OK, no-one answered this but I figured it out (isn't it always the same!), so I thought I'd reply in case any finds it useful It was nothing to do with physdev. I installed the iptables 1.2.9 and appararently it needs to be compiled with the 2.6 kernel for nat to work. A bit odd but there you go... On Thu, 4 Dec 2003, Andy Loukes wrote: > I'm using iptables 1.2.9 and kernel 2.6.0-test11.. > > I may be doing something really stupid but if I do this: > iptables -t nat -A POSTROUTING -m physdev --physdev-out eth1 -j SNAT --to-source x.x.x.x > > I get: > iptables: Invalid argument > > but if I just use ACCEPT as the target it works fine, although doesn't do what I want.. > > I've got the bridging an physdev options turned on (otherwise I couldn't use the ACCEPT target).. > > Is this a bug, or am I misunderstanding something? > > -- Andy Loukes http://www.navaho.co.uk Complete Appliance Technology