启动后立即失败，系统日志：
pr 6 15:37:08 dmitry-ci pppd[5677]: Plugin pppol2tp.so loaded.
Apr 6 15:37:08 dmitry-ci pppd[5677]: Plugin /usr/lib/pppd/2.4.7/nm-l2tp-pppd-plugin.so loaded.
Apr 6 15:37:08 dmitry-ci pppd[5677]: pppd 2.4.7 started by root, uid 0
Apr 6 15:37:08 dmitry-ci pppd[5677]: Using interface ppp0
Apr 6 15:37:08 dmitry-ci pppd[5677]: Connect: ppp0 <-->
Apr 6 15:37:08 dmitry-ci pppd[5677]: Overriding mtu 1500 to 1400
Apr 6 15:37:08 dmitry-ci pppd[5677]: Overriding mru 1500 to mtu value 1400
Apr 6 15:37:08 dmitry-ci NetworkManager[1052]: <info> [1617716228.7363] manager: (ppp0): new Ppp device (/org/freedesktop/NetworkManager/Devices/15)
Apr 6 15:37:08 dmitry-ci systemd-udevd[5680]: ethtool: autonegotiation is unset or enabled, the speed and duplex are not writable.
Apr 6 15:37:08 dmitry-ci pppd[5677]: Overriding mtu 1500 to 1400
Apr 6 15:37:08 dmitry-ci pppd[5677]: EAP: Identity prompt "Name"
Apr 6 15:37:08 dmitry-ci pppd[5677]: EAP: peer reports authentication failure
Apr 6 15:37:08 dmitry-ci pppd[5677]: Overriding mtu 1500 to 1400
Apr 6 15:37:08 dmitry-ci pppd[5677]: Overriding mru 1500 to mtu value 1400
Apr 6 15:37:08 dmitry-ci pppd[5677]: Connection terminated.
Apr 6 15:37:08 dmitry-ci charon: 07[KNL] interface ppp0 deleted
Apr 6 15:37:08 dmitry-ci NetworkManager[5676]: xl2tpd[5676]: death_handler: Fatal signal 15 received
Apr 6 15:37:08 dmitry-ci NetworkManager[5676]: xl2tpd[5676]: Terminating pppd: sending TERM signal to pid 5677
Apr 6 15:37:08 dmitry-ci NetworkManager[5676]: xl2tpd[5676]: Connection 28157 closed
按照本指南进行设置：https ://www.tecmint.com/setup-l2tp-ipsec-vpn-client-in-linux/
有任何想法吗？请帮忙！在两台不同的电脑上试过，结果是一样的。凭证可以 100%。