错误信息如下：
xl2tpd[2038]: Calling on tunnel 40109 xl2tpd[2038]: Call established with 192.168.33.1, Local: 28214, Remote: 1, Serial: 10 (ref=0/0) xl2tpd[2038]: start_pppd: I'm running: xl2tpd[2038]: "/bin/xl2tpcltpppd" xl2tpd[2038]: "passive" xl2tpd[2038]: "nodetach" xl2tpd[2038]: ":" xl2tpd[2038]: "auth" xl2tpd[2038]: "name" xl2tpd[2038]: "xl2tpdClient" xl2tpd[2038]: "file" xl2tpd[2038]: "/etc/xl2tp/xl2tpdcli.option" xl2tpd[2038]: "plugin" xl2tpd[2038]: "pppol2tp.so" xl2tpd[2038]: "pppol2tp" xl2tpd[2038]: "10" xl2tpd[2038]: result_code_avp: avp is incorrect size. 8 < 10 xl2tpd[2038]: handle_avps: Bad exit status handling attribute 1 (Result Code) on mandatory packet. xl2tpd[2038]: call_close: Call 28214 to 192.168.33.1 disconnected xl2tpd[2038]: result_code_avp: avp is incorrect size. 8 < 10 xl2tpd[2038]: handle_avps: Bad exit status handling attribute 1 (Result Code) on mandatory packet. xl2tpd[2038]: Terminating pppd: sending TERM signal to pid 2426 xl2tpd[2038]: Connection 1089 closed to 192.168.33.1, port 1701 (Result Code: expected at least 10, got 8)
根据网上找了下，以及自己最后解决发现，上面的日志其实看不出啥
我看ROS服务器端的打印是Encryption negotiation rejected
抓包看：
客户端先reject了服务器的MPPE加密协商
最后服务器终止了连接，里面的数据也是写得加密协商被拒绝
修改：
有两种方法
（1）去掉l2tp服务器端的加密必选项
（2）在l2tp的客户端加上+mppe-128
