Icmp

[tarun_cisco]

Please suggest port number used by icmp and traceroute.

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[Somasundaram Jayaraman]

Hi,

In Unix operating systems, the traceroute utility by default uses (UDP) with destination port numbers  from 33434 to 33534

++ ICMP (ping, trace) is a layer 3 protocol suite within the TCP/IP suite,  doesnt test any layer 4 or above functions, therefore, it has no TCP/UDP  layer 4 port number.The sub protocols within it do.

++ You can block echo  replies by closing port 7. That is how you get to be not  pinged on the  net.

++ ICMP does not use ports. However, it does have various ICMP types, the most common being echo reply (type 0), echo request (type,  and Destination Unreachable (type 3).  Because of the numbers, you'll  often hear "it's trying to connect on port 0", when actually it's an  echo reply packet.

Hope this helps

Cheers

Somu

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[smogra]

Protocol ICMP is the part of the IP layer and ICMP messages are transmitted within IP datagrams. IP datagram

consists of the IP header (20 bytes) and ICMP message. The first byte of the ICMP message contains the type field. For example, Ping uses the messages echo reply (type 0) and echo request (type 8). The Traceroute sends UDP datagrams. Destination UDP port should be chose as an unlikely value, so that it is impossible that any destination application uses this port. UDP destination side sends an ICMP message port unreachable (type 3, code 3). If TTL is 0 in the received datagram the router sends back the ICMP message time exceeded (type 11, code 0). ICMP messages

are exchanged between hosts without port numbers.

Cheers

Sweta