我已经安装，l2tp-ipsec-vpn但是当我尝试连接到 vpn 服务器时出现错误 500。
以下是日志：
Jun 17 12:54:37.449 ipsec_setup: Stopping Openswan IPsec...
Jun 17 12:54:38.858 Stopping xl2tpd: xl2tpd.
Jun 17 12:54:38.859 xl2tpd[1511]: death_handler: Fatal signal 15 received
Jun 17 12:54:38.872 ipsec_setup: Starting Openswan IPsec U2.6.37/K3.2.0-23-generic...
Jun 17 12:54:39.027 ipsec__plutorun: Starting Pluto subsystem...
Jun 17 12:54:39.033 ipsec__plutorun: adjusting ipsec.d to /etc/ipsec.d
Jun 17 12:54:39.037 recvref[30]: Protocol not available
Jun 17 12:54:39.038 xl2tpd[2442]: This binary does not support kernel L2TP.
Jun 17 12:54:39.038 xl2tpd[2444]: xl2tpd version xl2tpd-1.3.1 started on atp-ThinkPad-SL410 PID:2444
Jun 17 12:54:39.038 xl2tpd[2444]: Written by Mark Spencer, Copyright (C) 1998, Adtran, Inc.
Jun 17 12:54:39.038 xl2tpd[2444]: Forked by Scott Balmos and David Stipp, (C) 2001
Jun 17 12:54:39.038 xl2tpd[2444]: Inherited by Jeff McAdams, (C) 2002
Jun 17 12:54:39.039 xl2tpd[2444]: Forked again by Xelerance (www.xelerance.com) (C) 2006
Jun 17 12:54:39.039 xl2tpd[2444]: Listening on IP address 0.0.0.0, port 1701
Jun 17 12:54:39.040 Starting xl2tpd: xl2tpd.
Jun 17 12:54:39.062 ipsec__plutorun: 002 added connection description "L2TP"
Jun 17 12:55:30.753 104 "L2TP" #1: STATE_MAIN_I1: initiate
Jun 17 12:55:30.754 010 "L2TP" #1: STATE_MAIN_I1: retransmission; will wait 20s for response
Jun 17 12:55:30.754 010 "L2TP" #1: STATE_MAIN_I1: retransmission; will wait 40s for response
Jun 17 12:55:30.754 003 "L2TP" #1: ignoring Vendor ID payload [MS NT5 ISAKMPOAKLEY 00000008]
Jun 17 12:55:30.754 003 "L2TP" #1: received Vendor ID payload [RFC 3947] method set to=109
Jun 17 12:55:30.754 003 "L2TP" #1: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-02_n] meth=106, but already using method 109
Jun 17 12:55:30.755 003 "L2TP" #1: ignoring Vendor ID payload [FRAGMENTATION]
Jun 17 12:55:30.755 003 "L2TP" #1: ignoring Vendor ID payload [MS-Negotiation Discovery Capable]
Jun 17 12:55:30.755 003 "L2TP" #1: ignoring Vendor ID payload [IKE CGA version 1]
Jun 17 12:55:30.755 106 "L2TP" #1: STATE_MAIN_I2: sent MI2, expecting MR2
Jun 17 12:55:30.755 010 "L2TP" #1: STATE_MAIN_I2: retransmission; will wait 20s for response
Jun 17 12:55:30.755 003 "L2TP" #1: NAT-Traversal: Result using RFC 3947 (NAT-Traversal): i am NATed
Jun 17 12:55:30.755 108 "L2TP" #1: STATE_MAIN_I3: sent MI3, expecting MR3
Jun 17 12:55:30.756 004 "L2TP" #1: STATE_MAIN_I4: ISAKMP SA established {auth=OAKLEY_PRESHARED_KEY cipher=oakley_3des_cbc_192 prf=oakley_sha group=modp1024}
Jun 17 12:55:30.756 117 "L2TP" #2: STATE_QUICK_I1: initiate
Jun 17 12:55:30.756 010 "L2TP" #2: STATE_QUICK_I1: retransmission; will wait 20s for response
Jun 17 12:55:30.756 003 "L2TP" #2: ignoring informational payload, type IPSEC_RESPONDER_LIFETIME msgid=6b03ff69
Jun 17 12:55:30.756 003 "L2TP" #2: NAT-Traversal: received 2 NAT-OA. ignored because peer is not NATed
Jun 17 12:55:30.756 003 "L2TP" #2: our client subnet returned doesn't match my proposal - us:192.168.1.3/32 vs them:109.162.174.235/32
Jun 17 12:55:30.757 003 "L2TP" #2: Allowing questionable proposal anyway [ALLOW_MICROSOFT_BAD_PROPOSAL]
Jun 17 12:55:30.757 004 "L2TP" #2: STATE_QUICK_I2: sent QI2, IPsec SA established transport mode {ESP=>0x23af21f8 <0xdb4a87b6 xfrm=AES_128-HMAC_SHA1 NATOA=none NATD=none DPD=none}
Jun 17 12:55:31.759 xl2tpd[2444]: Connecting to host x.x.x.x, port 1701
Jun 17 12:55:32.021 xl2tpd[2444]: Connection established to x.x.x.x, 1701. Local: 4720, Remote: 200 (ref=0/0).
Jun 17 12:55:32.023 xl2tpd[2444]: Calling on tunnel 4720
Jun 17 12:55:32.454 xl2tpd[2444]: Call established with x.x.x.x, Local: 9667, Remote: 3, Serial: 1 (ref=0/0)
Jun 17 12:55:32.456 xl2tpd[2444]: start_pppd: I'm running:
Jun 17 12:55:32.456 xl2tpd[2444]: "/usr/sbin/pppd"
Jun 17 12:55:32.457 xl2tpd[2444]: "passive"
Jun 17 12:55:32.458 xl2tpd[2444]: "nodetach"
Jun 17 12:55:32.458 xl2tpd[2444]: ":"
Jun 17 12:55:32.459 xl2tpd[2444]: "file"
Jun 17 12:55:32.459 xl2tpd[2444]: "/etc/ppp/L2TP.options.xl2tpd"
Jun 17 12:55:32.460 xl2tpd[2444]: "ipparam"
Jun 17 12:55:32.461 xl2tpd[2444]: "x.x.x.x"
Jun 17 12:55:32.462 xl2tpd[2444]: "/dev/pts/1"
Jun 17 12:55:32.583 pppd[2711]: Plugin passprompt.so loaded.
Jun 17 12:55:32.583 pppd[2711]: pppd 2.4.5 started by root, uid 0
Jun 17 12:55:32.619 pppd[2711]: Using interface ppp0
Jun 17 12:55:32.620 pppd[2711]: Connect: ppp0 <--> /dev/pts/1
Jun 17 12:55:33.693 pppd[2711]: /usr/bin/L2tpIPsecVpn exited with code 0
Jun 17 12:55:34.454 [ERROR 404] Authentication failed: closing connection to 'L2TP'
Jun 17 12:55:34.456 pppd[2711]: MS-CHAP authentication failed: E=691 Authentication failure
Jun 17 12:55:34.457 pppd[2711]: CHAP authentication failed
Jun 17 12:55:34.461 Stopping xl2tpd: xl2tpd.
Jun 17 12:55:34.462 xl2tpd[2444]: death_handler: Fatal signal 15 received
Jun 17 12:55:34.463 pppd[2711]: Modem hangup
Jun 17 12:55:34.463 pppd[2711]: Connection terminated.
Jun 17 12:55:34.474 ipsec_setup: Stopping Openswan IPsec...
Jun 17 12:55:34.482 pppd[2711]: Exit.
Jun 17 12:55:35.587 ipsec_setup: ERROR: Module xfrm4_mode_transport is in use
Jun 17 12:55:35.665 ipsec_setup: ERROR: Module esp4 is in use
我从 Ubuntu 11.10 开始就遇到了这个问题，尽管我可以轻松地从 Windows 连接到服务器。我使用的是 Ubuntu 12.0 64 位。
答案1
看起来您配置了错误的用户名或密码。
请参阅以下内容来为 pppd 启用更多调试信息： http://wiki.l2tpipsecvpn.tuxfamily.org/wiki/index.php?title=Main_Page#Diagnose_PPPD_problems