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Implements deterministic MED handling.

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Thanks to Alexander V. Chernikov for many suggestions.
This commit is contained in:
Ondrej Zajicek
2011-12-22 13:20:29 +01:00
parent cf7f064531
commit be4cd99a36
9 changed files with 245 additions and 27 deletions
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doc/bird.sgml
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@@ -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.