Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

BGP and multiple AS and ISPs

My company has multiple IT groups, AS # and ISP's. Yes, the age of mergers and acquisitions. For simplicity, Company A advertises it's publicy routed network through AS# 1 and ISP X. Company B advertises it's publicly routed networks through AS# 2 and ISP y. Company A now wants to share company B's internet pipe while still retaining it's own AS# and publicly routed server, in essence, using company B as a transit. The question is, will this be possible? Many ISP's only allow only contractual AS# to traverse it's network. Will company B's ISP allow company A's AS# to pass through its network? Would it be easier to eliminate Company A's AS# and migrate any DMZ server to Company B's network?

2 REPLIES
Purple

Re: BGP and multiple AS and ISPs

Hi,

There's a nifty little feature that is designed exactly for the circumstances you described here. It allows the use of a local AS# that is different to that expected by the ISP. Here's a document with more details:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122sb/newft/122sbc27/fsbgpdas.pdf

Paresh

PS> Pls do remember to rate posts

Silver

Re: BGP and multiple AS and ISPs

What I think if co. A want to share co. B Internet link, the routes from A will be learned by B then advertise to the ISP Y. You have to configure the B to advertise A's routes but not A's AS#.

You can check the AS-Override to override the AS# of A when advertise from B to ISP Y.

For the ISP side, you have to check w/ the ISP will they allow to advertise transit AS#.

Hope this helps.

131
Views
0
Helpful
2
Replies
CreatePlease login to create content