,
+  };
+
+  if ((pkt->magic != BABEL_MAGIC) || (pkt->version != BABEL_VERSION))
+  {
+    TRACE(D_PACKETS, "Strange packet from %I via %s - magic %d version %d",
+	  saddr, ifa->iface->name, pkt->magic, pkt->version);
+    return;
+  }
+
+  if (plen > len)
+  {
+    LOG_PKT("Bad packet from %I via %s - %s (%u)",
+	    saddr, ifa->iface->name, "length mismatch", plen);
+    return;
+  }
+
+  TRACE(D_PACKETS, "Packet received from %I via %s",
+        saddr, ifa->iface->name);
+
+  init_list(&msgs);
+
+  /* First pass through the packet TLV by TLV, parsing each into internal data
+     structures. */
+  for (tlv = FIRST_TLV(pkt);
+       (byte *)tlv < end;
+       tlv = NEXT_TLV(tlv))
+  {
+    /* Ugly special case */
+    if (tlv->type == BABEL_TLV_PAD1)
+      continue;
+
+    /* The end of the common TLV header */
+    pos = (byte *)tlv + sizeof(struct babel_tlv);
+    if ((pos > end) || (pos + tlv->length > end))
+    {
+      LOG_PKT("Bad TLV from %I via %s type %d pos %d - framing error",
+	      saddr, ifa->iface->name, tlv->type, (byte *)tlv - (byte *)pkt);
+      break;
+    }
+
+    msg = sl_alloc(p->msg_slab);
+    res = babel_read_tlv(tlv, &msg->msg, &state);
+    if (res == PARSE_SUCCESS)
+    {
+      add_tail(&msgs, NODE msg);
+    }
+    else if (res == PARSE_IGNORE)
+    {
+      DBG("Babel: Ignoring TLV of type %d\n", tlv->type);
+      sl_free(p->msg_slab, msg);
+    }
+    else /* PARSE_ERROR */
+    {
+      LOG_PKT("Bad TLV from %I via %s type %d pos %d - parse error",
+	      saddr, ifa->iface->name, tlv->type, (byte *)tlv - (byte *)pkt);
+      sl_free(p->msg_slab, msg);
+      break;
+    }
+  }
+
+  /* Parsing done, handle all parsed TLVs */
+  WALK_LIST_FIRST(msg, msgs)
+  {
+    if (tlv_data[msg->msg.type].handle_tlv)
+      tlv_data[msg->msg.type].handle_tlv(&msg->msg, ifa);
+    rem_node(NODE msg);
+    sl_free(p->msg_slab, msg);
+  }
+}
+
+static void
+babel_err_hook(sock *sk, int err)
+{
+  struct babel_iface *ifa = sk->data;
+  struct babel_proto *p = ifa->proto;
+
+  log(L_ERR "%s: Socket error on %s: %M", p->p.name, ifa->iface->name, err);
+  /* FIXME: Drop queued TLVs here? */
+}
+
+
+static void
+babel_tx_hook(sock *sk)
+{
+  struct babel_iface *ifa = sk->data;
+
+  DBG("Babel: TX hook called (iface %s, src %I, dst %I)\n",
+      sk->iface->name, sk->saddr, sk->daddr);
+
+  babel_send_queue(ifa);
+}
+
+
+static int
+babel_rx_hook(sock *sk, int len)
+{
+  struct babel_iface *ifa = sk->data;
+  struct babel_proto *p = ifa->proto;
+  const char *err_dsc = NULL;
+  uint err_val = 0;
+
+  if (sk->lifindex != ifa->iface->index)
+    return 1;
+
+  DBG("Babel: RX hook called (iface %s, src %I, dst %I)\n",
+      sk->iface->name, sk->faddr, sk->laddr);
+
+  /* Silently ignore my own packets */
+  if (ipa_equal(ifa->iface->addr->ip, sk->faddr))
+    return 1;
+
+  if (!ipa_is_link_local(sk->faddr))
+    DROP1("wrong src address");
+
+  if (sk->fport != ifa->cf->port)
+    DROP("wrong src port", sk->fport);
+
+  if (len < sizeof(struct babel_pkt_header))
+    DROP("too short", len);
+
+  if (sk->flags & SKF_TRUNCATED)
+    DROP("truncated", len);
+
+  babel_process_packet((struct babel_pkt_header *) sk->rbuf, len, sk->faddr, ifa);
+  return 1;
+
+drop:
+  LOG_PKT("Bad packet from %I via %s - %s (%u)",
+	  sk->faddr, sk->iface->name, err_dsc, err_val);
+  return 1;
+}
+
+int
+babel_open_socket(struct babel_iface *ifa)
+{
+  struct babel_proto *p = ifa->proto;
+
+  sock *sk;
+  sk = sk_new(ifa->pool);
+  sk->type = SK_UDP;
+  sk->sport = ifa->cf->port;
+  sk->dport = ifa->cf->port;
+  sk->iface = ifa->iface;
+
+  sk->rx_hook = babel_rx_hook;
+  sk->tx_hook = babel_tx_hook;
+  sk->err_hook = babel_err_hook;
+  sk->data = ifa;
+
+  sk->tos = ifa->cf->tx_tos;
+  sk->priority = ifa->cf->tx_priority;
+  sk->ttl = 1;
+  sk->flags = SKF_LADDR_RX;
+
+  if (sk_open(sk) < 0)
+    goto err;
+
+  if (sk_setup_multicast(sk) < 0)
+    goto err;
+
+  if (sk_join_group(sk, IP6_BABEL_ROUTERS) < 0)
+    goto err;
+
+  ifa->sk = sk;
+  return 1;
+
+err:
+  sk_log_error(sk, p->p.name);
+  rfree(sk);
+  return 0;
+}
diff --git a/sysdep/autoconf.h.in b/sysdep/autoconf.h.in
index a9e46e27..c73270c3 100644
--- a/sysdep/autoconf.h.in
+++ b/sysdep/autoconf.h.in
@@ -43,6 +43,7 @@
 #undef CONFIG_BGP
 #undef CONFIG_OSPF
 #undef CONFIG_PIPE
+#undef CONFIG_BABEL
 
 /* We use multithreading */
 #undef USE_PTHREADS