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I am stuck at a very strange result after running the command ping -R in a unix environment. To be more specific, I am trying to follow the path to a server and back but there is quite a mismach between the results from running this command and the traceroute to the same server. Why is that? I am already familiar with the concept of ping -R command and have actually read the manual page very thoroughly, however, I had no luck in expldaining to myself why that could happen. Any suggestions would be much appreciated as I am really confused. Thanks

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Is this consistently appearing discrepancy? Remember that the actual route may change between or even in the middle of your trace. –  Adam Zalcman Dec 23 '11 at 0:00
Asymmetric routing? –  joeqwerty Dec 23 '11 at 0:03
@AdamZalcman: yes it is very consistent and the number of hops is small (8) so everything should work as supposed (I think!) –  user726730 Dec 23 '11 at 0:06
@joeqwerty: Well it could be routed asymmetrically, however the forward route should look the same either by using ping -R or traceroute (or am I wrong?) –  user726730 Dec 23 '11 at 0:07
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2 Answers

Ping -r displays outgoing IP addresses, i.e. addresses when leaving the routers, while traceroute displays addresses when entering the routers. If the 9-address limit of ping -r is sufficient to display all the addresses encountered in a round trip, you can see first the addresses opposite to you, then the addresses towards you. With traceroute you only see the addresses towards you.

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Ping uses ICMP, traceroute uses UDP? Not sure why that would make a difference though, it all rides on IP. Does your traceroute have an option to use ICMP ECHO instead of UDP datagrams? If so, try that and see if it gives you the same answer. Maybe per-flow route caching?

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i have already tried using both icmp and udp and the mismatch continues to occur.. so I guess the protocol used is not the problem –  user726730 Dec 23 '11 at 12:51
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