Commit 3228c72c authored by Ondřej Zajíček's avatar Ondřej Zajíček
Browse files

Implements RFC 5004 - prefer older external routes.

parent 2eece54a
......@@ -981,6 +981,11 @@ for each neighbor using the following configuration parameters:
<tag>path metric <m/switch/</tag> Enable comparison of path lengths
when deciding which BGP route is the best one. Default: on.
<tag>prefer older <m/switch/</tag> Standard route selection algorithm
breaks ties by comparing router IDs. This changes the behavior
to prefer older routes (when both are external and from different
peer). For details, see RFC 5004. Default: off.
<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
Discriminator to be used during route selection when the MED attribute
is missing. Default: 0.
......
......@@ -1044,7 +1044,6 @@ 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))
{
x = ea_find(new->attrs->eattrs, EA_CODE(EAP_BGP, BA_MULTI_EXIT_DISC));
......@@ -1082,12 +1081,19 @@ bgp_rte_better(rte *new, rte *old)
y = ea_find(old->attrs->eattrs, EA_CODE(EAP_BGP, BA_ORIGINATOR_ID));
n = x ? x->u.data : new_bgp->remote_id;
o = y ? y->u.data : old_bgp->remote_id;
/* RFC 5004 - prefer older routes */
/* (if both are external and from different peer) */
if ((new_bgp->cf->prefer_older || old_bgp->cf->prefer_older) &&
!new_bgp->is_internal && n != o)
return 0;
/* rest of RFC 4271 9.1.2.2. f) */
if (n < o)
return 1;
if (n > o)
return 0;
/* RFC 4271 9.1.2.2. g) Compare peer IP adresses */
return (ipa_compare(new_bgp->cf->remote_ip, old_bgp->cf->remote_ip) < 0);
}
......
......@@ -24,6 +24,7 @@ struct bgp_config {
ip_addr source_addr; /* Source address to use */
int next_hop_self; /* Always set next hop to local IP address */
int compare_path_lengths; /* Use path lengths when selecting best route */
int prefer_older; /* Prefer older routes according to RFC 5004 */
u32 default_local_pref; /* Default value for LOCAL_PREF attribute */
u32 default_med; /* Default value for MULTI_EXIT_DISC attribute */
int capabilities; /* Enable capability handshake [RFC3392] */
......
......@@ -22,7 +22,7 @@ CF_KEYWORDS(BGP, LOCAL, NEIGHBOR, AS, HOLD, TIME, CONNECT, RETRY, KEEPALIVE,
BGP_PATH, BGP_LOCAL_PREF, BGP_MED, BGP_ORIGIN, BGP_NEXT_HOP,
BGP_ATOMIC_AGGR, BGP_AGGREGATOR, BGP_COMMUNITY, SOURCE, ADDRESS,
PASSWORD, RR, RS, CLIENT, CLUSTER, ID, AS4, ADVERTISE, IPV4,
CAPABILITIES, LIMIT, PASSIVE)
CAPABILITIES, LIMIT, PASSIVE, PREFER, OLDER)
CF_GRAMMAR
......@@ -65,6 +65,7 @@ bgp_proto:
| bgp_proto MULTIHOP expr VIA ipa ';' { BGP_CFG->multihop = $3; BGP_CFG->multihop_via = $5; }
| bgp_proto NEXT HOP SELF ';' { BGP_CFG->next_hop_self = 1; }
| bgp_proto PATH METRIC bool ';' { BGP_CFG->compare_path_lengths = $4; }
| bgp_proto PREFER OLDER bool ';' { BGP_CFG->prefer_older = $4; }
| bgp_proto DEFAULT BGP_MED expr ';' { BGP_CFG->default_med = $4; }
| bgp_proto DEFAULT BGP_LOCAL_PREF expr ';' { BGP_CFG->default_local_pref = $4; }
| bgp_proto SOURCE ADDRESS ipa ';' { BGP_CFG->source_addr = $4; }
......
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