I have several site-to-site VPNs created with an ASA5520 at my office with Cisco 871s in the field. The remote sites connect through the VPN for email and connecting to a UNIX box using a terminal emulator. In many instances, these IPSEC tunnels terminate at the remote sites across a T1 internet circuit.
Users in the remote sites will lose connectivity to the unix box a few times a day but the VPN remains solid because not all users are kicked off. Only random users and usually those who walk away from their PC to get a product in the warehouse for the customer.
Cisco has had me add a sysopt connection tcpmss command on the ASA and appropriate commands on the routers. However, this did not resolve my issues.
Again, these are IPSEC tunnels and this problem only occurs in some locations. Other locations, with the same VPN configuration, have no problems. It appears to be an issue with certain ISPs only.
Any help would be appreciated. Thanks.