操作系统：ubuntu 14.04
我是是按照 http://blog.atime.me/note/l2tp_ipsec_installation_on_ubuntu.html 来配置的
ipsec verify 出现错误，google了好久也没找到解决方法。

 > root@l:~# ipsec verify Checking if IPsec got installed and started
> correctly:
> 
> Version check and ipsec on-path                         [OK] Openswan
> U2.6.42/K3.16.0-23-generic (netkey) See `ipsec --copyright' for
> copyright information. Checking for IPsec support in kernel           
> [OK]  NETKEY: Testing XFRM related proc values
>          ICMP default/send_redirects                    [OK]
>          ICMP default/accept_redirects                  [OK]
>          XFRM larval drop                               [OK] Hardware random device check                            [N/A] Checking
> rp_filter                                      [ENABLED] 
> /proc/sys/net/ipv4/conf/all/rp_filter                  [ENABLED] 
> /proc/sys/net/ipv4/conf/default/rp_filter              [ENABLED] 
> /proc/sys/net/ipv4/conf/eth0/rp_filter                 [ENABLED] 
> /proc/sys/net/ipv4/conf/lo/rp_filter                   [ENABLED]
> Checking that pluto is running                          [OK]  Pluto
> listening for IKE on udp 500                     [OK]  Pluto listening
> for IKE on tcp 500                     [NOT IMPLEMENTED]  Pluto
> listening for IKE/NAT-T on udp 4500              [OK]  Pluto listening
> for IKE/NAT-T on tcp 4500              [NOT IMPLEMENTED]  Pluto
> listening for IKE on tcp 10000 (cisco)           [NOT IMPLEMENTED]
> Checking NAT and MASQUERADEing                          [TEST
> INCOMPLETE] Checking 'ip' command                                  
> [OK] Checking 'iptables' command                             [OK]
> 
> ipsec verify: encountered errors

另外，vpn是可以连上的，也可以访问网络，但是过一会就会出现错误，然后就无法访问网络了

 > Nov  7 01:57:17 l pppd[14130]:   script /etc/ppp/ip-down, pid 14156
> Nov  7 01:57:17 l pppd[14130]: Terminating on signal 15 Nov  7
> 01:57:17 l pppd[14130]: sending SIGTERM to process 14156 Nov  7
> 01:57:17 l pppd[14130]: Exit. Nov  7 01:57:17 l xl2tpd[13898]:
> get_call: can't find call 48693 in tunnel 40624#012 (ref=0/0) Nov  7
> 01:57:21 l xl2tpd[13898]: message repeated 81 times: [ get_call: can't
> find call 48693 in tunnel 40624#012 (ref=0 /0)]

希望大家可以帮助我解决这个问题