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| -rw-r--r-- | doc/bird.sgml | 15 |
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diff --git a/doc/bird.sgml b/doc/bird.sgml index 7f53f028..b8dabf47 100644 --- a/doc/bird.sgml +++ b/doc/bird.sgml @@ -1316,6 +1316,21 @@ for each neighbor using the following configuration parameters: received from the same AS (which is the standard behavior). Default: off. + <tag>deterministic med <m/switch/</tag> BGP route selection + algorithm is often viewed as a comparison between individual + routes (e.g. if a new route appears and is better than the + current best one, it is chosen as the new best one). But the + proper route selection, as specified by RFC 4271, cannot be + fully implemented in that way. The problem is mainly in + handling the MED attribute. BIRD, by default, uses an + simplification based on individual route comparison, which in + some cases may lead to temporally dependent behavior (i.e. the + selection is dependent on the order in which routes appeared). + This option enables a different (and slower) algorithm + implementing proper RFC 4271 route selection, which is + deterministic. Alternative way how to get deterministic + behavior is to use <cf/med metric/ option. Default: off. + <tag>igp metric <m/switch/</tag> Enable comparison of internal distances to boundary routers during best route selection. Default: on. |