Initially we had a site to site VPN working between sites for years (one site DSL, the other Cable), and suddenly it will not stay connected for more than a few days. The log shows an error saying phase 1 timed out because the remote site failed to respond. If I click connect on the IPsec Connection Status page it never reconnects. However if I restart one of the routers or delete the VPN configuration on both routers and recreate it, then it will connect.
I have tried updating firmware on both devices, I have tried adjusting MTU, I have tried disabling various attack prevention options, tried various different encryptions and nothing works. Eventually it tries to renegotiate the connection and fails because it says it doesn't receive a response even though both sites and devices are pingable and working.
Anybody have tips for how to fix this or what might be causing this?
