Sometimes network congestion and latency cause the UDP protocol, most commonly used with OpenVPN, to drop packets and even lose the connection. You will see a ‘Replay window backtrack occurred’ error in the log if this is occurring. One solution is to switch to the TCP protocol, assuming your server is configured to support a TCP connection.
在使用UDP协议的时候，如果网络不稳定，偶尔会出现丢包问题，或者分包错误，导致链接中断，
解决方法有两种，
一是修改 TCP 方式
[root@aikaiyuan ~]# cat /etc/openvpn/server.conf | grep proto
proto tcp
[root@aikaiyuan ~]#
二是修改MTU
添加 link-mtu 1400 参数
或者直接修改sys 配置
echo 1400 > /sys/class/net/tap0/mtu
echo 1400 > /sys/class/net/eth0/mtu
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