I have two Cisco routers (A & B) that reside on the same ethernet hub. Cisco router A is configured with a primary and secondary address. The secondary address is in the same IP range as the IP address for Router B's ethernet interface. Router B's ethernet is configured with only a primary address.
From Router B, I can ping the secondary address of Router A's ethernet and it's serial interface's IP address and beyond.
From Router A, I am not able to ping Router B's ethernet.