change NIC, port forward fails

Netopia Router R9120
Port forwarding works for several devices. when I change the NIC (or
entire machine), the port forwarding for that machine fails.

For example, on Netopia port forward table I have:
       10.1.6.35 701 - 702
This works, until I put new computer in place, then it fails, even
though the ip address of the new machine is the same.

The 'show ip nat trans' command on netopia router shows what looks like
an incoming connection to 10.1.6.23:701, but I get no response from the
computer on 10.1.6.23.

I had a total of 8 devices receiving the port forwards. After replacing
some of them with new machines (but keeping same ip address), now I
have only three that work. These three are still the old machines. I
suspect that if I change them out for new machines, the port forwarding
will fail.

If I add a machine to the port forward list, it will not respond.

Inbound traffic follows this path
  Internet --> netopia router public address --> into a 3com 5500
switch --> out to an unmanages switch --> out to the workstation.

The three working machines are on different subnets and they still
work.

When I put the old machines back on-line, the port forwarding to the ip
address works again.

Only thing I can think of is that there is a table that contains mac
address/ip address relationship (arp?) that is incorrect for the new
NICs on the netopia router or the 5500 switch.

I checked the arp table on the 5500 and the mac/ip address
relationships are correct.

Any ideas?

Thanks
Received on Mon May 1 00:52:22 2006