bird/proto/l3vpn/l3vpn.c

/*
 *	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:
 * - 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 inline void
l3vpn_prepare_import_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);
}

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_export_targets(struct l3vpn_proto *p)
{
  if (p->export_target_data)
    mb_free(p->export_target_data);

  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);
}

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 = rt_get_source(&p->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 = rt_get_source(&p->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:
    channel_request_feeding(p->ip4_channel);
    channel_request_feeding(p->ip6_channel);
    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;
  p->export_target_data = NULL;

  l3vpn_prepare_import_targets(p);
  l3vpn_prepare_export_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)
    return 0;

  int import_changed = !same_tree(p->import_target, cf->import_target);
  int export_changed = !same_tree(p->export_target, cf->export_target);

  /* Update pointers to config structures */
  p->import_target = cf->import_target;
  p->export_target = cf->export_target;

  proto_setup_mpls_map(P, RTS_L3VPN, 1);

  if (import_changed)
  {
    TRACE(D_EVENTS, "Import target changed");

    l3vpn_prepare_import_targets(p);

    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 (export_changed)
  {
    TRACE(D_EVENTS, "Export target changed");

    l3vpn_prepare_export_targets(p);

    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);
  }

  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);
}