Also note that these IPs may sit on interfacs accompanied by 'routable'
IPs, such as the 'secondary' keyword is used in Cisco-Speak (maybe
others as well, I dunno). I've seen cases where customer's use RFC 1918
addreses as the primary and their real addresses as secondaries, so as
to make it difficult to attack the router. TTL exceeded messages then
get returned with the primary IP....
-Chris