Two NAT routers on the same subnet?

Network related discussions (including general TCP/IP stuff, routing, etc).

Two NAT routers on the same subnet?

Postby mlager » 18 Feb 2012, 00:20

I have a network, 172.16.3.0/24, that has a NAT router (PF)

Ext: A.A.A.A
Internal: 172.16.3.1

Currently, clients use 172.16.3.1 as their default gateway for the Internet. I want to bring in a second Internet connection and have certain devices obtain the Internet through it. Is it possible to add a second NAT router, such as:

Ext: B.B.B.B
Internal: 172.16.3.2

And then have certain devices on the network use a default gateway of 172.16.3.1 to push trafic through A.A.A.A and other devices on the network use a default gateway of 172.16.3.2 to push traffic through B.B.B.B? Both internal interfaces would be on the same switch.

It seems logical and I can't figure out why that wouldn't work, but I thought I'd check with some experts first.

Thanks for any advice!
mlager
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Postby bbzz » 18 Feb 2012, 02:16

Yes, that's possible, the fact that both gateways are one same LAN doesn't matter.

You could also have one gateway which load balances over two Internet connections.
If you have multiple exit points, look into CARP.
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Postby mlager » 18 Feb 2012, 03:06

Great thanks for the response... Now I've run into something that is pretty annoying. I brought in a U-Verse connection from AT&T (B.B.B.B) and the useless modem / router they included has not ability to disable its DHCP functionality. And I don't want anything grabbing addresses from it because the only point of the AT&T connection is to power the VOIP system. But it hands out addresses and forces itself to be the default gateway.

I'm not on-site, but it seems my only option, at least with this hardware, is to install another network card in the VOIP system, and plug directly into that. The other network card would plug into the existing network. That way the existing network would never query the new AT&T router for addresses and would just get them from the FreeBSD system like they always did.

I guess I could go static IP addresses on clients in the meantime.
mlager
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Joined: 08 Jan 2011, 03:17


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