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One server, 2 NICs, 2 default gateways

Posted on 2010-03-24
Medium Priority
Last Modified: 2012-05-09
I have looked through the other posting about multiple default gateways but I am not seeing what I am looking for.

I have a Windows 2003 server that has two NIC cards.  One NIC is connected to our internal network.  The other is connected to our DMZ.  Each of them have their own default gateway.

This server is our FTP and other web services server.  It will work fine for a while and then internal and external users cannot connect to the server.  I have to disable and enable both interfaces for the problem to clear itself.

There have been posts regard the Routing and Remote Access service.  This looks to be the answer but I still don't understand how to configure RRAS to fix the problem I am having.

There are 500 points to the person who can help me get this issue resolved.

Thank you very much,
Question by:csg_int_it

Expert Comment

by:Jeff Morlen
ID: 28476874
Is there a reason you are doing port forwarding on your firewall instead of a DMZ?

Most likely, you are running into a routing loop between your Internal network and your DMZ.
This can corrupt/poison the routing table in Windows server.

I would suggest using port forwarding with your firewall and do away with your DMZ.
By putting your server in the DMZ as well as the internal network, you are circumventing the security that your firewall has.

Author Comment

ID: 28477124
Is port forwarding the same as NATing?

LVL 20

Accepted Solution

edster9999 earned 2000 total points
ID: 28477208
You can set a default gateway on two nics... but you should not really be able to do this.
The definition of a default gateway is the routing off your subnetwork if all else fails.
Two have two of these is a bit pointless.
Really the OSs should ban the idea of having 2 live default gateways.

A better system would be to add extra routes.
If you had a machine with something like this :

192.168.1.x ------- pc ------- 192.168.2.x -------- 192.168.3.x

Ie the machine has two network off it. 192.168.1.x and 192.168.2.x
and a machine or a route bridges off to another network 192.168.3.x (off say and not shown here the internet gateway is on

The the routes should be subnet -> eth 2 subnet -> eth 1 subnet -> eth 2 -> gateway
default -> eth1 -> gateway

LVL 20

Expert Comment

ID: 28477462
>>> Is port forwarding the same as NATing?


Nat = Network address translation.  Mapping a full network like an internal 192.168.1.x network onto one IP address (maybe your public IP)

Port forwarding = when traffic comes in on a port on this public address (like port 80) then forward it to the right box on the inside.  So if you had a web server on then you would port forward all port 80 traffic to that box.

Expert Comment

ID: 28479863
When you setup a default gateway on internal and external it will warn you that having such a setup will "not function properly"...

Set the default gateway on the DMZ interface and leave it blank on the internal and you will be all set.

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