BGP and AS-Override.

Unanswered Question
Jun 30th, 2009
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I have a scenario as described in the attachment.

I have link 1 active and link 2 is configured to have lower LP to ISP1 and ISP2 so that link1

is preferred.

My question is on the PE routers on the Coperate Cloud, it is managed by a third party vendor and

they are planning to use the command 'as-override' on the peering to the routers in R1 and R2 respectively. Therefore I am worried that

since they are using this command 'as-override', would a loop occur via ?

R1 - PE Router 1 - PE Router 2 - R2 or

R2 - PE Router 2 - PE Router 1 - R1

From my understanding, the 'as-overried' command is used on the peering router to override ip subnets with that of the PE router and my worry is that since both the PE routers would be peering in the ASN, a loop 'might' occur this way.

Would this happen ?

Pls advice,


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Collin Clark Tue, 06/30/2009 - 05:10
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At the PE-CE edge all local AS Numbers are removed from the AS-PATH. This prevents the CE router from seeing all but the provider AS number, thus eliminating the need for each site requiring a different AS number. Pretty standard practice.

Hope that helps


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