D-Link DFL-260E User Manual page 483

9.8.6. Specific Symptoms
Chapter 9. VPN
when there is something that fails in terms of network size on either local network or remote
network. Since NetDefendOS has determined that it is a type of network size problem, it will try one
last attempt to get the correct network by sending a config mode request.
By using ikesnoop when both sides initiate the tunnel, it should be simple to compare the network
that both sides are sending in phase-2. With that information it should be possible to spot the
network problem. It can be the case that it is a network size mismatch or that it does not match at all.
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