[Fedora-xen] NAT Problem

[Jim Klein]

This may not be specifically a xen problem, but I am having an issue with running a xen vm
as a NAT gateway. Basically, the situation is this: Dom0 is set up with 2 bridged ports,
xenbr0 and xenbr1. xenbr0 is on the public network and xenbr1 is on the private
(10.x.x.x). DomU #1 is setup as a router using both interfaces, eth0 public (xenbr0) and
eth1 private (xenbr1) with NAT via iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE.
Now, if I bring up another DomU (#2) on the same box with only 1 interface (eth0) on
xenbr0, it is completely inaccessible by machines routing through DomU #1. However, ssh
into DomU#1, then ssh into DomU#2 from the DomU#1 console works. Further, if I migrate
DomU#2 to another box, it is suddenly accessible to machined routing through DomU#1.
Thanks in advance for any help.