two Locations , same BGP AS number

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May 15th, 2009
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We have two locations with same AS number which they're connected to two different uplinks (one at Europe and another one at US) when we advertise local IP blocks at Europe location we can't see them at US location and vice versa so we have to use static route to solve this issue to uplink. is there any better solution for this issue?

Any advice would be appreciate.



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Giuseppe Larosa Fri, 05/15/2009 - 12:42
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Hello Mehrdad,

this happens because a BGP speaker doesn't accept a prefix with an AS path attribute that already contains its own AS number.

There is a command that allows to override this behaviour:

neigh x.x.x.x allowas-in n

default n=1

Ideally you should connect the two connections with an EoMPLS service so that you can build an iBGP session.

This can be the best solution on the long term.

On the short term you can use that command on the eBGP session(s) with the upstream providers in the two locations:


if you make use of AS path prepending on backup paths to be able to communicate in case of fault you need to specify a value that includes prepending

neigh x.x.x.x allowas-in n

default value if not specified is 1

Hope to help


ANAND VALMIKI Fri, 05/22/2009 - 13:35
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Use the 'neighbor a.b.c.d allowas-in' command on both routers.


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