BGP Multihomed and NAT

[gpedretty]

I have a multihomed network running BGP with 3 separate ISPs on a 3725 router. I have Public Address space (/24 net) that will be used for all internal hosts that need to be reachable from the public internet. But I also have several other internal hosts that do not need to be reached from the public internet, but will still need to connect to the internet and so will be using Private IP address space and thus need to use NAT to connect to the outside. I am trying to figure out what is the best way to do the NAT translation for these private addresses without interferring with the BGP routing of the public addresses. I found a Cisco white paper that discusess this called "Enabling Enterprise Multihoming

with Cisco IOS Network Address

Translation (NAT)" but the examples appear to show it as using separate routers for each ISP, I am doing it all on one router. Is this still the right direction to go and can it all be done on one router?

[vcjones]

Your NAT is independent of your BGP, and can be easily set up to give all your users non-stop access to the Internet. Just set up your NAT so that all the all your ISP links are "outside" while all your users are "inside" and set up NAT as if you had a single ISP connection with a static IP address range (using your public address space). NAT translations are set up independent of the specific interfaces actually used (other than their inside/outside status).

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

[gpedretty]

Your suggestion was the way I was going to do it at first, but it appeared to have the effect of stopping my bgp neighbor communications, and I read on a different cisco document that the NAT translation could affect the unicast packets that the BGP neighbors send out to find each other, is this something I should worry about. I was setting it by using interface overload rather than a nat pool.