[jedi/old/i-menu.htm]
3TGKB-0046

Last Edited :

01-06-05

Revision :

 1.0

What is an ICMP Type Number?

Another question that is asked when configuring TCP/IP security of some sort.

 

The Internet Control Message Protocol (ICMP) has many messages that are identified by a "type" field.

 

Below you can click to see a capture of a ping packet (ICMP) clearly showing that it is ICMP type 8 (0x01)

 

Here is a table with some common ICMP Type Numbers you may need to know.

 

Type Name Comment References
0 Echo Reply Normal Ping reply rfc0792
3 Destination Unreachable Has codes to denote a reason click here to find out more. rfc0792
4 Source Quench Router is busy rfc0792
5 Redirect Shorter Route Discovered rfc0792
8 Echo Request Normal Ping request rfc0792
11 Time Exceeded Too many hops to destination rfc0792
12 Parameter Problem Encapsulated Security Payload rfc0792
30 Traceroute   rfc1393

 

 If you wish to see the whole list then visit - ICMP Type Numbers at http://www.iana.org/assignments/icmp-parameters or have a look at the inline frame below...

 

Some ICMP Type numbers have codes to explain the reason.   Type 3 (Destination Unreachable) has the following codes...

 

Destination Unreachable Codes

            0  Net Unreachable
            1  Host Unreachable
            2  Protocol Unreachable
            3  Port Unreachable
            4  Fragmentation Needed and Don't Fragment was Set
            5  Source Route Failed
            6  Destination Network Unknown
            7  Destination Host Unknown
            8  Source Host Isolated
            9  Communication with Destination Network is Administratively Prohibited
           10  Communication with Destination Host is Administratively Prohibited
           11  Destination Network Unreachable for Type of Service
           12  Destination Host Unreachable for Type of Service
           13  Communication Administratively Prohibited
           14  Host Precedence Violation  
           15  Precedence cutoff in effect 
 

 

I hope this all helps?

 

Regards

Matt Rowston

KB Keywords:  TCP/IP, IP, Protocol Number, Firewall, packet filter, ICMP Type Numbers.