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

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 with Multiple ISP's

Is it a must to have "Provider Indipendant IP's" to run BGP with multiple ISP's ? Can I also use private AS number for my installation in this scenario ?

Cisco Employee

Re: BGP with Multiple ISP's

you can use privat AS to receive routing information (if your ISP is ok with it) but you won't be able to advertise your network addresses.

It is not technically required to have provider independent IP.

However, some ISP do not like customers advertising and using ip addresses from other providers.

New Member

Re: BGP with Multiple ISP's


My requirement is follows;

Assume that Cx have two ISP connections, ISP #1 and ISP #2.

Let's assume that we got some traffic from ISP #1. I want the reply ( or return) path for that traffic to take the same backward path ( ie through same ISP #1).

Can we achieve this using private AS sumber ?

Cisco Employee

Re: BGP with Multiple ISP's

I don't see how the private AS number will help you ?

For connection started from the Internet to your network, the only solution I can see, is to configure BGP so that the router check the as-path length to determin the isp to use for the returning traffic (your network to the internet).

This does not guarantee that the traffic will use the same isp for inbound and outbound but the chance is bigger.

For session started from your network to the outside, you could use a different nat pool for each ISP. Like this, traffic will have to come back via the same ISP it went out.


New Member

Re: BGP with Multiple ISP's

The only reason that we are trying to use private AS number is to relief all the burden (including charges) that we have to undergo if we are to use registered AS number.

What I understood from your answer is that it is a must to have registered AS number, for the router to determine entire as-path length.

Am I right ?

Also can I achieve my objective If I am recieveing only the default routes (under BGP) from my ISP ?

( this is just to reduce the burden on the local router )

CreatePlease login to create content