Question regarding BGP and Exist/Non Exist maps

From: Peter Grewal (peter@avient.ca)
Date: Sat May 31 2008 - 10:02:27 ART


Guys,

 

I just need to make a clarification regarding exist and non exist maps.
Suppose I have two AS, we have router 1 that is in AS 100, and routers 2,3
in AS 200, with R1 connecting to both routers. AS 100 is advertising a
network 1.1.1.0/24, which R1 receives and passes onto R2,R3 as an eBGP
route. Now if I want to only send this router to R3, but in the event R3 is
not available I send it to R2, can an non-exist map be used

 

The reason I ask is that the network is propagated already by AS 100, so if
I use the non-exist map to only advertise network 1.1.1.0/24, when the link
to R3 is down, will this actually prevent the 1.1.1.0/24 network from being
advertised to R2 when the link between R1 and R3 is up ?

 

Thank you.

 

Peter.



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