Simple Way for BGP Load Balance and Redundancy?

[davidhvoss]

I have two routers running BGP each connected to a different ISP. One is connected to ISP1 and one is connected to a different ISP2. I have 2 subnets I want to advertise to the Internet and I want to load-balance incoming traffic between these two routers as well as provide backup for one another. I was thinking this would work.

On Router 1 Connected to ISP1

aggregate-address 22.22.0.0 255.255.248.0 summary-only

aggregate-address 23.23.0.0 255.255.248.0

On Router 2 Connected to ISP2

aggregate-address 22.22.0.0 255.255.248.0

aggregate-address 23.23.0.0 255.255.248.0 summary-only

The users on the Internet would prefer the more specific routes for 22.22.0.0 into my Router 2 and prefer the more specific routes for 23.23.0.0 into my Router 1. Therefore I am load-balancing incoming sessions (albeit "subnet load-balancing")

Redundancy:

Should either router fail, the summary address for each subnet is still advertised out on the Internet by the other router and the Internet users will then use that remaining summary address into the other working router if the specific routes are no longer advertised by the failed router.

[alfredshum]

You should also read this:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml

[davidhvoss]

Thanks. I read that document prior to posting. That document states to use AS-PATH prepending which is very unreliable for dictating incoming traffic. Therefore, I made the following suggestion in my post.

If anyone thinks my original post is valid, please let me know. I'd like to stay away from AS-PATH prepending.

Thanks.

[alfredshum]

This is worth to discuss as your configuration is much more simpler and concise. I like it.

I'm not sure how the routes will be summarized at the IXs, but what if the edge routers in each ISP also summarize your routes? If this is true then from the perspective of the IXs, your 2 subnets may appear to have the same prefix length as they are summarized by the ISPs. I'm not sure about the common practice in different ISPs. So will this be possible?