From: "Mark Horn [ Net Ops ]" <mhorn @
Subject: Re: Two ISP's to one DMZ
Date: Mon, 7 Jul 1997 09:51:16 -0400
To: Paul Ferguson <pferguso @
Cc: marc @
de, firewalls @
> Is BGP the only answer? We have several ISP's providing service to us.
> We have our own NIC assigned address block, and a NIC assigned AS number.
> We've been trying (for several months) to set up BGP routing between all
> of our providers. But we've run into trouble.
> One of the providers doesn't want to set up peering with us. Their claim
> is that you can have redundant ISP's through other methods than setting up
> BGP peering. When pressed, they've been conspicuously quiet about what
> these other methods are.
> Is there another way to set up redundancy between two ISP's without doing
> BGP peering?
---------------End of Original Message-----------------
How about this?
________ en1 ______ISP1 with preference of 10
Internal LAN_______ en0 |Firewall|
192.168.X.X | NAT | en2 ______ISP2 with preference of 20
en3 and so on... with preference of X
Each interface has its own preference so if one drops, another is used for
outbound service. For inbound service, each interface is remapped with NAT to
a different IP:
192.168.0.3 <-> 22.214.171.124
192.168.0.4 <-> 126.96.36.199
192.168.0.3 <-> 188.8.131.52
192.168.0.4 <-> 184.108.40.206
192.168.0.3 <-> 220.127.116.11
192.168.0.4 <-> 18.104.22.168
and so on...
If one interface fails or the ISP goes down you just use dynamic-dns to remap
the Domains to a new IP.
www.domain.com was 22.214.171.124, it now is 126.96.36.199
mail.domain.com was 188.8.131.52, it now is 184.108.40.206
If everything is working correctly, you should be able to reach the web server
at 220.127.116.11 or 18.104.22.168 or 22.214.171.124 all at the same time.
I just wanted to expand upon my previous posting as there was some confusion.
We have this working at many customer sites. We also have customers using this
with a back up ISDN link. You can still reach their web and mail servers even
if all their T1s go down.
Michael W. Chalkley Tel: +1.770.772.4567
ZapNet! Inc. Fax: +1.770.475.7640
Suite 400-120 E-mail: mikech @
10945 State Bridge Road mikech @
Alpharetta, GA 30202 http://www.iproute.com