I have a problem with telnet dropping after 20 minutes of idle time to a vendor's mainframe. The users will let the telnet connection stay open (idle) for 20 minutes. Right at the 20 min point the Telnet session drops.
There is a point to point T1 from our router to their managed router. So basically the workstation goes to a switch, hits the default gateway, through the firewall to the router where it travels across the T1 to their managed router and on to their mainframe.
Here are the details:
• Users are using telnet via Rumba, etc
• The telnet apps have a keep alive set
• Windows XP workstations has had a registry changed to allow idle times of up to 2 hours
• Windows Firewall on the workstations are disabled
• There is only 1 router with access lists and telnet is not restricted
• The firewall shows the connection as NOT being blocked
• Called another vendor (expert) on our firewall, same results after they tested (not blocked)
• Reduced hops from that bld to comm room from 4 to 2
• Network was replaced with 1 GBPS switches with a 1 GBPS uplink (fiber) to the comm room
The only setting in the firewall that can potentially disconnect an idle telnet session after 10 minutes is an aggressive aging timer placed on the telnet protocol that marks a connection for deletion after 10 minutes of idle time. If the firewall has exceeded its memory or connection threshold it will drop those connections marked for deletion. Our firewall has been operating well under its thresholds.
So what can I be missing? I am hoping this is something so simple stupid that I have overlooked looking for more complex causes.