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New Member

BGP question?

My company is looking to peer to two different ISPs, currently we have a private BGP AS number, Can we keep our private AS number of we have to order a public AS number in order to peer to two different ISP's?

5 REPLIES
Purple

Re: BGP question?

Hi,

You will need to get a public AS# if you are going to be peering with two different ISPs.

There are workarounds where you can use private AS numbers but these are not recommended.

Pls remember to rate posts.

Paresh

New Member

Re: BGP question?

Thanks for your response, do you know what are thoses workarounds?

Purple

Re: BGP question?

As I said, this option is fraught with problems but here it is anyway.

Firstly, there is very little chance that both your ISPs will let you use the same private AS#. If they do, your problem is solved because you can announce your routes via BGP to both the ISPs and get them to strip the private AS when they send the routes out to their upstream providers.

The more likely scenario is that you will need to use a different private AS# to peer with each ISP. That creates complications because all of the routers in your AS need to use the same AS# (you can't create more than one BGP process in a cisco router). So what you can do is to configure all your routers to use the private AS# assigned by one of the ISPs. Then, on the peering session with the second ISP, you can use the 'neighbor local-as' command so that your BGP packets use the private AS# assigned by that ISP. There is a link that describes that feature here:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a00800b5d60.html

Pls do rate the posts to show your appreciation for people who take the time to help you solve your issues.

Paresh

New Member

Re: BGP question?

Thank you for your response.. Let assume that both ISP's agreed that I use my private AS number, can I just peer with both of them without even using the local-as number. What could happen if I do that, will that create any technical problems?

Purple

Re: BGP question?

The chances that both ISPs will let you use the same AS# is very, very remote. There is a good possibility that the private AS# you are using with ISP1 has already been assigned by ISP2 to another customer.

But if we assume for a minute that they do, then you certainly do not need to use the local-as option.

However, be prepared for the possibility that you do have to use it...

Pls do remember to rate the posts..

Paresh

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