I've developed an lwip client on a microcontroller that does seem to successfully acquire an IP address whenever it is powered up. Also, the device is successfully responding to network-based queries (e.g. socket-based commands, web page "GETs").
The problem I'm having is when I look at the router's "Active IP Table" the device is not present and I'm beginning to wonder if I've done something wrong in the lwip startup procedures.
Does anyone know where I should begin to troubleshoot this?
UPDATE (10/20/2011):
I'm becoming convinced that the device's MAC address is at least somewhat responsible. I discovered conflicting MAC addresses for the target when comparing my Windows ARP table and the MAC address I believed I was setting in the lwip initializations.
The solution to my problem was associated with multiple MAC addresses (5 unique addresses) being used throughout the codebase.