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Cisco BGP 4-Byte ASN compatibility with 2-Byte ASN

Hello Experts,

Can someone please provide me with sample documentation links how how to configure a Cisco router to be compatible with the new 4 Byte AS?

Basically, I would like to setup a lab showing how to make a 2 byte ASN work with a 4 Byte AS?

Additionally, would is needed configure a router for a 4 Byte AS with a sample configuration.


1 Solution
Pretty much the same configuration but the questions is does your software support it?

so, if you enter router bgp ?  What range of ASNs are available? the older 2 byte (16 bIT) filed provided 65535 possibilities, the 4 byte is  32 BIT FIELD, so many more potenetial ASNs.

The problem comes in when legacy BGP software using the 2 byte field peers with a newer bgp software version, or vice versa.

Here is a good link explaining whats going on:


harbor235 ;}
cpatte7372Author Commented:

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