Using NAT, address not being translated in DNS request

[bgottesman]

My Linux host has a 10.* address on a network. My guest is communicating with that network via NAT, and has a 192.* address on the internal network. The DNS server on the external network is seeing the guest's internal 192.* address.

Am I correct in believing that that is not supposed to happen? Isn't the virtual NAT device supposed to translate the guest's 192.* address to the host's 10.* address?

I'm using VMware Player 1.0.3 build-34682. The NAT is configured in the default way as far as I know.

[nick_couchman]

Host O/S? Guest O/S? DNS Server O/S?

[bgottesman]

Host OS: Knoppix 5.0.1

Guest OS: Windows XP

DNS Server OS: Windows 2000

[nick_couchman · Accepted solution]

I'm assuming you're running Dynamic DNS. If so, this is because the guest sends out the DDNS update with its own hostname and IP address. NAT may change the source and destination of the packets, but it doesn't fool with the data in the packets, so the DDNS update done by the client probably still has the original IP address. Besides, that would be a little bit sticky if, using NAT, both your Knoppix host O/S and your XP guest tried to update the DNS server with the same IP for two different hostnames. Only one can win...

[bgottesman]

It is Dynamic DNS, and using Snort on the host I saw a packet going from the host to the DNS server containing the VM's IP address (reversed, actually, i.e. 128.73.168.192) in the payload, so I gather you're right.

So let me ask this follow-up question:

If I want to configure the NAT to allow machines on the external network to initiate communication with the VM, will this be complicated by the fact that DNS sees the VM's internal IP address? As I understand it, the external machines need to send such communcation to the host to be forwarded, in other words they need to think that the host's IP address is the VM's. Is that correct?