Switching from old to new firewall, ISA/TMG; why does it not work (network related)?

Posted on 2011-02-24
Last Modified: 2012-05-11
We have an old ISA server with public IP addresses configured for NIC "Internet" and private IP adress for NIC "LAN", and several firewall rules.

We have implemented a new TMG server with the same IP configuration as the old, and the same firewall rules. It is as far as possible identical.

We switched between them, pulling the TP cables from ISA and shoved them into the TMG.

What happened was, that both LAN and Internet NIC had the status of "Unidentified Network - No internet access", and Windows complained that there was an IP address conflict (on LAN).

I admit that our switch was a bit on the optimistic side, but nonetheless I can't figure out why it doesn't work. Has it something to do with IP address--MAC address mappings in routers and switches, and if so, surely I don't need to restart every node, TMG included?
Question by:Jack_A_Roe
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LVL 24

Accepted Solution

rfc1180 earned 500 total points
ID: 34971438
sounds like stale ARP entries; what is upstream to the ISA?
LVL 51

Expert Comment

by:Keith Alabaster
ID: 34974119
There is more to configuring the FTMG than just the ip addresses and firewall rules. I assume you also set up the local address tables for the internal LAN subnet range? Regardless of whether you have or not, the FTMG config is not going to report on duplicate IP addresses - this is still down at the network layer.


Author Comment

ID: 34978295
rfc1180, there's a switch, and there's the ISP router.
keith, I'm not sure what you mean with "I assume you also set up the local address tables for the internal LAN subnet range?" Would you mind clarify?

I might have misconfigured the default gateway; I'll correct this and get back to you as soon as I have been able to test this.
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Author Comment

ID: 34978687
Forget about the default gateway comment by me.

I did a new test today, and found out that I from the TMG could ping my ISPs router; but the connections are at "Unidentified network - No internet access" nonetheless, and the gateway simply does not work in any direction.

What I'm doing is switching from one firewall (ISA) to another (TMG). Could this switch need some time to update arp tables and such; would that make a big difference? The new server is only online for a couple of minutes...?

Author Comment

ID: 34979318
It struck me as weird that the LAN NIC of the new TMG had the status of "Unidentified network", it being the subnet of my internal Active Directory domain. Never seen that before.

I changed the IP address on LAN NIC of the new TMG from (the LAN NIC address of the old ISA server and the LAN NIC IP address of the new TMG) to, and put the cable back into the LAN switch. After a couple of seconds the connection got the status of "[Your Internal Active Directory Domain]".

But once again, when I changed the IP address on LAN NIC of the new TMG to, and put the cable back into the LAN switch I get "Unidentified network" and a message about IP address conflict (even though the other server is not connected).
LVL 24

Assisted Solution

rfc1180 earned 500 total points
ID: 34981349
Typically switches will age out the cam/mac table when a port goes down. A layer 3's arp table will not age out until after a predetermined time. When you change the ip address routers and hosts wil still have the old MAC address in the arp table.


Author Comment

ID: 34991489
Now I have been able to 1) shut down both servers, detach the old from network, and 2) start the new attached (w. common IP address). Then it works.
LVL 24

Expert Comment

ID: 34992210
You could have also just forced the arp table on the server and hosts to age out arp -d x.x.x.x; something to remember in the future.


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