NAT: two guests get same IP address

[quartermain]

Reading the docs I had thought that NAT mode attached all guests to the same NAT router, so that they would be able to talk to each other. However if I set up two Windows Server 2003 guests (hosted either on XP or Ubuntu Gutsy) they get the same IP address of 10.0.2.15, so obviously cannot communicate. So it's like they are both attached to separate router.

Is this intentional?

jim

[frank]

Yes, this is intentional. The guests cannot talk directly with each other over NAT. A network card behind a NAT router is actually invisible. Note that VM B is behind the NAT router from the point of view of VM A.

You have two options to change that: Use the 'internal networking' network interface. Each VM on the same internal network can talk to each other but this traffic is invisible from the outside. Perhaps you setup two network interfaces for your guests, one NAT and one internal network.

Or you use host networking and attach the host network interfaces at the hosts side together with the host NIC. This way, the guests behave like additional PCs on the same net as the host and receive their IP from the same DHCP server as the host.

[quartermain]

I attached a second network adaptor to each VM and used internal networking for that.

I had to switch the host machine from Ubuntu to XP since a) the second network adaptor wasn't recognised by the VMs under the Ubuntu host and b) the reliablility under Ubuntu was not good - frequent aborts.

Pity since Ubuntu only takes 30 mins to set up whereas XP takes most of a day with all the patches etc.