From 73272f04af40484b72451f541a986da996b0da58 Mon Sep 17 00:00:00 2001 From: Ondrej Zajicek Date: Fri, 22 Apr 2011 16:13:27 +0200 Subject: Adds BGP option related to MED handling. Adds option 'med metric' allows to compare MEDs between routes received from different neighbors. --- doc/bird.sgml | 31 ++++++++++++++++++++----------- 1 file changed, 20 insertions(+), 11 deletions(-) (limited to 'doc') diff --git a/doc/bird.sgml b/doc/bird.sgml index 86f4c50..b35f494 100644 --- a/doc/bird.sgml +++ b/doc/bird.sgml @@ -1121,7 +1121,7 @@ for each neighbor using the following configuration parameters: BIRD does not implement obsoleted RFC 1863, but uses ad-hoc implementation, which behaves like plain EBGP but reduces modifications to advertised route attributes to be transparent (for example does not prepend its AS number to - AS PATH attribute and keep MED attribute). Default: disabled. + AS PATH attribute and keeps MED attribute). Default: disabled. enable route refresh When BGP speaker changes its import filter, it has to re-examine all routes @@ -1205,6 +1205,15 @@ for each neighbor using the following configuration parameters: path metric Enable comparison of path lengths when deciding which BGP route is the best one. Default: on. + med metric Enable comparison of MED + attributes (during best route selection) even between routes + received from different ASes. This may be useful if all MED + attributes contain some consistent metric, perhaps enforced in + import filters of AS boundary routers. If this option is + disabled, MED attributes are compared only if routes are + received from the same AS (which is the standard behavior). + Default: off. + igp metric Enable comparison of internal distances to boundary routers during best route selection. Default: on. @@ -1233,21 +1242,21 @@ with ` bgppath Sequence of AS numbers describing the AS path - the packet will travel through when forwarded according to the particular route. In case of - internal BGP it doesn't contain the number of the local AS. + the packet will travel through when forwarded according to the particular route. + In case of internal BGP it doesn't contain the number of the local AS. int Local preference value used for selection among multiple BGP routes (see the selection rules above). It's used as an additional metric which is propagated through the whole local AS. int The Multiple Exit Discriminator of the route - is an optional attribute which is used on on external (inter-AS) links to + is an optional attribute which is used on external (inter-AS) links to convey to an adjacent AS the optimal entry point into the local AS. - The received attribute may be also propagated over internal BGP links - (and this is default behavior). The attribute value is zeroed when a route - is exported from a routing table to a BGP instance to ensure that the attribute - received from a neighboring AS is not propagated to other neighboring ASes. - A new value might be set in the export filter of a BGP instance. + The received attribute is also propagated over internal BGP links. + The attribute value is zeroed when a route is exported to an external BGP + instance to ensure that the attribute received from a neighboring AS is + not propagated to other neighboring ASes. A new value might be set in + the export filter of an external BGP instance. See RFC 4451 for further discussion of BGP MED attribute. @@ -1281,11 +1290,11 @@ with `quad This attribute is created by the + quad This attribute is created by the route reflector when reflecting the route and contains the router ID of the originator of the route in the local AS. - clist This attribute contains a list + clist This attribute contains a list of cluster IDs of route reflectors. Each route reflector prepends its cluster ID when reflecting the route. -- cgit v1.2.3