VPN sobre IPsec desconecta após 30 segundos

Question

Estou tentando conectar-me ao VPN através do IPSec no Ubuntu 14.04. Estou configurando por meio do applet:

TudofuncionaepossomeconectaràVPN.Noentanto,após30segundos,elesempredesconecta.Ologé:

Sep2121:16:52.638xl2tpd[3778]:Connectingtohostsome.domain.com,port1701Sep2121:16:52.653xl2tpd[3778]:Connectionestablishedtoxx.xxx.xxx.xxx,1701.Local:9798,Remote:61236(ref=0/0).Sep2121:16:52.654xl2tpd[3778]:Callingontunnel9798Sep2121:16:52.673xl2tpd[3778]:Callestablishedwithxx.xxx.xxx.xxx,Local:30953,Remote:59837,Serial:1(ref=0/0)Sep2121:16:52.679xl2tpd[3778]:start_pppd:I'mrunning:Sep2121:16:52.680xl2tpd[3778]:"/usr/sbin/pppd" 
Sep 21 21:16:52.681 xl2tpd[3778]: "passive" 
Sep 21 21:16:52.681 xl2tpd[3778]: "nodetach" 
Sep 21 21:16:52.682 xl2tpd[3778]: ":" 
Sep 21 21:16:52.682 xl2tpd[3778]: "file" 
Sep 21 21:16:52.682 xl2tpd[3778]: "/etc/ppp/VPN.options.xl2tpd" 
Sep 21 21:16:52.683 xl2tpd[3778]: "/dev/pts/3" 
Sep 21 21:16:52.701 pppd[3837]: Plugin passprompt.so loaded.
Sep 21 21:16:52.701 pppd[3837]: pppd 2.4.5 started by root, uid 0
Sep 21 21:16:52.702 pppd[3837]: Using interface ppp0
Sep 21 21:16:52.702 pppd[3837]: Connect: ppp0 <--> /dev/pts/3
Sep 21 21:16:52.757 pppd[3837]: CHAP authentication succeeded
Sep 21 21:16:52.815 pppd[3837]: local  IP address xxx.xxxx.xx.xxx
Sep 21 21:16:52.818 pppd[3837]: remote IP address xxx.xxx.xx.xxx
Sep 21 21:17:41.580 Stopping xl2tpd: xl2tpd.
Sep 21 21:17:41.580 xl2tpd[3778]: death_handler: Fatal signal 15 received
Sep 21 21:17:41.580 pppd[3837]: Modem hangup
Sep 21 21:17:41.584 pppd[3837]: Connect time 0.9 minutes.
Sep 21 21:17:41.584 pppd[3837]: Sent 400 bytes, received 164 bytes.
Sep 21 21:17:41.585 pppd[3837]: Connection terminated.
Sep 21 21:17:41.602 ipsec_setup: Stopping Openswan IPsec...
Sep 21 21:17:41.623 pppd[3837]: Exit.

Eu já experimentei uma máquina Linux e uma máquina Ubuntu, e isso acontece toda vez. O que poderia ser?