Skip to content

Commit

Permalink
bgpd: fix use real SID in BGP nexthop tracking
Browse files Browse the repository at this point in the history
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: 26c747e ("bgpd: extend make_prefix to form srv6-based prefix")

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>
  • Loading branch information
pguibert6WIND committed Nov 28, 2024
1 parent 855873a commit 8b3b152
Showing 1 changed file with 9 additions and 2 deletions.
11 changes: 9 additions & 2 deletions bgpd/bgp_nht.c
Original file line number Diff line number Diff line change
Expand Up @@ -1066,9 +1066,16 @@ static int make_prefix(int afi, struct bgp_path_info *pi, struct prefix *p)
case AFI_IP6:
p->family = AF_INET6;
if (pi->attr->srv6_l3vpn) {
IPV6_ADDR_COPY(&(p->u.prefix6),
&(pi->attr->srv6_l3vpn->sid));
p->prefixlen = IPV6_MAX_BITLEN;
if (pi->attr->srv6_l3vpn->transposition_len != 0 &&
BGP_PATH_INFO_NUM_LABELS(pi)) {
IPV6_ADDR_COPY(&p->u.prefix6, &pi->attr->srv6_l3vpn->sid);
transpose_sid(&p->u.prefix6,
decode_label(&pi->extra->labels->label[0]),
pi->attr->srv6_l3vpn->transposition_offset,
pi->attr->srv6_l3vpn->transposition_len);
} else
IPV6_ADDR_COPY(&(p->u.prefix6), &(pi->attr->srv6_l3vpn->sid));
} else if (is_bgp_static) {
p->u.prefix6 = p_orig->u.prefix6;
p->prefixlen = p_orig->prefixlen;
Expand Down

0 comments on commit 8b3b152

Please sign in to comment.