Hello,
I'm trying to resolve an issue with regards to PPP and ARP requests. My network topology is as follows,
Laptop (192.168.1.3, ethernet) <-> MCU #1 (192.168.1.4, ethernet) <-> MCU #1 (192.168.1.126, PPP serial [server]) <-> MCU #2 (192.168.1.127 PPP serial [client])
The issue I'm running into is that when I try to send a packet to MCU #2 (192.168.1.127) from the laptop, the ARP request the laptop sends is never satisfied. This makes sense to me, as the instance of lwip running on MCU #1 can't respond to this ARP request as it doesn't have MCU #2's IPÂ address in its routing table (and shouldn't). In this case, one solution is to add a static route to the laptop's routing table to send all requests destined for 192.168.1.127 out of the interface corresponding to 192.168.1.4. Voila, no ARP request for 192.168.1.127, no problem.
Unfortunately, however, our team is working with some antiquated hardware in place of the "laptop" in the above example that doesn't support adding static routes.
So, in doing some Googling around and reading of past posts on this forum, it seems like layer 2 forwarding is one possible solution here (MCU #1 would be responsible for this). I was thinking of using PPP proxy arp support on MCU #1, but noticed that it was commented out of the lwip ppp implementation in 2015 (commit hash 99bcce78...). The commit message simply reads "PPP, IPCP, removed proxy ARP support". Was curious to know if this is something that, if the surrounding `#define`s were removed, would likely just work, or if there was some underlying implementation issue that led to its removal. Also, any other ideas about how this problem might be resolved otherwise, given the constraints on network topology?
Thanks!