diff options
Diffstat (limited to 'doc/bird.sgml')
| -rw-r--r-- | doc/bird.sgml | 31 |
1 files changed, 20 insertions, 11 deletions
diff --git a/doc/bird.sgml b/doc/bird.sgml index 86f4c507..b35f4944 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. <tag>enable route refresh <m/switch/</tag> 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: <tag>path metric <m/switch/</tag> Enable comparison of path lengths when deciding which BGP route is the best one. Default: on. + <tag>med metric <m/switch/</tag> 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. + <tag>igp metric <m/switch/</tag> Enable comparison of internal distances to boundary routers during best route selection. Default: on. @@ -1233,21 +1242,21 @@ with `<tt/O/') are optional. <descrip> <tag>bgppath <cf/bgp_path/</tag> 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. <tag>int <cf/bgp_local_pref/ [I]</tag> 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. <tag>int <cf/bgp_med/ [O]</tag> 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<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt"> for further discussion of BGP MED attribute. @@ -1281,11 +1290,11 @@ with `<tt/O/') are optional. its own routing policy, it also has a complete freedom about which community attributes it defines and what will their semantics be. - <tag>quad <cf/bgp_originator_id/ [O]</tag> This attribute is created by the + <tag>quad <cf/bgp_originator_id/ [I, O]</tag> 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. - <tag>clist <cf/bgp_cluster_list/ [O]</tag> This attribute contains a list + <tag>clist <cf/bgp_cluster_list/ [I, O]</tag> This attribute contains a list of cluster IDs of route reflectors. Each route reflector prepends its cluster ID when reflecting the route. </descrip> |