tracepath

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 difference between number of hops in
       forward and return direction is shown next to the keyword
       "async". 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.

AUTHOR

       tracepath was written by Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>.

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.

Example:

tracepath command without any option: It will print the general syntax of the command along with the various options that can be used with the tracepath command as well as gives a brief description about each option.
In the following example using tracepath command we are trying to trace path to destination for google.com.
```
tracepath www.google.com
```

Options:

tracepath -n: This option prints primarily IP addresses numerically.Example:
```
tracepath -n www.google.com
```
tracepath -b: This option print both of host names and IP addresses.Example:
```
tracepath -b www.google.com
```
tracepath -l : This option sets the initial packet length to pktlen instead of 65535 for tracepath or 128000 for tracepath6.Example:
```
tracepath -l 29 www.google.com
```
tracepath -m : This option will set maximum hops (or maximum TTLs) to max_hops instead of 30.Example:
```
tracepath -m 31 www.google.com
```
tracepath -p: This option will set the initial destination port to use.Example:
```
tracepath -p 8080 www.google.com
```