To acheive some level of network layer redundancy, we would like to have at least two nics that are used to proxy on our s650 (other than the management port). Therefore, it would be logical to just patch another nic into P2 (however I am aware that the Ironport system does not recognise this configuration, as P2 is currently only used as an outbound port for passthrough proxying, I beleive.)
I've just noticed this post on the thread announcing GA of 5.6.0;
To enhance the security of the WSA, we explicitly prevent the WSA from proxying requests on the P2 interface. Customers who need this functionality may want to wait for the 5.6.2 release, which will support this configuration.
So, I take it then that under 5.6.2 (when it is released) I'll be able to set up the dual nic situation as I mentioned above; with both P1 and P2 patched in, so that if one nic / cable / etc dies, it will continue to run merrily on the other port?
Here's hoping ... :)