> The problem that I found was that unless the network interfaces were on different sub-nets
> then lwIP would send the response to the first interface.
> This behaviour may be OK for some applications but in my IEEE15888 application this was a problem.
You're right that lwIP is not designed to work with 2 interfaces in the same subnet (e.g. like in a line topology). But this is a routing problem only. Do other IP stacks support this? Normally, I'd expect that for an IEEE1588 solution, you would need a single interface in lwIP and a 2-port switch instead of a single PHY that does the port selection for you. Instead, you could tell the stack on which interface to send specific packets if you don't need to control this for all packets (although this doesn't allow you to work in a line topology).
Simon