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Diffstat (limited to 'doc/bird.sgml')
| -rw-r--r-- | doc/bird.sgml | 16 |
1 files changed, 11 insertions, 5 deletions
diff --git a/doc/bird.sgml b/doc/bird.sgml index 5ee9562..8fa55f8 100644 --- a/doc/bird.sgml +++ b/doc/bird.sgml @@ -784,7 +784,7 @@ for each neighbor using the following configuration parameters: <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: infinite. + is missing. Default: 0. <tag>default bgp_local_pref <m/number/</tag> Value of the Local Preference to be used during route selection when the Local Preference attribute @@ -806,10 +806,16 @@ with `<tt/O/') are optional. 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/ [IO]</tag> The Multiple Exit Discriminator of the route - is an optional attribute which is often used within the local AS to - reflect interior distances to various boundary routers. See the route selection - rules above for exact semantics. + <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 + 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. + See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt"> + for further discussion of BGP MED attribute. <tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/ if the route has originated in an interior routing protocol or |