MTU
Sauter à la navigation
Sauter à la recherche
The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.
Les problèmes de MTU, c'est une sombre histoire de taille de paquets IP plus ou moins bien découpés/recollés. Ça nous a bien ennuyés pour configurer un accès VPN - sans réelle solution au final. Quelques notes pour plus tard:
- on d'un ICMP unreachable, R1 initialise le MTU à 1000-24=976 octets [1]
mturoute.exe -m 1425 10.10.0.1 -> déconnexion # ICMP payload of 1423 bytes suceeded. # ICMP payload of 1424 bytes failed.. mturoute.exe -m 1424 10.10.0.1 # -> OK (behind Wanadoo)
- man iptables: TCPMSS / (usually limiting it to your outgoing interface's MTU minus 40) => where does "40" comes from?
- my pptpd-options
#MTU stuff # 1500 is common for PPP # GRE adds a 24-bit header # => 1476 # According to my tests (W98+NAT), not higher than 1455. mtu 1455 mru 1455 #default-mru # And according to mturoute.exe, my max is 1424 (connection hangs # whenever I try -m > 1424). Note that the connexion never hangs if I # set mtu/mru to 1455 (but still fails with ICMP payload of 1424 or # more). # 1455 = 1500 - 24 - 20 (ip?) - 1? # whatever... # With a W2K behind Free, mturoute reports a max ICMP payload of 1372, # and a Path MTU of 1400 bytes. No disconnection to report whatever # the ppp MTU. # With a W98+QEMU+Free, mturoute reports a max ICMP payload of 1434, # and a Path MTU of 1462. No disconnection to report whatever # the ppp MTU.