Intel 4-port ethernet adaptor link aggregation issue

[Joe Moog]

We have an iXsystems 1U server (E5) with an Intel 4-port ethernet NIC installed, model I350-T4 (manufactured May of 2013). We're trying to bind the 4 ports on this NIC together into a single lagg port, connected LACP to a distribution switch (Cisco 4900-series). We are able to successfully bind the 2 on-board ethernet ports to a single lagg, however the NIC is not so cooperative. At first we thought we had a bad NIC, but a replacement has not fixed the issue. We are thinking there may be a driver limitation with these Intel ethernet NICs when attempting to bind more than 2 ports to a lagg. 

FreeBSD version:
FreeBSD 9.1-PRERELEASE #0 r244125: Wed Dec 12 11:47:47 CST 2012

rc.conf:
# LINK AGGREGATION
ifconfig_igb2="UP"
ifconfig_igb3="UP"
ifconfig_igb4="UP"
ifconfig_igb5="UP"
cloned_interfaces="lagg0"
ifconfig_lagg0="laggproto lacp laggport igb2 laggport igb3 laggport igb4 laggport igb5"
ifconfig_lagg0="inet 192.168.1.14  netmask 255.255.255.0"

We've confirmed that the lagg module is loaded (clearly, as the pair of on-board ethernet ports can be bound successfully). Binding various combinations of ports on the NIC yields odd results, as sometimes the first one in the list does not negotiate properly, sometimes the last one in the list fails negotiation. Adding interfaces to lagg individually versus all at the same time does not seem to make any difference. At one point we even tried to assign unique and separate IP addresses to the ethernet ports individually, and only a couple of the ports would actually come active and respond to any sort of network activity. Due to this issue with the number of "usable" ports even beyond the link aggregation failure, this is sort of what leads us to believe there may be an issue with the drivers for this card.

We've searched the 'net/lists fairly extensively, and have seen very few instances where people have tried to bind more than 2 ports to a lagg with FreeBSD. Again, 2 ports is no problem, so long as we use the on-board ports; it's the introduction of the Intel NIC and 2 more ports that has us stuck. 

Has anybody had any success with such a setup? 

Joe