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on my Linux box, traceroute does not work. the output is like this:

$ traceroute google.com

traceroute to google.com (209.85.231.104), 30 hops max, 52 byte packets
1  * * *
2  * * *
3  * * *
4  * * *

Can anyone tell me why its not working? any possible reasons behind it?

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4 Answers 4

it could be that a firewall upstream from you is blocking the UDP packets Traceroute

On modern Unix-like operating systems, the traceroute utility by default uses UDP datagrams with destination ports numbering from 33434 to 33534.

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$ is more likely unix prompt rather than windows one and windows traceroute command is tracert. And the question tells about Linux... –  radius Jun 20 '10 at 20:40
    
i realised this so i edited the answer. –  lalalalalalala Jun 20 '10 at 20:45
    
I thought trace route used ICMP packets. I did not know that unix based systems use UDP. Learn something new everyday. –  dbasnett Jun 21 '10 at 12:32

This is probably because icmp TIME_EXCEEDED answer is filtered by the router/firewall that you use as default gateway or by your Linux system itself

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Try to use -T (tcp) or -U (udp) to bypass firewall.
Some routers/firewall don't let icmp echo pass trough, that's why you'd use those 2 to by pass them.
Anyway, contrary as stated in wikipedia, on my debian boxes traceroute still uses icmp packets and not udp.

EDIT

I was wrong...it uses udp...the icmp coming back are for an unreachable port...sorry

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By default, traceroute uses high UDP ports for tracing hosts. However, sometime firewalls block these UDP ports.

Try to add the "-I" (uppercase i) parameter to the command line, eg:

traceroute www.google.it -I

This will use ICMP instead of UDP for tracing hosts.

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