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Multihoming and routing via WinNT

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by bayk 1 view

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I am new to Win NT and have noted some intereting possibilities by accessing the advanced features relating to the TCP/IP protocol control board.
It seems that the same network card can have several IP adresses and gateways. I've also noted that ona server with more than one network card a routing facility can be set up. I have tried to research both these features on MS' TECHNET to no avail.
Can anyone enlighten me on the uses of these features, how they work, and how do you set them up.
Alternatively can anyone point me in the direction of relevant web based resources.
Thank you.

3 replies

by cm1ll3r

Well I know from experience not alot but some that multihoming NT is quite the TABOO within Microsofts world. Almost to the point where depending on who you get if you call in for support and they find that you are running multihomed that you will be denied support. The problems that you come up agains are browsing and login issues since the machine is multihomed and if you dont massage the routing table the server will not know which interface to respond to traffic out of. Im not sure how NT manages routing across divergent paths and I am guessing that it is a round robin sort of response but not for sure. So if you have a client on network a that sends traffic to the server you could get a response from server nic b thus resulting in a loss of connection. Your client is going to get the response from nic b and not know what to do with it. Sorry this is so broad but like I said .. not much experience with NT and multihoming but when I have its always been a struggle.

Good luck

by addam moody

Looking at the situation in the last post,
where you have a client, and server with 2 NIC's - NIC.A and NIC.B;

The client, which is on the same subnet as NIC.A, sends traffic to the server. There is no danger of the client getting a reply from NIC.B, because NIC.B is on a different subnet to the client. If it's not on a different subnet, then what are you trying to route?

As for how you set it up, all you have to do is specify the IP and subnet mask in the tcp properties for each adapter, then simply check IP forwarding on both cards.
That is, of course, if you're not using DHCP.

I'm not going to go into DHCP config here, but suffice to say i have used an NT machine to 'stand-in' for a hardware router that was on the blink, andi never had a problem getting it going. The most common problem is presented when people try to route from the dialup adapter to the NIC, which is not possible under NT4 w/o 3rd party software.

So basically, because your NIC.A and .B have different IP addresses on the server, then clients on either subnet merely have to make their default gateway the IP address of the server NIC on their subnet. Fairly straightforward, but not when you're doing it for the first time.

Hope this clears it up,

Addam Moody
Support Desk Engineer
MCP,WinNT4 SVR&WKSTN,TCP/IP on WintNT4)
ComputerCORP PTY LTD.

Note: Any ideas and opinions expressed by myself in this post may not directly reflect the opinion of ComputerCORP.

by addam moody

Looking at the situation in the last post,
where you have a client, and server with 2 NIC's - NIC.A and NIC.B;

The client, which is on the same subnet as NIC.A, sends traffic to the server. There is no danger of the client getting a reply from NIC.B, because NIC.B is on a different subnet to the client. If it's not on a different subnet, then what are you trying to route?

As for how you set it up, all you have to do is specify the IP and subnet mask in the tcp properties for each adapter, then simply check IP forwarding on both cards.
That is, of course, if you're not using DHCP.

I'm not going to go into DHCP config here, but suffice to say i have used an NT machine to 'stand-in' for a hardware router that was on the blink, andi never had a problem getting it going. The most common problem is presented when people try to route from the dialup adapter to the NIC, which is not possible under NT4 w/o 3rd party software.

So basically, because your NIC.A and .B have different IP addresses on the server, then clients on either subnet merely have to make their default gateway the IP address of the server NIC on their subnet. Fairly straightforward, but not when you're doing it for the first time.

Hope this clears it up,

Addam Moody
Support Desk Engineer
MCP,WinNT4 SVR&WKSTN,TCP/IP on WintNT4)
ComputerCORP PTY LTD.

Note: Any ideas and opinions expressed by myself in this post may not directly reflect the opinion of ComputerCORP.

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