I have an iptables script that works correctly in Ubuntu 10.04, but fails in one crucial respect in Ubuntu 12.04.
Specifically, a rule of this form:
iptables -A PREROUTING -t nat -s 192.168.nnn.0/22 -p tcp -m multiport --dports 80,443 -m mark --mark 0x8/0x8 -j REDIRECT
Does not seem to work in 12.04 but does in 10.04. I have put LOG rules immediately before and after this rule, and the first one of these creates an entry in the log file whereas (as expected) the second doesn't; thereafter the packet seems to disappear! Any suggestions welcomed.