L3VPN: BGP/MPLS VPNs using MPLS backbone

The L3VPN protocol implements RFC 4364 BGP/MPLS VPNs using MPLS backbone.
It works similarly to pipe. It connects IP table (one per VRF) with (global)
VPN table. Routes passed from VPN table to IP table are stripped of RD and
filtered by import targets, routes passed in the other direction are extended
with RD, MPLS labels and export targets in extended communities. A separate
MPLS channel is used to announce MPLS routes for the labels.

1 files changed, 476 insertions, 0 deletions

diff --git a/proto/l3vpn/l3vpn.c b/proto/l3vpn/l3vpn.c
new file mode 100644
index 00000000..3bf0df48
--- /dev/null
+++ b/proto/l3vpn/l3vpn.c
@@ -0,0 +1,476 @@
+/*
+ *	BIRD -- BGP/MPLS IP Virtual Private Networks (L3VPN)
+ *
+ *	(c) 2022 Ondrej Zajicek <santiago@crfreenet.org>
+ *	(c) 2022 CZ.NIC z.s.p.o.
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ */
+
+/**
+ * DOC: L3VPN
+ *
+ * The L3VPN protocol implements RFC 4364 BGP/MPLS VPNs using MPLS backbone.
+ * It works similarly to pipe. It connects IP table (one per VRF) with (global)
+ * VPN table. Routes passed from VPN table to IP table are stripped of RD and
+ * filtered by import targets, routes passed in the other direction are extended
+ * with RD, MPLS labels and export targets in extended communities. Separate
+ * MPLS channel is used to announce MPLS routes for the labels.
+ *
+ * Note that in contrast to the pipe protocol, L3VPN protocol has both IPv4 and
+ * IPv6 channels in one instance, Also both IP and VPN channels are presented to
+ * users as separate channels, although that will change in the future.
+ *
+ * The L3VPN protocol has different default preferences on IP and VPN sides.
+ * The reason is that in import direction (VPN->IP) routes should have lower
+ * preferences that ones received from local CE (perhaps by EBGP), while in
+ * export direction (IP->VPN) routes should have higher preferences that ones
+ * received from remote PEs (by IBGP).
+ *
+ * Supported standards:
+ * RFC 4364 - BGP/MPLS IP Virtual Private Networks (L3VPN)
+ */
+
+#undef LOCAL_DEBUG
+
+#include "nest/bird.h"
+#include "nest/iface.h"
+#include "nest/protocol.h"
+#include "nest/route.h"
+#include "nest/mpls.h"
+#include "nest/cli.h"
+#include "conf/conf.h"
+#include "filter/filter.h"
+#include "filter/data.h"
+#include "lib/string.h"
+
+#include "l3vpn.h"
+
+#include "proto/bgp/bgp.h"
+
+/*
+ * TODO:
+ * - import/export target reconfiguration
+ * - check for simple nodes in export route
+ * - replace pair of channels with shared channel for one address family
+ * - improve route comparisons in VRFs
+ * - optional import/export target all
+ * - optional support for route origins
+ * - optional automatic assignment of RDs
+ * - MPLS-in-IP encapsulation
+ */
+
+#define EA_BGP_NEXT_HOP		EA_CODE(PROTOCOL_BGP, BA_NEXT_HOP)
+#define EA_BGP_EXT_COMMUNITY	EA_CODE(PROTOCOL_BGP, BA_EXT_COMMUNITY)
+#define EA_BGP_MPLS_LABEL_STACK	EA_CODE(PROTOCOL_BGP, BA_MPLS_LABEL_STACK)
+
+static inline const struct adata * ea_get_adata(ea_list *e, uint id)
+{ eattr *a = ea_find(e, id); return a ? a->u.ptr : &null_adata; }
+
+static inline int
+mpls_valid_nexthop(const rta *a)
+{
+  /* MPLS does not support special blackhole targets */
+  if (a->dest != RTD_UNICAST)
+    return 0;
+
+  /* MPLS does not support ARP / neighbor discovery */
+  for (const struct nexthop *nh = &a->nh; nh ; nh = nh->next)
+    if (ipa_zero(nh->gw) && (nh->iface->flags & IF_MULTIACCESS))
+      return 0;
+
+  return 1;
+}
+
+static int
+l3vpn_import_targets(struct l3vpn_proto *p, const struct adata *list)
+{
+  return (p->import_target_one) ?
+    ec_set_contains(list, p->import_target->from.val.ec) :
+    eclist_match_set(list, p->import_target);
+}
+
+static struct adata *
+l3vpn_export_targets(struct l3vpn_proto *p, const struct adata *src)
+{
+  u32 *s = int_set_get_data(src);
+  int len = int_set_get_size(src);
+
+  struct adata *dst = lp_alloc(tmp_linpool, sizeof(struct adata) + (len + p->export_target_length) * sizeof(u32));
+  u32 *d = int_set_get_data(dst);
+  int end = 0;
+
+  for (int i = 0; i < len; i += 2)
+  {
+    /* Remove existing route targets */
+    uint type = s[i] >> 16;
+    if (ec_type_is_rt(type))
+      continue;
+
+    d[end++] = s[i];
+    d[end++] = s[i+1];
+  }
+
+  /* Add new route targets */
+  memcpy(d + end, p->export_target_data, p->export_target_length * sizeof(u32));
+  end += p->export_target_length;
+
+  /* Set length */
+  dst->length = end * sizeof(u32);
+
+  return dst;
+}
+
+static void
+l3vpn_add_ec(const struct f_tree *t, void *P)
+{
+  struct l3vpn_proto *p = P;
+  ec_put(p->export_target_data, p->export_target_length, t->from.val.ec);
+  p->export_target_length += 2;
+}
+
+static void
+l3vpn_prepare_targets(struct l3vpn_proto *p)
+{
+  const struct f_tree *t = p->import_target;
+  p->import_target_one = !t->left && !t->right && (t->from.val.ec == t->to.val.ec);
+
+  uint len = 2 * tree_node_count(p->export_target);
+  p->export_target_data = mb_alloc(p->p.pool, len * sizeof(u32));
+  p->export_target_length = 0;
+  tree_walk(p->export_target, l3vpn_add_ec, p);
+  ASSERT(p->export_target_length == len);
+}
+
+/* Convert 64-bit RD to 32bit source ID, unfortunately it has collisions */
+static inline struct rte_src * l3vpn_get_source(struct l3vpn_proto *p, u64 rd)
+{ return rt_get_source(&p->p, (u32)(rd >> 32) ^ u32_hash(rd)); }
+//{ return p->p.main_source; }
+
+static void
+l3vpn_rt_notify(struct proto *P, struct channel *c0, net *net, rte *new, rte *old UNUSED)
+{
+  struct l3vpn_proto *p = (void *) P;
+  struct rte_src *src = NULL;
+  struct channel *dst = NULL;
+  int export;
+
+  const net_addr *n0 = net->n.addr;
+  net_addr *n = alloca(sizeof(net_addr_vpn6));
+
+  switch (c0->net_type)
+  {
+  case NET_IP4:
+    net_fill_vpn4(n, net4_prefix(n0), net4_pxlen(n0), p->rd);
+    src = p->p.main_source;
+    dst = p->vpn4_channel;
+    export = 1;
+    break;
+
+  case NET_IP6:
+    net_fill_vpn6(n, net6_prefix(n0), net6_pxlen(n0), p->rd);
+    src = p->p.main_source;
+    dst = p->vpn6_channel;
+    export = 1;
+    break;
+
+  case NET_VPN4:
+    net_fill_ip4(n, net4_prefix(n0), net4_pxlen(n0));
+    src = l3vpn_get_source(p, ((const net_addr_vpn4 *) n0)->rd);
+    dst = p->ip4_channel;
+    export = 0;
+    break;
+
+  case NET_VPN6:
+    net_fill_ip6(n, net6_prefix(n0), net6_pxlen(n0));
+    src = l3vpn_get_source(p, ((const net_addr_vpn6 *) n0)->rd);
+    dst = p->ip6_channel;
+    export = 0;
+    break;
+
+  case NET_MPLS:
+    return;
+  }
+
+  if (new)
+  {
+    const rta *a0 = new->attrs;
+    rta *a = alloca(RTA_MAX_SIZE);
+    *a = (rta) {
+      .source = RTS_L3VPN,
+      .scope = SCOPE_UNIVERSE,
+      .dest = a0->dest,
+      .pref = dst->preference,
+      .eattrs = a0->eattrs
+    };
+
+    nexthop_link(a, &a0->nh);
+
+    /* Do not keep original labels, we may assign new ones */
+    ea_unset_attr(&a->eattrs, tmp_linpool, 0, EA_MPLS_LABEL);
+    ea_unset_attr(&a->eattrs, tmp_linpool, 0, EA_MPLS_POLICY);
+
+    /* We are crossing VRF boundary, NEXT_HOP is no longer valid */
+    ea_unset_attr(&a->eattrs, tmp_linpool, 0, EA_BGP_NEXT_HOP);
+    ea_unset_attr(&a->eattrs, tmp_linpool, 0, EA_BGP_MPLS_LABEL_STACK);
+
+    if (export)
+    {
+      struct mpls_channel *mc = (void *) p->p.mpls_channel;
+      ea_set_attr_u32(&a->eattrs, tmp_linpool, EA_MPLS_POLICY, 0, EAF_TYPE_INT, mc->label_policy);
+
+      struct adata *ad = l3vpn_export_targets(p, ea_get_adata(a0->eattrs, EA_BGP_EXT_COMMUNITY));
+      ea_set_attr_ptr(&a->eattrs, tmp_linpool, EA_BGP_EXT_COMMUNITY, 0, EAF_TYPE_EC_SET, ad);
+
+      /* Replace MPLS-incompatible nexthop with lookup in VRF table */
+      if (!mpls_valid_nexthop(a) && p->p.vrf)
+      {
+	a->dest = RTD_UNICAST;
+	a->nh = (struct nexthop) { .iface = p->p.vrf };
+      }
+    }
+
+    /* Keep original IGP metric as a base for L3VPN metric */
+    if (!export)
+      a->igp_metric = a0->igp_metric;
+
+    rte *e = rte_get_temp(a, src);
+    rte_update2(dst, n, e, src);
+  }
+  else
+  {
+    rte_update2(dst, n, NULL, src);
+  }
+}
+
+
+static int
+l3vpn_preexport(struct channel *C, rte *e)
+{
+  struct l3vpn_proto *p = (void *) C->proto;
+  struct proto *pp = e->sender->proto;
+
+  if (pp == C->proto)
+    return -1;	/* Avoid local loops automatically */
+
+  switch (C->net_type)
+  {
+  case NET_IP4:
+  case NET_IP6:
+    return 0;
+
+  case NET_VPN4:
+  case NET_VPN6:
+    return l3vpn_import_targets(p, ea_get_adata(e->attrs->eattrs, EA_BGP_EXT_COMMUNITY)) ? 0 : -1;
+
+  case NET_MPLS:
+    return -1;
+
+  default:
+    bug("invalid type");
+  }
+}
+
+static void
+l3vpn_reload_routes(struct channel *C)
+{
+  struct l3vpn_proto *p = (void *) C->proto;
+
+  /* Route reload on one channel is just refeed on the other */
+  switch (C->net_type)
+  {
+  case NET_IP4:
+    channel_request_feeding(p->vpn4_channel);
+    break;
+
+  case NET_IP6:
+    channel_request_feeding(p->vpn6_channel);
+    break;
+
+  case NET_VPN4:
+    channel_request_feeding(p->ip4_channel);
+    break;
+
+  case NET_VPN6:
+    channel_request_feeding(p->ip6_channel);
+    break;
+
+  case NET_MPLS:
+    /* FIXME */
+    break;
+  }
+}
+
+static inline u32
+l3vpn_metric(rte *e)
+{
+  u32 metric = ea_get_int(e->attrs->eattrs, EA_GEN_IGP_METRIC, e->attrs->igp_metric);
+  return MIN(metric, IGP_METRIC_UNKNOWN);
+}
+
+static int
+l3vpn_rte_better(rte *new, rte *old)
+{
+  /* This is hack, we should have full BGP-style comparison */
+  return l3vpn_metric(new) < l3vpn_metric(old);
+}
+
+static void
+l3vpn_postconfig(struct proto_config *CF)
+{
+  struct l3vpn_config *cf = (void *) CF;
+
+  if (!!proto_cf_find_channel(CF, NET_IP4) != !!proto_cf_find_channel(CF, NET_VPN4))
+    cf_error("For IPv4 L3VPN, both IPv4 and VPNv4 channels must be specified");
+
+  if (!!proto_cf_find_channel(CF, NET_IP6) != !!proto_cf_find_channel(CF, NET_VPN6))
+    cf_error("For IPv6 L3VPN, both IPv6 and VPNv6 channels must be specified");
+
+  if (!proto_cf_find_channel(CF, NET_MPLS))
+    cf_error("MPLS channel not specified");
+
+  if (!cf->rd)
+    cf_error("Route distinguisher not specified");
+
+  if (!cf->import_target && !cf->export_target)
+    cf_error("Route target not specified");
+
+  if (!cf->import_target)
+    cf_error("Import target not specified");
+
+  if (!cf->export_target)
+    cf_error("Export target not specified");
+}
+
+static struct proto *
+l3vpn_init(struct proto_config *CF)
+{
+  struct proto *P = proto_new(CF);
+  struct l3vpn_proto *p = (void *) P;
+  // struct l3vpn_config *cf = (void *) CF;
+
+  proto_configure_channel(P, &p->ip4_channel, proto_cf_find_channel(CF, NET_IP4));
+  proto_configure_channel(P, &p->ip6_channel, proto_cf_find_channel(CF, NET_IP6));
+  proto_configure_channel(P, &p->vpn4_channel, proto_cf_find_channel(CF, NET_VPN4));
+  proto_configure_channel(P, &p->vpn6_channel, proto_cf_find_channel(CF, NET_VPN6));
+  proto_configure_channel(P, &P->mpls_channel, proto_cf_find_channel(CF, NET_MPLS));
+
+  P->rt_notify = l3vpn_rt_notify;
+  P->preexport = l3vpn_preexport;
+  P->reload_routes = l3vpn_reload_routes;
+  P->rte_better = l3vpn_rte_better;
+
+  return P;
+}
+
+static int
+l3vpn_start(struct proto *P)
+{
+  struct l3vpn_proto *p = (void *) P;
+  struct l3vpn_config *cf = (void *) P->cf;
+
+  p->rd = cf->rd;
+  p->import_target = cf->import_target;
+  p->export_target = cf->export_target;
+
+  l3vpn_prepare_targets(p);
+
+  proto_setup_mpls_map(P, RTS_L3VPN, 1);
+
+  if (P->vrf_set)
+    P->mpls_map->vrf_iface = P->vrf;
+
+  return PS_UP;
+}
+
+static int
+l3vpn_shutdown(struct proto *P)
+{
+  // struct l3vpn_proto *p = (void *) P;
+
+  proto_shutdown_mpls_map(P, 1);
+
+  return PS_DOWN;
+}
+
+static int
+l3vpn_reconfigure(struct proto *P, struct proto_config *CF)
+{
+  struct l3vpn_proto *p = (void *) P;
+  struct l3vpn_config *cf = (void *) CF;
+
+  if (!proto_configure_channel(P, &p->ip4_channel, proto_cf_find_channel(CF, NET_IP4)) ||
+      !proto_configure_channel(P, &p->ip6_channel, proto_cf_find_channel(CF, NET_IP6)) ||
+      !proto_configure_channel(P, &p->vpn4_channel, proto_cf_find_channel(CF, NET_VPN4)) ||
+      !proto_configure_channel(P, &p->vpn6_channel, proto_cf_find_channel(CF, NET_VPN6)) ||
+      !proto_configure_channel(P, &P->mpls_channel, proto_cf_find_channel(CF, NET_MPLS)))
+    return 0;
+
+  if ((p->rd != cf->rd) ||
+      !same_tree(p->import_target, cf->import_target) ||
+      !same_tree(p->export_target, cf->export_target))
+    return 0;
+
+  /*
+  if (!same_tree(p->import_target, cf->import_target))
+  {
+    if (p->vpn4_channel && (p->vpn4_channel->channel_state == CS_UP))
+      channel_request_feeding(p->vpn4_channel);
+
+    if (p->vpn6_channel && (p->vpn6_channel->channel_state == CS_UP))
+      channel_request_feeding(p->vpn6_channel);
+  }
+
+  if (!same_tree(p->export_target, cf->export_target))
+  {
+    if (p->ip4_channel && (p->ip4_channel->channel_state == CS_UP))
+      channel_request_feeding(p->ip4_channel);
+
+    if (p->ip6_channel && (p->ip6_channel->channel_state == CS_UP))
+      channel_request_feeding(p->ip6_channel);
+  }
+  */
+
+  proto_setup_mpls_map(P, RTS_L3VPN, 1);
+
+  return 1;
+}
+
+static void
+l3vpn_copy_config(struct proto_config *dest UNUSED, struct proto_config *src UNUSED)
+{
+  /* Just a shallow copy, not many items here */
+}
+
+static void
+l3vpn_get_route_info(rte *rte, byte *buf)
+{
+  u32 metric = l3vpn_metric(rte);
+  if (metric < IGP_METRIC_UNKNOWN)
+    bsprintf(buf, " (%u/%u)", rte->attrs->pref, metric);
+  else
+    bsprintf(buf, " (%u/?)", rte->attrs->pref);
+}
+
+
+struct protocol proto_l3vpn = {
+  .name =		"L3VPN",
+  .template =		"l3vpn%d",
+  .class =		PROTOCOL_L3VPN,
+  .channel_mask =	NB_IP | NB_VPN | NB_MPLS,
+  .proto_size =		sizeof(struct l3vpn_proto),
+  .config_size =	sizeof(struct l3vpn_config),
+  .postconfig =		l3vpn_postconfig,
+  .init =		l3vpn_init,
+  .start =		l3vpn_start,
+  .shutdown =		l3vpn_shutdown,
+  .reconfigure =	l3vpn_reconfigure,
+  .copy_config = 	l3vpn_copy_config,
+  .get_route_info =	l3vpn_get_route_info
+};
+
+void
+l3vpn_build(void)
+{
+  proto_build(&proto_l3vpn);
+}