route-map and IPFW fwd

Steve Bertrand iaccounts at
Thu Mar 29 18:21:15 UTC 2007

Hi all,

I think this may be more of a natd question, but I'm not sure.

I'll keep this as short as possible, so if anyone thinks they can help,
just ask for more info if required.

I have a dial-up pool on one interface of a Cisco router, and a DNS
server on a subnet on another int. The DNS server is to be re-ip'd (we
got our own ARIN allocation and need to return our MCI assigned IP's),
so I need to route-map incoming packets from the dun users pointing to
the old DNS server IP, to the new one.

The route-map on the Cisco works. The fwd on the DNS server properly
fwd's the packets sent to the old address to itself on the new address.
The DNS server properly formulates it's response, and the client
receives said response.

The problem is that the DNS server is sending the result back using it's
new IP (which is proper), however, a FreeBSD client will drop the packet
as it states something to the effect "expecting packet from
old.ip.addr.ess, but received from new.ip.addr.ess". I don't know if
Windows will barf, but even if it doesn't, I need a proper solution
until we can manually have our users change the hard coded DNS server info.

Can I force the FreeBSD DNS server to rewrite the src address on the
reply packet to the client so it appears as though it's coming from the
old IP? I've fooled with natd, but just can't get the configuration right.



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