Traceroute!!!!

[ajitkgiri]

 Hi,

 While tracing some destination, I have always observed that I am getting three times. Why so? I am giving one example below. I have tried to trace google.co.in and got mentioned output. Please reply.

C:\Users\nbgiripr>tracert google.co.in

Tracing route to google.co.in [173.194.112.87]
over a maximum of 30 hops:

  1     2 ms     3 ms    <1 ms  10.127.161.2
  2     1 ms     1 ms     1 ms  10.127.160.2
  3     6 ms     5 ms     7 ms  212.31.208.246

Regards

Ajit

[pavan1279]

I think when you are tracing route to some ip address, it actually pings for 3 times to the next hop and gives the corresponding reply time for each ping. Like, by default, when you try to ping any ip address it gives you reply for 4 times in the same way tracert gives you 3 replys for each hop.

[Joseph W. Doherty]

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Posting

It's because the default is often 3 probes.  On many Cisco devices you can vary the number of probes.

[devils_advocate]

Copied from this Cisco Article which explains both Ping and Traceroute:

http://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-software-releases-121-mainline/12778-ping-traceroute.html

The Traceroute Command

The traceroute command is used to discover the routes that packets actually take when traveling to their destination. The device (for example, a router or a PC) sends out a sequence of User Datagram Protocol (UDP) datagrams to an invalid port address at the remote host.

Three datagrams are sent, each with a Time-To-Live (TTL) field value set to one. The TTL value of 1 causes the datagram to "timeout" as soon as it hits the first router in the path; this router then responds with an ICMP Time Exceeded Message (TEM) indicating that the datagram has expired.

Another three UDP messages are now sent, each with the TTL value set to 2, which causes the second router to return ICMP TEMs. This process continues until the packets actually reach the other destination. Since these datagrams are trying to access an invalid port at the destination host, ICMP Port Unreachable Messages are returned, indicating an unreachable port; this event signals the Traceroute program that it is finished.