BGP AS path question

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Jul 9th, 2008
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The scenario is we are using some Public AS number such as 30 on our private network. Now, we are connecting to our global netowrk via MPLS. AS number for the MPLS peering is 65123. The AS number that is to be seen in the MPLS cloud and at any other location of the cloud should be only 65123. If I peer the internal routers with the MPLS routers over eBGP, the prefixes advertised from the Internal routers are going to carry AS number 30 in the AS Path throuhout the MPLS cloud, which needs to be avoided.

Is there a way to do that?



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lee.reade Wed, 07/09/2008 - 22:34
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Hi Ramesh,

Are you saying that you have various sites that all have the AS 30 within? and that these sites will now connect to MPLS PE that will use AS 65123?

Are you saying that your problem will be that you will receive routes from PE that have AS 30 in the AS path, therefore they will be dropped by your CE router?

If so then you could use the allow-as in command on the CE to PE connection, this will allow your AS to been seen in the AS path, and kind of bypasses the AS check.

Let me know if I have this correct?



mastram4u Wed, 07/09/2008 - 22:43
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Hi LR,

There is one router with AS 30, peering with another router with AS 31 (customer router) (which are in our private WAN network). The MPLS router with AS 65123(on the CPE,managed by us) will peer with the provider CE(mananged by the provider installed at our premises).

I would like to peer with AS 30 and AS65123,so that the prefix advertised from AS 31 can be advertised to the MPLS cloud.

As per the policy, I should not be leaking the public AS number into the MPLS cloud.

Is there a way to mask As number 30 / 31 to be going out to the MPLS cloud?

n.nandrekar Wed, 07/09/2008 - 22:47
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You can use a policy map to advertise routes to a specific bgp nerighbor and change the AS-PATH for all those routes by matching them with route-map and SET AS-PATH.



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