16.1. State of bridging and iptables
As of Linux 2.4.14, bridging and iptables do not 'see' each other without
help. If you bridge packets from eth0 to eth1, they do not 'pass' by
iptables. This means that you cannot do filtering, or NAT or mangling or
whatever.
There are several projects going on to fix this, the truly right one is by
the author of the Linux 2.4 bridging code, Lennert Buytenhek. He recently
informed us that as of bridge-nf 0.0.2 (see the url above), the code is
stable and usable in production environments. He is now asking the kernel
people if and how the patch can be merged, stay tuned!