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.

1 files changed, 2055 insertions, 0 deletions

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
+};