Explanation on traceroute

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Sep 14th, 2008
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When I used traceroute for troubleshooting I got an output which I never came across like 3 IP's in the first hop. Can some one explain the meaning of the following outputs.


6513-2#traceroute 192.168.151.65


Type escape sequence to abort.

Tracing the route to 192.168.151.65


1 192.168.160.117 0 msec

192.168.160.173 0 msec

192.168.168.253 0 msec

2 *

192.168.160.181 0 msec 0 msec

3 192.168.151.65 0 msec 4 msec 0 msec

6513-2#


Thanks

Rajesh

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Giuseppe Larosa Sun, 09/14/2008 - 23:21
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Hello Rajesh,

Cisco traceroute sends UDP packets with a high port number.

First try is done by using TTL=1, then 3 attempts are done using process switching.

By using process switching if multiple paths exist they are used in sequence.


in your case at least 3 different ip next hops exist for ip address 192.168.151.65

if you do sh ip route 192.168.151.65

you should see at least three paths via the 3 next hops shown in the trace route.


then traceroute increments the TTL to 2 and sends out again three packets and so on


the end host will send back an icmp protocol unreachable while intermediate devices will send back an icmp TTL expired.


Hope to help

Giuseppe


adahiya Sun, 09/14/2008 - 23:29
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It happens when there are various next hops available to reach the destination.


For Eg.


R1-------R2-----3ckts(load balancing)-----R3


If u run the traceroot on R3 to reach R1 u will get the same result as u got


Thanks



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