bgpd: replace ipv4-mapped ipv6 at update forwarding

Replace IPv4-mapped IPv6 at update forwarding because the peer may not
be able to create a route with the IPv4-mapped IPv6.

Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>

bgpd/bgp_updgrp_packet.c

@@ -508,6 +508,9 @@ struct stream *bpacket_reformat_for_peer(struct bpacket *pkt,
  gnh_modified = 1;
  }
  } else if (IN6_IS_ADDR_UNSPECIFIED(&v6nhglobal)) {
+ /* the UPDATE is originating from the local router.
+ * Build the global nexthop.
+ */
  mod_v6nhg = &peer->nexthop.v6_global;
  gnh_modified = 1;
  } else if ((peer->sort == BGP_PEER_EBGP)
@@ -521,6 +524,14 @@ struct stream *bpacket_reformat_for_peer(struct bpacket *pkt,
  */
  mod_v6nhg = &peer->nexthop.v6_global;
  gnh_modified = 1;
+ } else if (IS_MAPPED_IPV6(&v6nhglobal) &&
+ !IN6_IS_ADDR_LINKLOCAL(&peer->nexthop.v6_global)) {
+ /* prefer a IPv6 native global address over
+ * an IPv4-mapped IPv6 address as nexthop when
+ * forwarding UPDATEs.
+ */
+ mod_v6nhg = &peer->nexthop.v6_global;
+ gnh_modified = 1;
  }
 
  if (peer->nexthop.v4.s_addr != INADDR_ANY &&
@@ -535,6 +546,10 @@ struct stream *bpacket_reformat_for_peer(struct bpacket *pkt,
  }
 
  if (IS_MAPPED_IPV6(&peer->nexthop.v6_global)) {
+ /* If the interface to the peer has no global IPv6
+ * address, replace the nexthop in UPDATE with
+ * the IPv4-mapped IPv6 address if any.
+ */
  mod_v6nhg = &peer->nexthop.v6_global;
  gnh_modified = 1;
  }