tracert and traceroute

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The traceroute tool allows you to test the whole path between two nodes with a view to isolating the node or link that is causing the problem.

traceroute

• traceroute is supported on Linux and router operating systems (e.g., Cisco IOS)
  • uses UDP to probe messages by default
    • port 33434 with TTL of 1
  • first hop should reduce the TTL to zero and respond with an ICMP Time Exceeded message
  • then increments the port number and TTL by one and sends a second probe, which should reach the second hop router
  • process repeats until the end node is reached
    • replies with an ICMP Port Unreachable response
  • output shows:
    • number of hops
    • IP address of the ingress interface of the router or host
      • i.e., the interface from which the router receives the probe
    • the time taken to respond to each probe in milliseconds (ms)
  • if no acknowledgement is received within the timeout period,
    • an asterisk is shown against the probe
    • while this could indicate that the router interface is not repsonding,
      • it could also be that the router is configured to drop packets with expired TTLs silently
  • can be configured to send ICMP Echo Request probes rather than UDP by using traceroute -I
  • traceroute -6 or traceroute6 commands are used for IPv6 networks

tracert

• same function is performed on Windows with tracert
  • uses ICMP Echo Request probes by default
  • issues an Echo Request probe with TTL of 1
  • first hop should reduce this to zero and respond with a Time Exceeded response
  • then increments the TTL by one each time to discover the full path
• can be used with several switches:
  • must precede the target IP or host
  • -d to suppress name resolution
  • -h to specify maximum number of hops
    • default is 30
  • -w to specify a timeout in ms
    • default is 4000
    • if, after increasing the value, the destinations are unreachable
      • you probably have a bandwidth issue to resolve
  • -6 to force to use IPv6 instead of IPv4
    • use with host names instead of IP address
    • E.g., tracert -6 www.microsoft.com