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Traceroute Using an IP Option
Request for Comments: 1393. January 1993. The existing traceroute operates by sending out a packet with a Time To Live (TTL) of 1. The first hop then sends back an ICMP error message indicating that the packet could not be forwarded because the TTL expired. The packet is then resent with a TTL of 2, and the second hop returns the TTL expired. This process continues until the destination is reached. The purpose behind this is to record the source of each ICMP TTL exceeded message to provide a trace of the path the packet took to reach the destination. The advantage of this algorithm, is that every router already has the ability to send TTL exceeded messages. No special code is required. The disadvantages are the number of packets generated (2n, where n is the number of hops), the time it takes to duplicate all the nearer hops with each successive packet, and the fact that the path may change during this process. Also, this algorithm does not trace the return path, which may differ from the outbound path. The proposed traceroute would use a different algorithm to achieve the same goal, namely, to trace the path to a host.
A new IP Traceroute option will be defined. 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). The disadvantage of this method is that the traceroute function will have to be put into the routers.
This RFC was obsoleted by RFC 6814: Formally Deprecating Some IPv4 Options, November 2012.
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