Manual: tracepath

TRACEPATH(8)						   iputils						TRACEPATH(8)

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

SYNOPSIS

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

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

       tracepath -6 is a 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 are updated. For now it uses Van Jacobson's trick, sweeping a range of UDP ports
       to maintain trace history.

OPTIONS
       -4
	   Use IPv4 only.

       -6
	   Use IPv6 only.

       -n
	   Print primarily IP addresses numerically.

       -b
	   Print both: Host names and IP addresses.

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

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

       -p
	   Sets the initial destination port to use.

       -V
	   Print version and exit.

OUTPUT
	   root@mops:~ # tracepath -6 3ffe:2400:0:109::2
	    1?: [LOCALHOST]				 pmtu 1500
	    1:	dust.inr.ac.ru			 0.411ms
	    2:	dust.inr.ac.ru	      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 the TTL of the probe, followed by colon. Usually the value of TTL is obtained from the reply
       from the network, but sometimes it does not contain the 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 the address of the router or the
       word [LOCALHOST], if the probe was not sent to the network.

       The rest of the line shows miscellaneous information about the path to the corresponding network hop. It contains the
       value of RTT, and additionally it can show Path MTU when it changes. If the path is asymmetric or the probe finishes
       before it reaches the prescribed hop, the number of hops in return direction is shown next to the keyword "asymm".
       This information is not reliable, e.g. the third line shows asymmetry of 1. This 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 paths to the destination. It shows detected Path MTU, amount of
       hops to the destination and our guess about the number of hops from the destination to us, which can be different
       when the path is asymmetric.

HANDLING ERRORS
       In case of errors tracepath prints short error code.
       ┌─────────────┬──────────────┬─────────────────────────────────┐
       │ Output	     │ Code	    │ Meaning			      │
       ├─────────────┼──────────────┼─────────────────────────────────┤
       │ !A	     │ EACCES	    │ Communication administratively  │
       │	     │		    │ prohibited		      │
       ├─────────────┼──────────────┼─────────────────────────────────┤
       │ !H	     │ EHOSTUNREACH │ Destination host unreachable    │
       ├─────────────┼──────────────┼─────────────────────────────────┤
       │ !N	     │ ENETUNREACH  │ Destination network unreachable │
       ├─────────────┼──────────────┼─────────────────────────────────┤
       │ !P	     │ EPROTO	    │ Destination protocol	      │
       │	     │		    │ unreachable		      │
       ├─────────────┼──────────────┼─────────────────────────────────┤
       │ pmtu N	     │ EMSGSIZE	    │ Message too long		      │
       ├─────────────┼──────────────┼─────────────────────────────────┤
       │ reached     │ ECONNREFUSED │ Connection refused	      │
       ├─────────────┼──────────────┼─────────────────────────────────┤
       │	     │ ETIMEDOUT    │ Connection timed out	      │
       ├─────────────┼──────────────┼─────────────────────────────────┤
       │ NET ERROR N │		    │ Any other error		      │
       └─────────────┴──────────────┴─────────────────────────────────┘

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

AUTHOR
       tracepath was written by Alexey Kuznetsov .

SECURITY
       No security issues.

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

AVAILABILITY
       tracepath is part of iputils package.

iputils 20250605												TRACEPATH(8)