bgpd: fix use real SID in BGP nexthop tracking

When receiving an SRv6 BGP update, the nexthop tracking is used
to find out the reachability of the BGP update.

> # show bgp ipv6 vpn fd00:200::/64
> Paths: (1 available, best #1)
> [..]
>     4:4::4:4 from 4:4::4:4 (4.4.4.4)
>       Origin incomplete, metric 0, localpref 100, valid, internal, best (First path received)
>       Extended Community: RT:52:100
>       Remote label: 16
>       Remote SID: 2001:db8:f4::
>       Last update: Mon Mar 11 11:50:04 2024

The IPv6 address used is the "Remote SID". Actually, this value is
incomplete. Remote SID stands for the attribute value received in BGP,
while the label value determines a complement of SRv6 SID value. The
transposition technique authorises that in BGP, and in the above case,
the incoming BGP update has used the transposition length.

When there is a transposition in the SID attribute available, use the
real SID address. The nexthop tracking will use that forged address.

> # show bgp nexthop
> Current BGP nexthop cache:
>  4:4::4:4 valid [IGP metric 30], #paths 0, peer 4:4::4:4
>   gate fe80::dced:1ff:fed6:878c, if ntfp3
>   Last update: Mon Mar 11 11:50:02 2024
>  2001:db8:f4:1:: valid [IGP metric 0], #paths 2
>   gate fe80::dced:1ff:fed6:878c, if ntfp3

Fixes: 26c747ed6c0b ("bgpd: extend make_prefix to form srv6-based prefix")

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>

0 files changed, 0 insertions, 0 deletions