Oh, yes – one other thing I discovered working on NMC DOiT scenario 23. I was doing an ICMP debug while pinging between frame-relay spoke R3 & R4 via hub R1. I was seeing some codes come through in the debug that I wasn’t familiar with. I did a little searching on Cisco.com, and came up with this little article regarding ICMPv6 Packet Types and Codes.
Check out this debug output that got my wheels turning on this topic. Here, I’m pinging R4/spoke (FEC0::134:4) from R3/spoke via R1/hub, edited for clarity and brevity. I wanted to know what a “type 137” ICMP message was coming from R1. For the terminally curious, here’s an excerpt from the article I linked to above. “Redirect Message – 137 – Routers send redirect packets to inform a host of a better first-hop node on the path to a destination. Hosts can be redirected to a better first-hop router but can also be informed by a redirect that the destination is in fact a neighbor. The latter is accomplished by setting the ICMP target address equal to the ICMP destination address.”
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FEC0::134:4, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 164/174/212 ms
*Mar 3 05:54:03.710: ICMPv6: Sending echo request to FEC0::134:4
*Mar 3 05:54:03.790: ICMPv6: Received ICMPv6 packet from FE80::20E:83FF:FE08:1270, type 137
*Mar 3 05:54:03.874: ICMPv6: Received ICMPv6 packet from FEC0::134:4, type 129
*Mar 3 05:54:03.874: ICMPv6: Received echo reply from FEC0::134:4
R1#show ipv6 interf bri
Serial1/0 [up/up] FE80::20E:83FF:FE08:1270