fabic974 random (binary) wanderings in the philament empires…

Discover network MTU with ping

Decrease the value of -s 1500 :

ping -M do -s 1500 -c 1 vps.fabic.net
PING vps.fabic.net (91.134.136.248) 1500(1528) bytes of data.
ping: local error: Message too long, mtu=1500

--- vps.fabic.net ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms

Until we get a ping reply :

$ ping -M do -s 1464 -c 1 vps.fabic.net
PING vps.fabic.net (91.134.136.248) 1464(1492) bytes of data.
1472 bytes from 248.ip-91-134-136.eu (91.134.136.248): icmp_seq=1 ttl=50 time=239 ms

--- vps.fabic.net ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 239.746/239.746/239.746/0.000 ms

Where man ping for -M pmtudisc_option :

Select Path MTU Discovery strategy. pmtudisc_option may be either :

  • do (prohibit fragmentation, even local one) ;
  • want (do PMTU discovery, fragment locally when packet size is large) ;
  • or dont (do not set DF flag).

Found at ArchLinux: OpenVPN.

EOF