bgpd: Pass non-transitive ext-communities between Route Server and RS clients

https://datatracker.ietf.org/doc/html/rfc7947#section-2.2

Optional recognized and unrecognized BGP attributes,
   whether transitive or non-transitive, SHOULD NOT be updated by the
   route server (unless enforced by local IXP operator configuration)
   and SHOULD be passed on to other route server clients.

By default LB ext-community works with iBGP peers. When we receive a route
from eBGP peer, we can send LB ext-community to iBGP peers.

With this patch, allow sending LB ext-community to iBGP/eBGP peers if they
are set as RS clients.

FRR does not send non-transitive ext-communities to eBGP peers, but for
example GoBGP sends and if it's set as RS client, we should pass those attributes
towards another RS client.

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>

diff --git a/bgpd/bgp_attr.c b/bgpd/bgp_attr.c
index e1ee0277008ec79f8c3ae4ee72ba39aedde1e74c..df03e9a34d819d05d001f55ad83e7cd790d2b3a1 100644 (file)
--- a/bgpd/bgp_attr.c
+++ b/bgpd/bgp_attr.c
@@ -4177,9 +4177,14 @@ bgp_size_t bgp_packet_attribute(struct bgp *bgp, struct peer *peer,
        if (CHECK_FLAG(peer->af_flags[afi][safi], PEER_FLAG_SEND_EXT_COMMUNITY)
            && (attr->flag & ATTR_FLAG_BIT(BGP_ATTR_EXT_COMMUNITIES))) {
                struct ecommunity *ecomm = bgp_attr_get_ecommunity(attr);
-
-               if (peer->sort == BGP_PEER_IBGP
-                   || peer->sort == BGP_PEER_CONFED) {
+               bool transparent = CHECK_FLAG(peer->af_flags[afi][safi],
+                                             PEER_FLAG_RSERVER_CLIENT) &&
+                                  from &&
+                                  CHECK_FLAG(from->af_flags[afi][safi],
+                                             PEER_FLAG_RSERVER_CLIENT);
+
+               if (peer->sort == BGP_PEER_IBGP ||
+                   peer->sort == BGP_PEER_CONFED || transparent) {
                        if (ecomm->size * 8 > 255) {
                                stream_putc(s,
                                            BGP_ATTR_FLAG_OPTIONAL