I have found one strange problem with IPSec VPN, the scenario is like this, our corporate office is connected to its 25 remote office with IPSec VPN, at corporate site, cisco 2811 router is installed and same type of router is installed at each remote site and IPSec VPN is configured between remote office and corporate office and further each remote site router has two other VPN configured which are working properly. Now the problem is, 4 out of 25 remote offices are not getting up with corporate office, I mean the VPN is not getting up for these location. I sit at corporate office and have tried my level best to up these VPN but the problem not getting resolved.
Now the strange problem is that the VPN gets up by itself, after sometime like in 10days or 20days, for sometime and gets down by itself later.
Anyone who can give some insights where the problem could be and how could i troubleshoot the problem?
Thanks in advance for your valuable response