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authorOndrej Zajicek <santiago@crfreenet.org>2009-11-17 11:41:29 +0100
committerOndrej Zajicek <santiago@crfreenet.org>2009-11-17 11:41:29 +0100
commit3228c72cc030f409914134440a7e55bbcfc9ff6a (patch)
tree19a1ee75446e86e620dc0322e5e50e3c4a4eba27
parent2eece54a04d95f534b935ccac4c3959b25516bd5 (diff)
downloadbird-3228c72cc030f409914134440a7e55bbcfc9ff6a.tar
bird-3228c72cc030f409914134440a7e55bbcfc9ff6a.zip
Implements RFC 5004 - prefer older external routes.
-rw-r--r--doc/bird.sgml5
-rw-r--r--proto/bgp/attrs.c10
-rw-r--r--proto/bgp/bgp.h1
-rw-r--r--proto/bgp/config.Y3
4 files changed, 16 insertions, 3 deletions
diff --git a/doc/bird.sgml b/doc/bird.sgml
index 0c2b8fb..40793ed 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -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.
diff --git a/proto/bgp/attrs.c b/proto/bgp/attrs.c
index d839ed0..9c7bc30 100644
--- a/proto/bgp/attrs.c
+++ b/proto/bgp/attrs.c
@@ -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);
}
diff --git a/proto/bgp/bgp.h b/proto/bgp/bgp.h
index 0a82be2..c487aaf 100644
--- a/proto/bgp/bgp.h
+++ b/proto/bgp/bgp.h
@@ -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] */
diff --git a/proto/bgp/config.Y b/proto/bgp/config.Y
index 7360820..9401175 100644
--- a/proto/bgp/config.Y
+++ b/proto/bgp/config.Y
@@ -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; }