I'm trying to replicate on a small Linux-based router a behavior I've seen elsewhere, such as in cable modems: I need to get a single DHCP address from the WAN side, offer/pass that same address to the single attached client device, and mostly just act as a bridge, except that I also need to have the router use that DHCP-issued address to phone home for management. Also, the client device should be able to talk to the router using some fixed IP (like 192.168.100.1) for local troubleshooting. Any traffic coming from the outside which isn't a response to a request from the router itself should go straight through to the client device, except maybe for one reserved management port.
The client device phones its own home for management, and tells what IP it got, so it can get called back; otherwise I'd just use NAT and be done.
I'm pretty sure I can do most of this with ebtables/tproxy, but I haven't figured out the proper incantations yet. The WAN side has a single hardware-linked reserved DHCP address, which I can't do anything about. My Plan B is straight bridging (with MAC fix-up) but I'd lose too much management functionality that way.
Can anyone please point me at a full working example I can start from?
