1TRACEPATH(8) System Manager's Manual: iputils TRACEPATH(8)
2
6 tracepath, tracepath6 - traces path to a network host discovering MTU
7 along this path
8
10 tracepath [ -n] [ -l pktlen] destination [ port]
11
14 It traces path to destination discovering MTU along this path. It uses
15 UDP port port or some random port. It is similar to traceroute, only
16 does not not require superuser privileges and has no fancy options.
17 tracepath6 is good replacement for traceroute6 and classic example of
19 application of Linux error queues. The situation with tracepath is
20 worse, because commercial IP routers do not return enough information
21 in icmp error messages. Probably, it will change, when they will be
22 updated. For now it uses Van Jacobson's trick, sweeping a range of UDP
23 ports to maintain trace history.
24
26 -n Do not look up host names. Only print IP addresses numerically.
27 -l Sets the initial packet length to pktlen instead of 65536 for
29 tracepath or 128000 for tracepath6.
30
32 root@mops:~ # tracepath6 3ffe:2400:0:109::2
33 1?: [LOCALHOST] pmtu 1500
34 1: dust.inr.ac.ru 0.411ms
35 2: dust.inr.ac.ru asymm 1 0.390ms pmtu 1480
36 2: 3ffe:2400:0:109::2 463.514ms reached
37 Resume: pmtu 1480 hops 2 back 2
38 The first column shows TTL of the probe, followed by colon. Usually
40 value of TTL is obtained from reply from network, but sometimes reply
41 does not contain necessary information and we have to guess it. In this
42 case the number is followed by ?.
43 The second column shows the network hop, which replied to the probe.
45 It is either address of router or word [LOCALHOST], if the probe was
46 not sent to the network.
47 The rest of line shows miscellaneous information about path to the cor‐
49 respinding hetwork hop. As rule it contains value of RTT. Addition‐
50 ally, it can show Path MTU, when it changes. If the path is asymmetric
51 or the probe finishes before it reach prescribed hop, difference
52 between number of hops in forward and backward direction is shown fol‐
53 loing keyword async. This information is not reliable. F.e. the third
54 line shows asymmetry of 1, it is because the first probe with TTL of 2
55 was rejected at the first hop due to Path MTU Discovery.
56 The last line summarizes information about all the path to the destina‐
58 tion, it shows detected Path MTU, amount of hops to the destination and
59 our guess about amount of hops from the destination to us, which can be
60 different when the path is asymmetric.
61
63 traceroute(8), traceroute6(8), ping(8).
64
66 tracepath was written by Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>.
67
69 No security issues.
70 This lapidary deserves to be elaborated. tracepath is not a privileged
72 program, unlike traceroute, ping and other beasts of this kind. tra‐
73 cepath may be executed by everyone who has some access to network,
74 enough to send UDP datagrams to investigated destination using given
75 port.
76
78 tracepath is part of iputils package and the latest versions are
79 available in source form at http://www.skbuff.net/iputils/iputils-cur‐
80 rent.tar.bz2.
81iputils-071127 22 March 2017 TRACEPATH(8)