I am toying with trace route, my application send a ICMP echo request with a ttl of 0 every time i receive a time exceeded message i increment the ttl by one and resent the package, but what happens is I have 2 routers on my network i can trace the route through these router but third hop always ends up being one of the open dns servers same ip every time no matter where i traceroute to. AFAIK this is the correct traceroute implementation, can anyone tell me what i am doing wrong?
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The first packet should have a ttl of 1, not 0. It sounds to me like a route is forwarding all ICMP request to a specific location. Take your app to a different location and see if it works there. – dbasnett Apr 05 '10 at 21:44
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It's possible that both routers connect to the same peer, and you'd get the described behaviour.
Without more info, it's not really possible to answer your question.
Frank Shearar
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"routers connect to the same peer" can you explain what you meant by that? – Hamza Yerlikaya Mar 31 '10 at 13:20
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I mean that there's nothing particularly strange about your two routers routing to the same machine. – Frank Shearar Mar 31 '10 at 13:53
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While it's hard to say without any additional information, the best bet would be to install some packet sniffer — probably wireshark / www.wireshark.org — and compare the icmp packets — what goes on the wire with your traceroute, and what does the system /usr/bin/traceroute (or \windows\system32\tracert) send.
Einar Lielmanis
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If you have a NAT router on the path it can screw up your nicely adjusted TTL's
joveha
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i have two routers on the path one is mine which i use inside the room the other belongs to the building i'm living in which very much like to mess with my connection, but regular traceroute works fine in this situation. – Hamza Yerlikaya Mar 31 '10 at 15:08
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I see. This "open dns server", is that also a router "in the building" or somewhere close? Have you tried using the regular traceroute command (with ICMP and UDP) to see if the result differ? Without more information I would conclude that the third router, which also acts as DNS, is blocking your packets - possibly because it's also NAT'ing. – joveha Mar 31 '10 at 16:04
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Are you saying that if you use the traceroute command it works, but your app that is mimicking traceroute doesn't? Seeing code might help us help you. – dbasnett Apr 05 '10 at 21:46