Transit SP does not support 32bit ASN

Unanswered Question
Apr 19th, 2010

Hi,

I work for an ISP and am coordinating with another local ISP to multihome a common customer, we got him a 32 ASN but neither of us support 32 bit ASN yet. We have a common upstream provider who does not support it neither. We decided to use AS23456 on our configuration , should we expect routing issues ? Especially when our provider want to route back the customer traffic ?

Any one can help ?

Regards,

Ghino

I have this problem too.
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Laurent Aubert Wed, 04/21/2010 - 08:36

Hi Ghino,

Correct. If you need to peer with a neighbor belonging to a 4B ASN, you need to use the AS_TRANS (23456) as its remote AS.

4B ASN capability is negociated during the session establishment so the customer router will see none of its neighbors support it so it will use new optional transitive attributes to send the information in addition to the classic AS_PATH which will contain 23456.

- AS4_PATH

- AS4_AGGREGATOR

This link may help: http://www.cisco.com/en/US/partner/prod/collateral/iosswrel/ps6537/ps6554/ps6599/white_paper_C11_516823.html

From routing perspective on your side, it doesn't change anything as it's still a dual-homed customer regardless its AS number. The important thing is you see the same AS number from both peering.

HTH

Laurent.

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