Comment 5 for bug 1089709

It doesn't make sense to me that I would have to disable a flag to get something more specific to work. If I pass an interface to the floating pool, I expect that to take effect regardless of what I have set in public_interface. It's also confusing that I can specify an interface, the database will show that interface but when I assign the floating IP it doesn't apply it to the interface I want.

Removing the public_interface flag causes the default iptables SNAT rules to watch eth0 which for some installations will be an issue. Specifically, let's say eth0 is my management newtork and eth1 is my default gateway and fixed network interface, I have to have the public_interface flag set to eth1 for instances to be able to reach external networks.

The reason why this hasn't really come up before is that traffic flow and routing will be an issue if you want floating IP traffic to go out a different interface than the default gatway. Very few deployments would ever need to design something different but it does come up. This would be more common for the VLAN manager where you may want to have a floating pool for each vlan.

This may not be a huge problem since Quantum is here but it's come up for a few deployments.