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Beginner

2-Byte ASN interop with 4-Byte ASN

Hi,

My requirement is to run IBGP between my 2-byte BGP speaker with an router reflector which is  a 4-byte ASN BGP speaker. Can someone let me know how to do this? I could not use local-as feature with IBGP but works fine with EBGP scenarios. Any pointers or config help will be appreciated.

Details:

Route-Reflector

ASN: 3.3 (196611)

Loopback: 10.1.0.81

PE Router

ASN: 65535

Loopback: 10.1.0.4

Thanks,

Madhu

1 ACCEPTED SOLUTION

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Cisco Employee

Re: 2-Byte ASN interop with 4-Byte ASN

OK thanks for the clarification !!

6 REPLIES 6
Cisco Employee

Re: 2-Byte ASN interop with 4-Byte ASN

Hi Madhu,

Basically there is nothing specific that you need to do. 4B ASN support capability will be exchange during session establishement. If the 4B speaker notice its peer doesn't support 4B ASN, it will take care of any translation of 4B ASN to a specific 2B AS 23456.

Here is a good link: http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6554/ps6599/4byte_asnios.pdf

HTH

Laurent.

Beginner

Re: 2-Byte ASN interop with 4-Byte ASN

Hi Laurent,

Yes it worked but the problem is that there is a hide command to ask the new bgp speaker not to negotiate the 4byte capabilities with old bgp speaker as he does not understand the format in open message.

Now EBGP session is coming up fine but I have a core already running a 4b asn and I need to integrate another PE into that core which have only 2b capability. Obviously I cannot establish an IBGP relationship with either RR or any of the PE routers. Do you know any workaround for such situation?


Thanks,

Madhu

Cisco Employee

Re: 2-Byte ASN interop with 4-Byte ASN

Hi Mahdu,

An old BGP speaker will just ignore the 4B capability and will use the AS_TRANS put in the open message as the peer AS so I'm not sure to understand your point that it doesn't understand the open message format.

You're right, you can't do an iBGP session and you will have to create an eBGP one until you are able to upgrade this PE.

HTH

Laurent.

Beginner

Re: 2-Byte ASN interop with 4-Byte ASN

Hi Laurent,

Yes per standard it should ignore but there was a defect due to which we

are not able to bring up the session. It's fixed now.

Thanks,

Madhu

Cisco Employee

Re: 2-Byte ASN interop with 4-Byte ASN

OK thanks for the clarification !!

Beginner

Re: 2-Byte ASN interop with 4-Byte ASN

And thanks for all your help.

Regards,

Madhu

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