I have a site to site VPN between an ASA5520 and a PIX515E.
Recently, this VPN has started to drop. This is seemingly at random intervals, but it is always during the evening/night - never during the working day.
The tunnel drops for anywhere between 15-40 minutes before coming back up again with no config changes having been made.
While the VPN is down I am still able to access both the ASA and the PIX using the remote VPN client, as well as non-vpn accessible resources (i.e. websites) behind both devices.
I have some syslog captures from both ends during the issue. The entries specific to the VPN are detailed in the attached file (the trap logging is set to Error). VPN-Issue.txt