Firewall Mode R3000 with NICs in the same subnet stop working after 2.2 patch

This article applies to:

• R3000

Symptoms:

• An R3000 in firewall mode may stop working properly after patching to 2.2 if both NICs are using the same subnet.  This will likely cause an internet outage since the filter is no longer passing packets through itself properly.

Causes:

This problem occurs because in 2.2, the kernel forces the default gateway to route through eth0 - previous versions routed through eth1 instead.  As such, the filter will likely be set to associate its listening/receiving interface with the default gateway.

Resolution:

(1)Modify /etc/sysconfig/network to remove the GATEWAY entry. 
(2)Add the same GATEWAY entry to the file /etc/sysconfig/network-scripts/ifcfg-eth1.
(3)Run ifdown eth1;ifup eth1
(4)Run ifdown eth0;ifup eth0
(5)Run /usr/local/shadow/bin/route_table and compare the route table with before the change to make sure no entries are missing.
(6)Notify the customer not to make GUI changes or click on the save button in network settings, as this will overwrite the fixes.