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BGP: Fix parsing of MPLS withdrawals

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RFC 3107 was bit vague with regard to labeled withdrawals, RFC 8277
clarified that. The old code was incompatible with some implementations,
namely with Juniper.

Thanks to Vadim Fedorenko for the original patch.
This commit is contained in:
Ondrej Zajicek (work) 2018-07-01 00:43:24 +02:00
parent daf113ac66
commit 93c1defdb0
1 changed files with 4 additions and 3 deletions
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7
proto/bgp/packets.c
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@ -1165,9 +1165,10 @@ bgp_decode_mpls_labels(struct bgp_parse_state *s, byte **pos, uint *len, uint *p
ADVANCE(*pos, *len, 3);
*pxlen -= 24;
/* Withdraw: Magic label stack value 0x800000 according to RFC 3107, section 3, last paragraph */
if (!a && !s->err_withdraw && (lnum == 1) && (label == BGP_MPLS_MAGIC))
break;
/* RFC 8277 2.4 - withdraw does not have variable-size MPLS stack but
fixed-size 24-bit Compatibility field, which MUST be ignored */
if (!a && !s->err_withdraw)
return;
}
while (!(label & BGP_MPLS_BOS));