MTU

Sous linux

Lancer la commande suivante

ping -M do -s 1500 adresse_d_une_machine

PING www.celeste.fr (83.142.144.99) 1500(1528) bytes of data.
From webaps.airaps.local (172.16.43.103) icmp_seq=1 Frag needed and DF set (mtu = 1492)
From webaps.airaps.local (172.16.43.103) icmp_seq=1 Frag needed and DF set (mtu = 1492)
From webaps.airaps.local (172.16.43.103) icmp_seq=1 Frag needed and DF set (mtu = 1492)
From webaps.airaps.local (172.16.43.103) icmp_seq=1 Frag needed and DF set (mtu = 1492)
From webaps.airaps.local (172.16.43.103) icmp_seq=1 Frag needed and DF set (mtu = 1492)
From webaps.airaps.local (172.16.43.103) icmp_seq=1 Frag needed and DF set (mtu = 1492)
From webaps.airaps.local (172.16.43.103) icmp_seq=1 Frag needed and DF set (mtu = 1492)
From webaps.airaps.local (172.16.43.103) icmp_seq=1 Frag needed and DF set (mtu = 1492)

On peut noter le mtu = 1492

Sous FreeBSD se sera la commande

ping -D -s 1500 adresse_ip
ping: sendto: Message too long

On refait alors un test avec cette valeur - 28 (je sais plus pourquoi le 28 …

ping -M do -s 1464 www.celeste.fr 

et ca marche ;)

PING www.celeste.fr (83.142.144.99) 1464(1492) bytes of data.
1472 bytes from www2.celeste.fr (83.142.144.99): icmp_seq=1 ttl=59 time=75.5 ms
1472 bytes from www2.celeste.fr (83.142.144.99): icmp_seq=2 ttl=59 time=75.9 ms
1472 bytes from www2.celeste.fr (83.142.144.99): icmp_seq=3 ttl=59 time=76.3 ms

--- www.celeste.fr ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 75.543/75.936/76.324/0.390 ms

Un petit coup de

ifconfig eth0 mtu 1492

Et voila, votre interface est maintenant réglé, penser à modifier votre fichier /etc/network/interfaces pour que cette valeur de mtu soit prise en compte lors du redémarrage de la machine.