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Cannot traceroute using UDP protocol

Posted: Tue Aug 10, 2010 2:13 pm
by inertia
I have got a RB 1000, if i trace route for the open DNS which is 208.67.222.222 using ICMP protocol it works out fine. But if i change the protocol to UDP it can not find the route to open DNS. Also when using ICMP i get a time out in between the route. Can anyone please help me. I am using VOIP phones which use UDP SIP connections and right now they can not make calls because they cant get to DNS.

Re: Cannot traceroute using UDP protocol

Posted: Tue Aug 10, 2010 3:00 pm
by fewi
Where is it being dropped?

Timeouts somewhere in an ICMP trace route are fairly normal. Some providers block ICMP on their equipment. It doesn't necessarily indicate a problem.

Re: Cannot traceroute using UDP protocol

Posted: Tue Aug 10, 2010 4:09 pm
by Chupaka
please post exact results of both traceroutes

Re: Cannot traceroute using UDP protocol

Posted: Tue Aug 10, 2010 4:56 pm
by inertia
I have attached now both traceroute results. The time outs that i am getting are all at the ips that does not belong to my network. And you could see when doing a udp trace route it is showing me that the host is un reachable.

Re: Cannot traceroute using UDP protocol

Posted: Tue Aug 10, 2010 5:04 pm
by Chupaka
well, seems like it means that the host is not answering UDP packets =) and does not send ICMP rejects

Re: Cannot traceroute using UDP protocol

Posted: Tue Aug 10, 2010 6:42 pm
by inertia
If what you are telling is right , when i use icmp and ping 4.2.2.2 from rb1000 it reaches there but breaks multiple times in between the route. How could you define that?

Re: Cannot traceroute using UDP protocol

Posted: Tue Aug 10, 2010 7:26 pm
by fewi
You mean a traceroute to 4.2.2.2 times out on transient hops but reaches the target? The hops the traceroute traverses don't respond to ICMP traceroutes.

When you traceroute to a target, the client first sends out an ICMP traceroute packet with a TTL of 1. The first router in the way receives it, decreases the TTL to 0 and reponds. The client then sends out another ICMP traceroute packet with a TTL of 2. The first router in the way receives it, decreases the TTL to 1 and forwards the packet to the next router. That next router decreases the TTL to 0 and responds. Your client does that until the target router responds, each time increasing the TTL by 1.
If a router in the way doesn't respond to the traceroute packet, the traceroute on that hop will time out. Your client will still send another packet with a higher TTL to investigate the next hop.

But I'm not sure I understood the question right.

Re: Cannot traceroute using UDP protocol

Posted: Tue Aug 10, 2010 7:35 pm
by inertia
I have attached another traceroute. You could better understand my question now.

Re: Cannot traceroute using UDP protocol

Posted: Tue Aug 10, 2010 7:49 pm
by fewi
Then I did understand the question right, and my answer applies.