Regarding drop in tracert

[ncnaveen_arasu]

Dear team,

why do we get a drop in between tracert and even trace completes.

NaveenC:\Documents and Settings\Amrut>tracert -d www.google.co.in

Tracing route to www.google.co.in [74.125.236.119]
over a maximum of 30 hops:

  1    <1 ms    <1 ms    <1 ms  164.100.80.33
  2     1 ms     1 ms    <1 ms  10.255.232.38
  3    37 ms    10 ms    38 ms  10.255.238.237
  4     9 ms    10 ms    37 ms  10.255.221.225
  5    10 ms     *        9 ms  10.255.222.34
  6    11 ms    12 ms    11 ms  115.249.209.6
  7     *        *        *     Request timed out.
  8     *       25 ms     *     72.14.212.118
  9    27 ms     *        *     209.85.241.52
 10    25 ms     *       26 ms  216.239.48.177
 11    26 ms     *       25 ms  74.125.236.119

Trace complete.


Thanks & Regards,

Naveen

[Steve Fuller]

Hi,

You're probably seeing drops for two reasons here.

Where you see a single probe dropped e.g., hop 5 in the output, this is caused by ICMP rate limiting on the device that is responding. Cisco routers for example will only respond with one ICMP unreachable message every 500-ms.

Where you see Request Timeout such as that in hop 7, the device along the path is most likely configured not to respond with an ICMP error message.

The reason the trace then goes on to complete is that the TTL in the IP header is increased for each successive probe, and so no longer expires at the point that did not respond, but one, two, three etc., hops further along the path towards the destination.

The Cisco document Using the traceroute Command on Operating Systems provides details of how traceroute works and also goes into the differences in operation between Cisco IOS, Microsoft Windows etc.

Regards