The MTU on PPTP causes some websites to not access or access is very slow

Continue with the previous post to talk about the MTU causing very slow access issues or direct access. Our server is Aliyun Singapore server, after the successful PPTP connection, access to the wall of most sites outside the basic no pressure, but can not put Baidu, it is strange, have access to the wall of Google, Baidu is also the wall of Singapore?

After some Baidu + Google, found that indeed a lot of people have such a situation. The MTU of the Ppp0 NIC interface below the Linux system is 1396, while the default MTU of our Windows client is 1496. Originally in the MTU at the time of routing communication will self-negotiation, but some operators or host management in order to prevent DDoS, disable the function of ping (do not know can play a role of anti-DDoS), MTU from negotiation just use the ICMP protocol to communicate, resulting in the inability to negotiate the MTU, Sent to the PPTP server packets, there will be problems, naturally some sites will not be able to access, some sites time-out situation.

Here are a few ways to resolve the Ppp0 interface MTU.

1. The MTU 1496 is configured on the PPTP server/etc/ppp/options.pptpd.

2. The MTU value is modified directly to the interface of the ppp0, and then the PPTP service is restarted to take effect.

  Ifconfig ppp0 MTU 1496   /etc/init.d/pptpd restart

Modifying the Iptables implementation

Iptables-a forward-p tcp-syn-s 192.168.100.0/24-j TCPMSS-SET-MSS 1496

Finally reconnect, you can access some of the problem because of the MTU is not unified, access to the site.

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The MTU on PPTP causes some websites to not access or access is very slow