"traceroute" - Trace Route to Remote Host

Ubuntu Tutorials - Herong's Tutorial Examples

∟"traceroute" - Trace Route to Remote Host

This section provides a tutorial example on how to use 'traceroute' command to trace route (or gateways) between the local host and a given remote host.

"traceroute" is a command line tool that allows to trace route between the local host and a given remote host. "traceroute" utilizes the IP protocol "TTL (Time To Live)" field and attempts to elicit an ICMP TIME_EXCEEDED (Time To Live Exceeded) response from each gateway along the path to some host.

First install "traceroute" using the APT command.

herong$ sudo apt install traceroute

Then try to find the network route to bing.com.

herong$ traceroute bing.com 

 1  _gateway (10.0.0.1)  2.878 ms  2.889 ms  3.219 ms
 2  75.138.242.57 (75.138.242.57)  23.509 ms  23.428 ms  23.384 ms
 3  po-rur303.newyork.comcast.net (...)  19.627 ms  19.591 ms  21.377 ms
 4  * * *
 5  * be-21-0.ibr02.by4.ntwk.msn.net (104.44.21.7)  30.091 ms *
 6  be-21-0.ibr02.by4.ntwk.msn.net (104.44.21.7)  32.414 ms  34.056 ms *
 7  * 51.10.4.48 (51.10.4.48)  33.945 ms  33.199 ms
 8  51.10.4.50 (51.10.4.50)  33.133 ms 
    be-5-0.ibr01.nyc30.ntwk.msn.net (104.44.7.102)  27.300 ms *
 9  ae25-0.ear05.nyc30.ntwk.msn.net (104.44.33.216)  35.497 ms 
    be-5-0.ibr01.nyc30.ntwk.msn.net (104.44.7.102)  23.759 ms 
    ae24-0.ear04.nyc30.ntwk.msn.net (104.44.33.206)  25.149 ms
10  * * *
11  * * *
12  * * *
13  * * *
14  * * *

Here is how to read the output.

The first number on each output line is the TTL value set on outgoing ICMP ECHO_REQUEST messages.
For each TTL value, "traceroute" fires 3 ICMP ECHO_REQUEST messages.
3 response received from each TTL value are reported on the same line.
"2 75.138.242.57 (75.138.242.57) 23.509 ms 23.428 ms 23.384 ms" tells us that 3 TTL=2 requests were responded by the same gateway, 75.138.242.57.
"4 * * *" tells us that no responses were received for all 3 TTL=4 requests.
"5 * be-21-0.ibr02.by4.ntwk.msn.net (104.44.21.7) 30.091 ms *" tells us that the first and the third requests for TTL=5 were not responded, while the second request was responded.
"9 ae25-0.ear05.nyc30.ntwk.msn.net (104.44.33.216) 35.497 ms be-5-0.ibr01.nyc30.ntwk.msn.net (104.44.7.102) 23.759 ms ae24-0.ear04.nyc30.ntwk.msn.net (104.44.33.206) 25.149 ms" tells us that 3 TTL=9 requests were responded by 3 different gateways.

Again, Internet routes are not static. This is why 3 TTL=9 requests were responded by 3 different gateways.

If an ECHO_REQUEST did not receive a response (an ECHO_RESPONSE, or an TIME_EXCEEDED), it is usually the result of gateway's setting to not respond on TIME_EXCEEDED error.