I have a Windows PC connected to a LAN segment. The same LAN segment contains a WAN router with a serial interface.
I issue a traceroute from the Windows PC to a device reachable through the WAN. I'd expect the WAN router to respond that the first hop is the IP address on the LAN interface. Instead, the router indicates the first hop in the IP address on the WAN interface. What would cause the router to respond to the traceroute with the IP address of an interface other than the one used to reach the client?