3 Replies Latest reply: Nov 26, 2010 2:53 PM by Scott Morris - CCDE/4xCCIE/2xJNCIE RSS

    Traceroute - packet drop

    Nilesh W

      Hi friends,

       

      One query about traceroute.

      If packet drops getting on any hope while doing  traceroute to destination.

      Is it issue with ISP or might be ping blocked by ISP on that hope.

      Is ISP does these things in bewteen hopes.

       

      Please see the below scenaro.

       

      Getting packet drop 4th and 10th hope.  Ignore packet drop after 20th hope.It is acceptable as destination tracert completed at 19th hope.

      Real IP's hided in below example.

       

        1    14 ms     2 ms     2 ms  192.168.1.1

        2     4 ms     3 ms     4 ms  172.16.10.47
        3     8 ms     6 ms     6 ms   1.1.1.1
        4     *              *        5 ms    2.2.2.2
        5   146 ms   146 ms   146 ms 
      ]
        6   137 ms   137 ms   137 ms 
      ]
        7   137 ms   137 ms   137 ms

       

        8   138 ms   138 ms   138 ms

       

        9   226 ms   247 ms   226 ms

       

      10     *        *        *     Request timed out.
      11   222 ms   222 ms   222 ms

      12   274 ms   273 ms   274 ms 

      13   278 ms   274 ms   274 ms

      14   273 ms   274 ms   274 ms

      15   275 ms   274 ms   277 ms

      16   273 ms   274 ms   277 ms

      17   277 ms   274 ms   274 ms

      18   276 ms   276 ms   272 ms

      19   273 ms   277 ms   277 ms        11.12.13.14     Required host tracert completed here.

      20     *        *        *     Request timed out.
      21     *        *        *     Request timed out.
      22     *        *        *     Request timed out.
      23     *        *        *     Request timed out.
      24     *        *        *     Request timed out.
      25     *        *        *     Request timed out.
      26     *        *        *     Request timed out.
      27     *        *        *     Request timed out.
      28     *        *        *     Request timed out.
      29     *        *        *     Request timed out.
      30     *        *        *     Request timed out.

      Trace complete.

       

      Regards,

       

      Nilesh W

        • 1. Re: Traceroute - packet drop
          Scott Morris - CCDE/4xCCIE/2xJNCIE

          Well, we have to understand a little bit about how traceroute works.  And part of that will depend on what OS we are talking about!

           

          Micro$oft tends to use ICMP with a variable TTL, so it's JUST like doing a ping.  Some devices will filter pings, so you may have  a whole slew that simply don't respond.

           

          Unix (and Cisco IOS is a derivative thereof) use a UDP packet with variable TTL.  Again, there may be filter issues involved.

           

          Either way though, your interim routers SHOULD see that TTL doesn't allow them to forward and respond with an ICMP - TTL-Exceeded message.  If a router/device in the middle has "no ip unreachables" configured, then it will NOT respond, and that's expected behavior.

           

          When you reach the end station, assuming there's nothing listening to the UDP port being used, then you should get an ICMP - Port-unreachable message back and that's how you know it's completed.

           

          If your traceroute properly completed, you'd have it end.  The fact that you have "request timed out" messages AFTER you say it completed tells me that it did not properly complete due to some filtering/ACL.

           

          HTH,

           

          Scott

          • 2. Re: Traceroute - packet drop
            Nilesh W

            Hi Scott,

             

            Thanks for detail expalination.

             

            ISP might be configured no ip reachables commands .So I do not worry about it.

             

            Regards,

             

            Nilesh W

            • 3. Re: Traceroute - packet drop
              Scott Morris - CCDE/4xCCIE/2xJNCIE

              Yup...  As long as your end result is good, or packets get where they need to go, then you're good. 

               

              Scott