TRACEPATH(8) System Manager's Manual: iputils TRACEPATH(8)
NAME
tracepath, tracepath6 - traces path to a network host discovering MTU along this path
SYNOPSIS
tracepath [-n] [-b] [-l pktlen] [-m max_hops] [-p port] destination
DESCRIPTION
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.
tracepath6 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, sweep‐
ing a range of UDP ports to maintain trace history.
OPTIONS
-n Print primarily IP addresses numerically.
-b Print both of host names and IP addresses.
-l Sets the initial packet length to pktlen instead of 65535 for tracepath or 128000 for tracepath6.
-m Set maximum hops (or maximum TTLs) to max_hops instead of 30.
-p Sets the initial destination port to use.
OUTPUT
root@mops:~ # tracepath6 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 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 correspinding network hop. As rule it con‐
tains 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 asym‐
metry of 1, it is because the first probe with TTL of 2 was rejected at the first hop due to Path MTU Discov‐
ery.
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 differ‐
ent when the path is asymmetric.
SEE ALSO
traceroute(8), traceroute6(8), ping(8).
http://www.skbuff.net/iputils/iputils-current.tar.bz2.
iputils-160308 TRACEPATH(8)
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