tracepath

What it does

How to write it

tracepath [-4] [-6] [-n] [-b] [-l PKTLEN] [-m MAX_HOPS] [-p PORT] DESTINATION

Most used

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$ run as a normal user# run as root (or with sudo)

1. 1Path to a host

   $tracepath -n www.redhat.com
    1?: [LOCALHOST]                      pmtu 1500
    1:  192.168.122.1                                         0.512ms
    2:  10.0.0.1                                              2.104ms
    3:  no reply
   ...

   "no reply" = a router that does not answer (common).

2. 2Names and addresses

   $tracepath -b server2.example.com

   Shows both for each hop.

3. 3Find the path MTU

   $tracepath -n 10.20.0.5 | grep pmtu

   A pmtu under 1500 explains hanging SSH or HTTPS over VPN.

4. 4IPv6 path

   $tracepath -6 -n 2001:db8:10::1

   Check IPv6 routes separately from IPv4.

5. 5Limit the hops

   $tracepath -n -m 5 8.8.8.8

   Only the first part of the path (your own network).

6. 6Compare with the routing table

   $ip route get 8.8.8.8
   8.8.8.8 via 192.168.122.1 dev enp1s0 src 192.168.122.10 uid 1000

   The first hop must be this gateway.

7. 7Check if traffic goes through the VPN

   $tracepath -n 10.50.1.10

   The first hop should be the VPN address, not the home router.

8. 8Save the path for a ticket

   $tracepath -n www.example.com > /tmp/path-$(date +%F).txt

   Give it to the network or hosting team.

9. 9Use a fixed port

   $tracepath -p 33434 -n server2

   Some firewalls only allow certain UDP ports.

10. 10When tracepath stops early

    $tracepath -n 192.168.200.5

    Endless "no reply" after hop 1: no route or a firewall after your gateway.

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