BIRD: route selection question

Mikhail A. Grishin magr at ripn.net
Mon Mar 28 13:25:51 CEST 2011


Hi, Ondrej

Thank you for explanation.

One more question: is it possible to add "bgp always-compare-med" option 
in BIRD?


Ondrej Zajicek wrote, 28.03.2011 15:31:
> On Mon, Mar 28, 2011 at 01:46:50PM +0400, Mikhail A. Grishin wrote:
>> Hi,
>>
>> Why in the example below, the route via 194.226.100.51 is the best?
>>
>> According http://bird.network.cz/?get_doc&f=bird-6.html#ss6.1
>> Route selection rules
>> ...
>> "Prefer the lowest value of the Multiple Exit Discriminator."
> 
> As specified by BGP standard, MED is used to compare routes only if they
> came from the same neighboring AS [*]. These came from a different ones
> (20632 and 3277), so MED is not used and they are probably compared
> by router ID, time of route or similar low-priority criteria.
> 
> 
> [*] Perhaps it is not explicitly mentioned in documentation, but it is a
> standard BGP behavior.
> 




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