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BGP Question (Numbers of ASs)

Lets say you have ISP1 and ISP2. These are two different ISPs not redundant connections to the same ISP.

If you're wanting to run BGP, would you get one AS or two AS.

How would that work?

6 REPLIES
Silver

BGP Question (Numbers of ASs)

You would still have just the one AS, and then manipulate the metrics so tha tyou use the one that you want. take a look at:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a008009456d.shtml as well

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Posted by WebUser Steve Rodriguez from Cisco Support Community App

Silver

BGP Question (Numbers of ASs)

I think both ISPs will try to assign you differnt AS numbers from Private numbers. If you want to use to ISPs use this command under BGP configurations:

neighbor x.x.x.x remove-private-as

instead of

neighbor x.x.x.x remote-as 65xxx

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Posted by WebUser Neeraj Jagga from Cisco Support Community App

Silver

BGP Question (Numbers of ASs)

We featured your question on our Facebook page. Check out some of the responses here. http://www.facebook.com/CiscoSupportCommunity/posts/206129799495792

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Posted by WebUser Cisco NetPro from Cisco Support Community App

BGP Question (Numbers of ASs)

That's what I was wondering about Web User. If we're using two different ISPs, I would have a feeling they would assign us different Ass.

Interesting, I've actually never understood neighbor x.x.x.x remove-private-as. I'll check the link out when I get home Web User.

I would assume if we have two different ISPs, but had only one AS which included both network ranges (Is that even possible? we wouldn't have to worry about a transit AS?

Silver

BGP Question (Numbers of ASs)

John, you will most probably get 2 AS numbers from 2 different providers, by configuring remove-remote-as for each neighbor, you will removes the private AS numbers from outgoing eBGP updates. when you look at BGP table after running the command, in the path coulmn, it will not display AS numbers. you are basically dropping AS numbers in outgoing BGP updates. This works in case of eBGP.

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Posted by WebUser Neeraj Jagga from Cisco Support Community App

BGP Question (Numbers of ASs)

Hi John,

It depends. If you use the ISP and you advertise your subnets to the internet you need a public AS.

If you use the SP in order to provide you e.g. a VPN service then you can use a private AS numbers.

The  neighbor x.x.x.x remove-private-as is used only to remove Private AS from the AS path.

In the case that you need to have one different AS for each AS you can achieve this by using the  BGP Local-AS Feature.

The local-AS feature allows a router to appear to be a member of a second autonomous system (AS), in addition to its real AS. This feature can only be used for true eBGP peers.

neighbor x.x.x.x local-as Y

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800949cd.shtml

Hope that helps!

Vasilis

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