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Multiple BGP Routes in FIB

  • From: Glen Kent
  • Date: Thu Sep 07 12:50:06 2006
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Hi,

There is an interesting discussion going on in the IDR WG and i am
cross posting a mail on Nanog to hear from the operators, if what is
described below, a common practise followed by them:

>> I don't think its correct to advertise one while using both for
>> forwarding.
>> NOTE: I am assuming that the routes share the same path length but have
>> different AS Paths (as mentioned by you earlier in this mail)
>
> I think this is being done by many providers.

Consider two paths for nlri X

as_path 1 {x y z} next_hop n1
as_path 2 {m n z} next_hop n2

Are you suggesting that providers are installing ecmp routes for X with
next-hops n1 and n2, while advertising only one of the paths to their IBGP
peers?

Yes.
Do providers really do this? Would they install multiple BGP Paths
with different AS Paths (but same length) in their FIB, and yet
advertise only one?

Is the the right thing to do?

Glen




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