ICMP (Internet Control Message Protocol)
TCP/IP suite provide the error and informational messages by the serivce of ICMP. The ICMP messages provide the feedback of the process of IP pakcet in certian conditions. It includes ICMPv4 and ICMPv6
- ICMPv4 The message protocol
- ICMPv6 The same with ICMPv4 but has addtional functionality
Types of Messages
-
Host Reachability
ICMP echo message is used to test the reachablity of a host on a network. The host send a ICMP echo request message to another one, if the destination host is reachable, then it will response with a IMCP echo reply message. The use of this is basis of Ping unititly. - Host or Service Unreachable
When a device receives a pakcet that can not be delivered, it will send a ICMP Destination Unreachable message to notify the source that the destination or service is unreachable. The codes in the messsage indicate why it can’t be delivered.
| ICMPv4 Code | Reason |
|---|---|
| 0 | Net unreachable |
| 1 | Host unreachable |
| 2 | Protocol unreachable |
| 3 | Port unreachable |
| ICMPv6 Code | Reason |
|---|---|
| 0 | No route to destination |
| 1 | Communication with the destination is administritively prohibited |
| 2 | Beyond scope of the source address |
| 3 | Address unreachable |
| 4 | Port unreachable |
- Time Exceeded
If the router receives a packet in which the value of the TTL(Time to Live) decremented to 0, it will discard the packet and send a ICMPv4 time exceeded message to the source.
ICMPv6 is the same with ICMPv4,As oppsed to the TTL value, the factor that determined to discard the pakcet is the vlaue in Hop Limit field.
ICMP Time Exceeded messages are used by traceroute tool.
ICMPv6 Message
ICMPv6 has new features and imporoved functionality which ICMPv4 doesn’t have.
-
Messaging between IPv6 routers and IPv6-enabled devices for allacating ip address
- Router Solicitation (RS) messages
- Router Advertisement(RA) messages
- Messageing between IPv6 devices for duplicate address detection and address resolution.
- Neighbor Solicitation (NS) messages
- Neighbor Advertisement (NA) messages