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Multihomed NT

By coscollu ·
I have an NT with 3 network cards. When I ping any host in any of the networks, I found that I an using a TCPIP address assigned to one of the network cards. How can I change this address that was assigned to my machine? I would like to use the address of the other nic card.

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Multihomed NT

by NetTek In reply to Multihomed NT

You need to add Route statements to the NT machine to tell it which NIC to use in order to get to each subnet. For example, let's say NIC A's IP address is 10.0.0.123, and it is connected to the network 10.0.0.0. You need to go to a command promptand type the following:
c:\route.exe -p add 10.0.0.0 mask 255.0.0.0 10.0.0.123
The "-p" makes the route persistant, or else it would be deleted after reboot.
"10.0.0.0" is the subnet reached by that NIC.
"mask" is the subnet mask.
10.0.0.123 isthe NIC's IP address.
So basically, that Route statement tells your NT machine that to get to the 10.0.0.0 network with the subnet mask of 255.0.0.0, to use the NIC card with the address 10.0.0.123.
You can repeat this for all of your cards.

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Multihomed NT

by coscollu In reply to Multihomed NT

The route 10.0.0.0 mask 255.0.0.0 gateway 10.0.0.123 interface 10.0.0.123 is automatically added by NT when you assign the address and mask to the nic. I have 3 of those routes present.

The route statement tells the NT in what nic to use for a given address but I do not think it defines what source address will be used by NT.

The answer might be related to the binding sequence but i am not so sure.

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Multihomed NT

by Some Guy in Seattle In reply to Multihomed NT

TCP/IP will naturally resort to using the local subnet for passing traffic if it sees the destination as being on the local subnet. This is default behavior and is part of the design of the protocol.

However, if you are interested in forcing a ping across a different card, use ping -j (loose source route) or ping -k (strict) to force it to use a different source IP and routing (use ping /? to see the different switches available for ping). Note that there must be at least one router between your forced source IP and the destination.

The previous poster was correct in saying you can create new routes. By default, the ones you mentioned are in there but these can be removed and remodified, and others may be added - strange things may occur however since TCP/IP is being forced to run outside of it's design. These routes are also much more difficult to maintain since the logic of TCP/IP communication is being circumvented.

Apologies if this isn't what you wanted to hear, but hope that helps,

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Multihomed NT

by coscollu In reply to Multihomed NT

Thanks.

Here are additional details of my problem

Nic1: 10.0.0.1 mask 255.255.255.0 no gateway
Nic2: 10.1.0.1 mask 255.255.255.0 no gateway
Nic3: 10.2.0.1 mask 255.255.255.0 default gateway 10.2.0.2

Ping 10.0.0.5 Using sniffer source ip 10.1.0.1
Ping 10.1.0.5 Using sniffer source ip 10.1.0.1
Ping 10.2.0.5 Using sniffer source ip 10.1.0.1

I want sniffer source ip to be 10.0.0.1

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Multihomed NT

by Harold In reply to Multihomed NT

Q: where do you apply the sniffer?
I hope you're not sniffing on the 3 nic machine?

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Multihomed NT

by coscollu In reply to Multihomed NT

It is in the machines that I ping. Not on the 3 nic machine.

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