|IP option 18, Traceroute|
|Protocol type:||Connectionless network layer protocol.|
|Option length:||12 bytes.|
|Related ICMP message:||Traceroute.|
|Links:||IANA: IP option numbers.|
RFC 1393, page 2:
The presence of this option in an ICMP Echo (or any other) packet, hereinafter referred to as the outbound packet, will cause a router to send the newly defined ICMP Traceroute message to the originator of the outbound packet. In this way, the path of the outbound packet will be logged by the originator with only n+1 (instead of 2n) packets. This algorithm does not suffer from a changing path and allows the response to the outbound packet, hereinafter refered to as the return packet, to be traced provided the outbound packet's destination preserves the IP Traceroute option in the return packet.
|MAC header||IP header||IP option 18|
IP option 18:
|Outbound Hop Count||Return Hop Count|
|Originator IP Address|
Type. 8 bits. Set to 82.
C, Copy flag. 1 bit. Cleared to 0.
This option is not to be copied into all fragments.
Class. 2 bits. Set to 2.
A debugging and measurement option.
Option. 5 bits. Set to 18.
The IP option number.
Set to 12.
Total length of the option.
An arbitrary number used by the originator of the outbound packet to identify the ICMP Traceroute messages. It is NOT related to the ID number in the IP header.
Outbound Hop Count.
The number of routers through which the outbound packet has passed. This field is not incremented by the outbound packet's destination.
Return Hop Count.
The number of routers through which the return packet has passed. This field is not incremented by the return packet's destination.
Originator IP Address.
The IP address of the originator of the outbound packet. This is needed so routers can know where to send the ICMP Traceroute message for return packets. It is also needed for outbound packets which have a Source Route option.
[RFC 1393] Traceroute Using an IP Option.