1TRACEPATH(8)                        iputils                       TRACEPATH(8)
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NAME

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

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

14       It traces the network path to destination discovering MTU along this
15       path. It uses UDP port port or some random port. It is similar to
16       traceroute. However, it does not require superuser privileges and has
17       no fancy options.
18
19       tracepath -6 is a good replacement for traceroute6 and classic example
20       of application of Linux error queues. The situation with IPv4 is worse,
21       because commercial IP routers do not return enough information in ICMP
22       error messages. Probably, it will change, when they are updated. For
23       now it uses Van Jacobson's trick, sweeping a range of UDP ports to
24       maintain trace history.
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OPTIONS

27       -4
28           Use IPv4 only.
29
30       -6
31           Use IPv6 only.
32
33       -n
34           Print primarily IP addresses numerically.
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36       -b
37           Print both: Host names and IP addresses.
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39       -l
40           Sets the initial packet length to pktlen instead of 65535 for IPv4
41           or 128000 for IPv6.
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43       -m
44           Set maximum hops (or maximum TTLs) to max_hops instead of 30.
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46       -p
47           Sets the initial destination port to use.
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49       -V
50           Print version and exit.
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OUTPUT

53           root@mops:~ # tracepath -6 3ffe:2400:0:109::2
54            1?: [LOCALHOST]                              pmtu 1500
55            1:  dust.inr.ac.ru                   0.411ms
56            2:  dust.inr.ac.ru        asymm  1   0.390ms pmtu 1480
57            2:  3ffe:2400:0:109::2               463.514ms reached
58                Resume: pmtu 1480 hops 2 back 2
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60
61       The first column shows the TTL of the probe, followed by colon. Usually
62       the value of TTL is obtained from the reply from the network, but
63       sometimes it does not contain the necessary information and we have to
64       guess it. In this case the number is followed by ?.
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66       The second column shows the network hop which replied to the probe. It
67       is either the address of the router or the word [LOCALHOST], if the
68       probe was not sent to the network.
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70       The rest of the line shows miscellaneous information about the path to
71       the corresponding network hop. It contains the value of RTT, and
72       additionally it can show Path MTU when it changes. If the path is
73       asymmetric or the probe finishes before it reaches the prescribed hop,
74       the difference between number of hops in forward and return direction
75       is shown next to the keyword "async". This information is not reliable,
76       e.g. the third line shows asymmetry of 1. This is because the first
77       probe with TTL of 2 was rejected at the first hop due to Path MTU
78       Discovery.
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80       The last line summarizes information about all the paths to the
81       destination. It shows detected Path MTU, amount of hops to the
82       destination and our guess about the number of hops from the destination
83       to us, which can be different when the path is asymmetric.
84

SEE ALSO

86       traceroute(8), traceroute6(8), ping(8).
87

AUTHOR

89       tracepath was written by Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>.
90

SECURITY

92       No security issues.
93
94       This lapidary deserves to be elaborated.  tracepath is not a privileged
95       program, unlike traceroute, ping and other beasts of their kind.
96       tracepath may be executed by everyone who has enough access to the
97       network to send UDP datagrams to the desired destination using the
98       given port.
99

AVAILABILITY

101       tracepath is part of iputils package.
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105iputils 20210722                                                  TRACEPATH(8)
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