Traceroute

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Image:Winxp-tracert.png traceroute (tracepath on modern Linux systems, tracert on Windows operating system) is a computer network tool used to determine the route taken by packets across an IP network.

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Implementation

traceroute works by increasing the "time to live" value of each successive packet sent. The first packet has a time to live (TTL) value of one, the second two, and so on. When a packet passes through a host, normally the host decrements the TTL value by one, and forwards the packet to the next host. When a packet with a TTL of one reaches a host, the host discards the packet and sends an ICMP time exceeded (type 11) packet to the sender. The traceroute utility uses these returning packets to produce a list of hosts that the packets have traversed en route to the destination. traceroute may not list the real hosts, it indicates that the first host is at one hop, the second host at two hops. IP does not guarantee that all the packets take the same route.

On modern Unix and Linux-based operating systems, the traceroute utility by default uses UDP datagrams with a destination port number starting at 33434. The traceroute utility usually has an option to specify use of ICMP echo request (type 8) instead, as used by the Windows tracert utility. There are also traceroute implementations that use TCP packets, such as tcptraceroute or Layer Four Trace. A new utility, pathping, was introduced with Windows NT, combining ping and traceroute functionality. Matt's Trace Route (MTR) is an enhanced version of icmp traceroute available for Unix and Windows systems under a GNU license. All implementations of traceroute rely on ICMP (type 11) packets being sent to the originator.

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Example

Estonia to the United States. 195.80.96.219 (kauge.aso.ee) to 130.94.122.199 (larousse.wikipedia.org). 

1   kauge.aso.ee
2   et-gw.aso.ee
3   kjj-bb2-fe-0-1-4.ee.estpak.ee
4   noe-bb2-ge-0-0-0-1.ee.estpak.ee
5   s-b3-pos0-3.telia.net
6   s-bb1-pos1-2-0.telia.net
7   adm-bb1-pos1-1-0.telia.net
8   adm-b1-pos2-0.telia.net
9   p4-1-2-0.r00.amstnl02.nl.bb.verio.net
10  p4-0-3-0.r01.amstnl02.nl.bb.verio.net
11  p4-0-1-0.r80.nwrknj01.us.bb.verio.net
12  p4-0-3-0.r00.nwrknj01.us.bb.verio.net
13  p16-0-1-1.r20.mlpsca01.us.bb.verio.net
14  xe-1-2-0.r21.mlpsca01.us.bb.verio.net
15  xe-0-2-0.r21.snjsca04.us.bb.verio.net
16  p64-0-0-0.r21.lsanca01.us.bb.verio.net
17  p16-3-0-0.r01.sndgca01.us.bb.verio.net
18  ge-1-2.a03.sndgca01.us.da.verio.net
19  larousse.wikipedia.org
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Origins

The traceroute man page states that the original traceroute program was written by Van Jacobson in 1987 from a suggestion by Steve Deering, with particularly cogent suggestions or fixes from C. Philip Wood, Tim Seaver and Ken Adelman.

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Uses

Traceroute is often used for network troubleshooting. By showing a list of routers traversed, it allows the user to identify the path taken to reach a particular destination on the network. This can help identify routing problems or firewalls that may be blocking access to a site. Traceroute is also used by penetration testers to gather information about network infrastructure and IP ranges around a given host.

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External links

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.
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