Fixed a problem on firewall server. The network adapter kept listing the following message in /var/log/messages:

NETDEV WATCHDOG: eth1: transmit timed out
eth1: tx_timeout: tx_done_idx=27 free_idx=18 cmdsts=8000002a

After some searching of Google, I found a solution. You need to load the driver with the option reset_phy=1 and the problem seems to go away.