diff options
Diffstat (limited to 'proto/bgp/attrs.c')
| -rw-r--r-- | proto/bgp/attrs.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/proto/bgp/attrs.c b/proto/bgp/attrs.c index e1a3671a..95eee9aa 100644 --- a/proto/bgp/attrs.c +++ b/proto/bgp/attrs.c @@ -1118,7 +1118,17 @@ bgp_rte_better(rte *new, rte *old) return 0; /* RFC 4271 9.1.2.2. c) Compare MED's */ - if (bgp_get_neighbor(new) == bgp_get_neighbor(old)) + /* This is noncompliant. Proper RFC 4271 path selection cannot be + * interpreted as finding the best path in some ordering. + * Therefore, it cannot be implemented in BIRD without some ugly + * hacks. This is just an approximation, which in specific + * situations may lead to persistent routing loops, because it is + * nondeterministic - it depends on the order in which routes + * appeared. But it is also the same behavior as used by default in + * Cisco routers, so it is probably not a big issue. + */ + if (new_bgp->cf->med_metric || old_bgp->cf->med_metric || + (bgp_get_neighbor(new) == bgp_get_neighbor(old))) { x = ea_find(new->attrs->eattrs, EA_CODE(EAP_BGP, BA_MULTI_EXIT_DISC)); y = ea_find(old->attrs->eattrs, EA_CODE(EAP_BGP, BA_MULTI_EXIT_DISC)); |