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ldpd: fix wrong gtsm count

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In linux networking stack, the received mpls packets will be processed
by the host *twice*, one as mpls packet, the other as ip packet, so
its ttl decreased 1.

So, we need release the `IP_MINTTL` value if gtsm is enabled, it is for the
mpls packets of neighbor session caused by the command:
`label local advertise explicit-null`.

This change makes the gtsm mechanism a bit deviation.

Fix PR #8313

Signed-off-by: anlan_cs <vic.lan@pica8.com>
(cherry picked from commit 1919df3a64)
This commit is contained in:
anlan_cs 2024-06-15 20:34:20 +08:00 committed by Mergify
parent fd25804c93
commit 615097b6b0
1 changed files with 12 additions and 0 deletions
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12
ldpd/neighbor.c
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@ -690,6 +690,18 @@ nbr_gtsm_setup(int fd, int af, struct nbr_params *nbrp)
if (nbrp && CHECK_FLAG(nbrp->flags, F_NBRP_GTSM_HOPS))
ttl = 256 - nbrp->gtsm_hops;
/*
* In linux networking stack, the received mpls packets
* will be processed by the host twice, one as mpls packet,
* the other as ip packet, so its ttl will be decreased 1.
* This behavior is based on the new kernel (5.10 and 6.1),
* and older versions may behave differently.
*
* Here, decrease 1 for IP_MINTTL if GTSM is enabled.
* And this workaround makes the GTSM mechanism a bit deviation.
*/
ttl -= 1;
switch (af) {
case AF_INET:
if (sock_set_ipv4_minttl(fd, ttl) == -1)