Commit 1db1b9ba for quagga.net

commit 1db1b9baea511995b67a9b282d5c97e87479fe5d
Author: Mathieu Jadin <mathjadin@gmail.com>
Date:   Thu Dec 14 17:53:53 2017 +0100

    bgpd: Fix mistake in NHT of connected IPv6 next-hops preventing route advertisement

    Since quagga-1.2.0, the Next Hop validation for directly connected peers
    using IPv6 does not work.

    In this setup, BGP updates contain two next hops: a global IPv6 address and
    a link-local IPv6 address (a correct behavior according to RFC 2545).  This
    means that the length of the next hop attribute is 32 and not 16.

    The problem comes from the function "make_prefix()" in "bgpd/bgp_nht.c".  It
    refuses to build a prefix structure for a route when the length of the
    [Anext hop attribute is different from 16, even if a valid global IPv6
    address is available.

    The route is mistakenly considered invalid and thus, it is not installed in
    the routing table.

    Details: "make_prefix()" was not modified in quagga-1.2.0 but its
    interpretation was changed in commit
    3dda6b3eccb9a2a88d607372c83c04c796e7daac.  Before this commit, the failure
    of "make_prefix()" was interpreted as a successful validation of the next
    hop.

diff --git a/bgpd/bgp_nht.c b/bgpd/bgp_nht.c
index 1158ab15..d734c201 100644
--- a/bgpd/bgp_nht.c
+++ b/bgpd/bgp_nht.c
@@ -409,8 +409,8 @@ make_prefix (int afi, struct bgp_info *ri, struct prefix *p)
       break;
 #ifdef HAVE_IPV6
     case AFI_IP6:
-      if (ri->attr->extra->mp_nexthop_len != 16
-	  || IN6_IS_ADDR_LINKLOCAL (&ri->attr->extra->mp_nexthop_global))
+      if (ri->attr->extra->mp_nexthop_len == 16
+	  && IN6_IS_ADDR_LINKLOCAL (&ri->attr->extra->mp_nexthop_global))
 	return -1;

       p->family = AF_INET6;