igb network lockups

[Christopher D. Harrison]

I recently have been experiencing network "freezes" and network 
"lockups" on our Freebsd 9.1 systems which are running zfs and nfs file 
servers.
I upgraded from 9.0 to 9.1 about 2 months ago and we have been having 
issues with almost bi-monthly.   The issue manifests in the system 
becomes unresponsive to any/all nfs clients.   The system is not 
resource bound as our I/O is low to disk and our network is usually in 
the 20mbit/40mbit range.   We do notice a correlation between temporary 
i/o spikes and network freezes but not enough to send our system in to 
"lockup" mode for the next 5min.   Currently we have 4 igb nics in 2 
aggr's with 8 queue's per nic and our dev.igb reports:

dev.igb.3.%desc: Intel(R) PRO/1000 Network Connection version - 2.3.4

I am almost certain the problem is with the ibg driver as a friend is 
also experiencing the same problem with the same intel igb nic.   He has 
addressed the issue by restarting the network using netif on his 
systems.   According to my friend, once the network interfaces get 
cleared, everything comes back and starts working as expected.

I have noticed an issue with the igb driver and I was looking for 
thoughts on how to help address this problem.
http://freebsd.1045724.n5.nabble.com/em-igb-if-transmit-drbr-and-ALTQ-td5760338.html

Thoughts/Ideas are greatly appreciated!!!

     -C