BGP AS numbers

Answered Question
Aug 12th, 2008
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I have a quick question here would there be a problem if I assign BGP AS number 65145 on a router that already has another AS number? The 65145 I just made up which is perfectly ok right? Sorry someone has always given me a ASN this it the first time I'm making one up.

Correct Answer by lamav about 8 years 8 months ago

You can only run one instance of BGP on any given router.


The private AS number space is 64512 to 65535. So, in terms of selecting an AS, you're fine. In terms of configuring a second BGP AS on the router, you're not fine.


HTH


Victor

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Correct Answer
lamav Tue, 08/12/2008 - 10:14
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You can only run one instance of BGP on any given router.


The private AS number space is 64512 to 65535. So, in terms of selecting an AS, you're fine. In terms of configuring a second BGP AS on the router, you're not fine.


HTH


Victor

Giuseppe Larosa Tue, 08/12/2008 - 10:18
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Hello Warren,

a router can be in only one AS number.

You will get an error if try to enter router bgp 65145.


A router can pretend to be in AS 65145 for a specific BGP neighbor by using the local-as option.


neighbor local-as


To customize the AS_PATH attribute for routes received from an external Border Gateway Protocol (eBGP) neighbor, use the neighbor local-as command in address family or router configuration mode. To disable AS_PATH attribute customization, use the no form of this command.


neighbor {ip-address | peer-group-name} local-as [autonomous-system-number [no-prepend [replace-as [dual-as]]]]


no neighbor {ip-address | peer-group-name} local-as


see

http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_bgp3.html#wp1014448


In your case evaluate if you want to put your router in AS 65145 you first need to remove the current BGP process otherwise use the local-option


Hope to help

Giuseppe


wgranada1 Tue, 08/12/2008 - 11:15
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Is this pretty easy to do? From a quick look at the link you provided it appears so. I'll give it a shot and see how it goes.

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