I found these lines in trac.log on client:
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[ 97 771][15 Nov 12:47:26][tunnel] [WARNING] [IkeTunnel::SendTunnelTestPkt(s)] no reply from the gw. Sending tunnel test pakcet
[ 97 771][15 Nov 12:47:26][tunnel] IkeTunnel::SendTunnelTestPktImpl: using sport 18005.
[ 97 771][15 Nov 12:47:26][tunnel] IkeTunnel::SendTunnelTestPktImpl: sending tunnel test packet from 172.30.100.102 to 10.x.x.x
...
[ 97 771][15 Nov 12:47:26][tunnel] [INFO] [IkeTunnel::ReceivedEsp] (0x0x6579d20): Received Esp Packet from gw 10.x.x.x .Must be tunnel test packet
[ 97 771][15 Nov 12:47:26][tunnel] IPsecTunnel::ReceiveTunnelTestPkt: started
[ 97 771][15 Nov 12:47:26][tunnel] IPsecTunnel::ReceiveTunnelTestPkt: Received tunnel test reply
[ 97 771][15 Nov 12:47:26][tunnel] [INFO] [IkeTunnel::ReceivedEsp] (0x0x6579d20): Tunnel state is connected
...
[ 97 771][15 Nov 12:47:28][tunnel] [WARNING] [IkeTunnel::SendTunnelTestPkt(s)] receive reply from the gw. Descheduling TunnelTestTimeout and scheduling CheckDGDTimeStamp again
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[ 97 771][15 Nov 12:47:28][tunnel] [INFO] [IkeTunnel::CheckDGDTimeStamp(s)] timeout is not reached yet. Scheduling next DGD query in 17977 ms.
...
[ 97 771][15 Nov 12:47:46][tunnel] [COVERAGE] [IkeTunnel::CheckDGDTimeStamp(s)] __start__
[ 97 771][15 Nov 12:47:46][tunnel] [INFO] [IkeTunnel::CheckDGDTimeStamp(s)] tunnel 0x0x6579d20
[ 97 771][15 Nov 12:47:46][tunnel] IkeTunnel::CheckDGDTimeStamp: current timestamp = I64d and DGD timestamp = I64d
[ 97 771][15 Nov 12:47:46][tunnel] [INFO] [IkeTunnel::CheckDGDTimeStamp(s)] timeout reached. Scheduling tunnel test every 2000 ms until 20000.
[ 97 771][15 Nov 12:47:46][tunnel] [COVERAGE] [IkeTunnel::CheckDGDTimeStamp(s)] __end__ Total:0 milliseconds.
[ 97 771][15 Nov 12:47:46][tunnel] [COVERAGE] [IkeTunnel::SendTunnelTestPkt(s)] __start__
[ 97 771][15 Nov 12:47:46][tunnel] [INFO] [IkeTunnel::SendTunnelTestPkt(s)] tunnel 0x0x6579d20
[ 97 771][15 Nov 12:47:46][tunnel] [WARNING] [IkeTunnel::SendTunnelTestPkt(s)] no reply from the gw. Sending tunnel test pakcet
[ 97 771][15 Nov 12:47:46][tunnel] IkeTunnel::SendTunnelTestPktImpl: using sport 18006.
[ 97 771][15 Nov 12:47:46][tunnel] IkeTunnel::SendTunnelTestPktImpl: sending tunnel test packet from 172.30.100.102 to 10.x.x.x.
[ 97 771][15 Nov 12:47:46][tunnel] [COVERAGE] [IkeTunnel::SendPacket] (0x0x6579d20): __start__
[ 97 771][15 Nov 12:47:46][tunnel] IPsecTunnel::SendPacket: sending esp packet
...
[ 97 771][15 Nov 12:47:48][tunnel] [WARNING] [IkeTunnel::SendTunnelTestPkt(s)] no reply from the gw. Sending tunnel test pakcet
[ 97 771][15 Nov 12:47:48][tunnel] IkeTunnel::SendTunnelTestPktImpl: using sport 18007.
[ 97 771][15 Nov 12:47:48][tunnel] IkeTunnel::SendTunnelTestPktImpl: sending tunnel test packet from 172.30.100.102 to 10.x.x.x.
[ 97 771][15 Nov 12:47:48][tunnel] [COVERAGE] [IkeTunnel::SendPacket] (0x0x6579d20): __start__
[ 97 771][15 Nov 12:47:48][tunnel] IPsecTunnel::SendPacket: sending esp packet
...
x10 times
...
[ 97 771][15 Nov 12:48:04][tunnel] [COVERAGE] [IkeTunnel::SendPacket] (0x0x6579d20): __end__ Total:0 milliseconds.
[ 97 771][15 Nov 12:48:04][tunnel] [COVERAGE] [IkeTunnel::SendTunnelTestPkt(s)] __end__ Total:0 milliseconds.
[ 97 771][15 Nov 12:48:06][tunnel] IkeTunnel::TunnelTestTimeout: stop sending tunnel tests packets. deschedule SendTunnelTestPkt
[ 97 771][15 Nov 12:48:06][tunnel] IkeTunnel::TunnelTestTimeout:Tunnel is disconnected !!!!