TRACEROUTE.md

Guide: traceroute

Packets move though IP networks by hoping though various appliances. Perhaps the most important appliance of note in terms of packet forwarding are routers. Knowing if 2 points in a network can communicate is something that can easily be determined with tools such as ping and hping3, but knowing any details about the route they traversed the network via is typically less visible. Traceroute uses the IP header's TTL field and the expected ICMP TIME_EXCEEDED responses to determine each hop a packet takes on its journey.

Traceroute can be used with the command "traceroute" followed by any flags.

• -f: The TTL of the first probe (each probe increments this by 1)
• -m: The maximum TTL to increment to

📖 There is more traceroute can do, see the traceroute man page for more!

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Example: Tracing a Journey

• To determine the IP addresses of any routers between your device and lancaster.ac.uk, use traceroute like so:

  traceroute lancaster.ac.uk
  

• The output should look something like:

  traceroute to lancaster.ac.uk (148.88.65.80), 30 hops max, 60 byte packets
   1  gateway (X.X.X.X)  0.228 ms  0.187 ms  0.181 ms
   2  X.X.X.X (X.X.X.X)  0.401 ms  0.347 ms  0.375 ms
   3  jips-ipv6.lancs.ac.uk (194.80.33.17)  5.399 ms  5.601 ms  5.375 ms
   4  isag03.is-core01.rtr.lancs.ac.uk (148.88.253.153)  5.341 ms  6.026 ms  5.527 ms
   5  www.lancs.ac.uk (148.88.65.80)  0.695 ms !X  0.697 ms !X  0.653 ms !X
  

  This output shows each router encountered by the packet on the way to lancaster.ac.uk, including the local gateway.