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I installed on pptp in my server.

when i set mss is 1356, the packets will be lost 20% - 30%

  /sbin/iptables -I FORWARD -p tcp --syn -i ppp+ -j TCPMSS --set-mss 1356

when i set mss is 1186, the packets will be almost no lost

who can tell me the reason ? thanks!

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what kind of network are you plugging in to? PPTP shouldn't need an MSS that low unless you're going through something that has an MTU far lower than Ethernet's 1500 bytes. –  Alnitak Nov 15 '11 at 14:42
--------------------------------PPP –  larry Nov 16 '11 at 1:02
so what's the MTU on your PPP link before you run PPTP on top of it? –  Alnitak Nov 16 '11 at 1:39

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