ICMP

Internet Control Message Protocol

Code	ICMPv4	ICMPv6
0	Net unrecheable	No route to destination
1	Host unrecheable	Communication is administratively prohibited
2	Protocol unrecheable	Beyond scoupe of source address
3	Port unrecheable	Address unrecheable
4	Fragmentation Needed and D.F.	Port unrecheable

Time Exceeded

Router Advertisement (RA)
- Every 200s broadcasted to IPv6 hosts
- Sends Prefix and default gateway link local
- Router: I am an IPv6 router, this is my prefix, use SLAAC/RID to generate a GUA, and this is my default gateway link-local address: …
Router Solicitation (RS)
- Sent if host needs RA message for IPv6 configuration
- Host: Hey! Is there any IPv6 router here? I need it to generate an IPv6 address.
Neighbour Solicitation (NS)
- Sent to a host's address to check address uniqueness
- If host receives NA message, it regenerates its IPv6 interface ID (randomly) and checks again
- “Hey you! Are you there? Do you have this address already?”
Neighbour Advertisement (NA)
- Reply meant for NS messages
- “Hey, I'm using this address already! Use another one!”