Question : Two Network Cards - One Default Gateway

Hi All,

I am running windows 2003 and my server has two network cards in it. I have configured them both with external ip addresses (they are hooked up to the internet directly).

Nic1 settings:

IP Address: 80.xx.xx.01
Subnet: 255.255.255.128
Gateway: 80.xx.xx.126

Nic2 settings:

IP Address: 80.xx.xx.02
Subnet: 255.255.255.128
Gateway: 80.xx.xx.126

When i set up nic2 i got a warnign message stating "multiple gateways are intended to provide redundancy to a single network. They will not function properly when the gateways are on two seperate disjoined networks.......". As far as i can see, i am not breaking those rules?

The problem is, nic2 does not appear to be working. I can ping it from the server it is installed on, but it is not pingable (or telnettable) from the outside world. Nic1 works fine.

Any ideas?

Answer : Two Network Cards - One Default Gateway

I know exactly what you are trying to do but first let me explain what is going wrong

OK look at this a different way

Look at it from the point of view of a router, not a server

You server will have a routing table just like a router and will obey the rules in that table, the only thing that stops the server from routing traffic between the two cards is that you have told it not to but the principles are the same.

As TWO seperate cards the routing tables will have TWO gateways from the local host NIC1 AND NIC2. Now a router routes traffic between two or more network subnets and sits as a bridge so to say between them - trafic in NIC1, look at the routing table work out where it should go and send it there, either through NIC1 or NIC2 depending upon the rules in the table. YOUR routing table however says that no matter which NIC it comes in it can go out of EITHER gateway and that is just not allowed. routers do not like choice, the like rules and instruction.

Now a router will only need one DEFAULT gateway and that is usually the one nearest the internet or the center of your network. You can have more than one gateway but the default one is always the one at the top of the list. YOUR router (server) has TWO default gateways and they are both the same and it is point ing out the fault.

Explanation why it does this - if the router server was a gateway to the internet you might have two routers attached to it. Your main router and a backup router incase the first one fails. Now the NIC connected to ROUTER1 would have ROUTER1 as the gateway and the NIC connected to ROUTER2 would have ROUTER2 as the gateway BUT the routing table would have ROUTER1 down as the default router and so ALL outbound traffic would come from that gateway. If ROUTER1 failed the next entry in the routing table would be ROUTER2 and so that would be used instead.

IT is THAT rule you have broken.

NOW FOR THE SOLUTION

What you are trying to do is more commonly known as NIC teaming or NIC mirroring and is generally specific to manufacturer. It is generally driver driven - a good example would be to look at Compaq and HP web severs with more than one NIC. You link the two NICs together as a SINGLE NIC and the routing table then sees it as such. If one NIC fails, its, twin will automatically be activated in its place without skipping a heartbeat.  

I am not sure if 2003 server includes this feature as part of the O/S as I have only seen it in proprietry drivers and propriety server setups however it will most likely be found in the properties of the NICs or the software that was bundled with them and manages them if it is in there.

YOUR imediate fix in the event that the two cards will not team/mirror is just to DISABLE the second card. This removes its entries from the routing table and obey the rules of the table.

HOPE THIS HELPS