IPsec tunnel blocks after a while without error. Where to find details?

There is an IPsec Tunnel created with OpenSwan that works perfectly well packets going through answers received etc until at some point in time traffic stops. I can regenerate the tunnel doing ipsec auto --down tunnelName ipsec auto --up tunnelName But eventually it will collapse again, sometimes after hours sometimes after days. I am not able to find any error messages for example in pluto.log that indicate that the tunnel collapsed, the last lines found are the ones reporting Quick_Mode entry. Our side: Ubuntu 14.04.4 LTS, Linux Openswan U2.6.38/K3.13.0-91-generic (netkey) Other side: SAP Router and unknown firewall I tapped this using tcpdump while the tunnel was not doing its job: 10:30:53.357186 IP us.isakmp > them.isakmp: isakmp: phase 1 I ident 10:30:53.384168 IP them.isakmp > us.isakmp: isakmp: phase 1 R ident 10:30:53.384880 IP us.isakmp > them.isakmp: isakmp: phase 1 I ident 10:30:53.425034 IP them.isakmp > us.isakmp: isakmp: phase 1 R ident 10:30:53.425770 IP us.isakmp > them.isakmp: isakmp: phase 1 I ident[E] 10:30:53.451727 IP them.isakmp > us.isakmp: isakmp: phase 1 R ident[E] 10:32:01.089957 IP us > them: ESP(spi=0x6e51327d,seq=0x14b), length 100 10:32:02.089097 IP us > them: ESP(spi=0x6e51327d,seq=0x14c), length 100 First part seems to be a succesful tunnel rekey negotiation second part two failing requests, or not? Netstat says that requests sent into the tunnel reach nothing more than SYN_SENT and then time out. Are there any other logs I could search as I am not allowed to debug the other end of the tunnel?