TRACEPATH(8)                        iputils                       TRACEPATH(8)

       tracepath - traces path to a network host discovering MTU along this

       tracepath [-4] [-6] [-n] [-b] [-l pktlen] [-m max_hops] [-p port] [-V]

       It traces path to destination discovering MTU along this path. It uses
       UDP port port or some random port. It is similar to traceroute, only
       does not require superuser privileges and has no fancy options.

       tracepath -6 is good replacement for traceroute6 and classic example of
       application of Linux error queues. The situation with IPv4 is worse,
       because commercial IP routers do not return enough information in ICMP
       error messages. Probably, it will change, when they will be updated.
       For now it uses Van Jacobson's trick, sweeping a range of UDP ports to
       maintain trace history.

           Use IPv4 only..

           Use IPv6 only..

           Print primarily IP addresses numerically.

           Print both of host names and IP addresses.

           Sets the initial packet length to pktlen instead of 65535 for IPv4
           or 128000 for IPv6.

           Set maximum hops (or maximum TTLs) to max_hops instead of 30.

           Sets the initial destination port to use.

           Print version and exit.

           root@mops:~ # tracepath -6 3ffe:2400:0:109::2
            1?: [LOCALHOST]                              pmtu 1500
            1:                   0.411ms
            2:        asymm  1   0.390ms pmtu 1480
            2:  3ffe:2400:0:109::2               463.514ms reached
                Resume: pmtu 1480 hops 2 back 2

       The first column shows TTL of the probe, followed by colon. Usually
       value of TTL is obtained from reply from network, but sometimes reply
       does not contain necessary information and we have to guess it. In this
       case the number is followed by ?.

       The second column shows the network hop, which replied to the probe. It
       is either address of router or word [LOCALHOST], if the probe was not
       sent to the network.

       The rest of line shows miscellaneous information about path to the
       corresponding network hop. As rule it contains value of RTT.
       Additionally, it can show Path MTU, when it changes. If the path is
       asymmetric or the probe finishes before it reach prescribed hop,
       difference between number of hops in forward and backward direction is
       shown following keyword async. This information is not reliable. F.e.
       the third line shows asymmetry of 1, it is because the first probe with
       TTL of 2 was rejected at the first hop due to Path MTU Discovery.

       The last line summarizes information about all the path to the
       destination, it shows detected Path MTU, amount of hops to the
       destination and our guess about amount of hops from the destination to
       us, which can be different when the path is asymmetric.

       traceroute(8), traceroute6(8), ping(8).

       tracepath was written by Alexey Kuznetsov <>.

       No security issues.

       This lapidary deserves to be elaborated.  tracepath is not a privileged
       program, unlike traceroute, ping and other beasts of this kind.
       tracepath may be executed by everyone who has some access to network,
       enough to send UDP datagrams to investigated destination using given

       tracepath is part of iputils package.

iputils s20190709                                                 TRACEPATH(8)
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