A.  yes there is a implicit deny, as we are only interested in seeing the ICMP debug, and we dont need to apply it on any interface, as we are not filtering any incoming or outgoing traffic, but the debug output only.

Hi Alex,here's more you can try :on the standby router."sh ip route x.x.x.254" , see if recognises the address.check the output of access-list 101 permit icmp any anydebug ip packet detail 101endping x.x.x.254see if the output gives any clues- see if...

yes, you presumed correctly.so, the address a.b.c.254 is bounded to MAC 0000.0c07.ac00there's a thread, i haven't gone through it all,  you can try.https://supportforums.cisco.com/thread/2037773