Telnet connection over the internet drops after idle
Posted on 2006-11-05
I am having a lot of trouble with Telnet sessions over the internet. After 20 minutes of idle time the connection is often dropped. This is a major problem because of lost data entry productivity for many users. The users are at several locations with a PIX vpn to corporate. All are vpn over DSL. Previously this happened occasionally, now it happens very frequently. Now users at 3 of the 4 branch locations are dropping several times a day, it happens after 20 min. or so of idle time.
I have tried doing some diagnostics, testing, research, etc.
Telnet connections are very reliable on a LAN or a decent point-to-point WAN (such as fractional T1), idle time is not a problem, connections will stay for 2+ hours at least. The internet connections are un-predictable - anywhere from 20 min. to 2.5 hours of idle time will cause a disconnect. It is variable, some times the connection will drop 3 times in a row after 30 min. idle, then it will stay connected 3 times in a row with 30 min. idle. The testing was done over the internet with and without vpn involvement with no noticeable difference - frequent and un-predictable drops after 30+ min. of idle time with variable patterns. Pinging test with 10,000 cycles showed no relation to the drops, pings were 99% successful with occasional slow times but a decent average (times varied from 40ms to 1400ms with an average of about 70ms). Packet tracing did not show anything significant (not to me anyway) except:
after a certain amount of idle time a keystroke (usually the letter "c" but anything causes the same result) from the client causes a RST from the server. Then the client is disconnected from the session. netstat shows the session is gone on the client but netstat on the server shows the connection "established".
I have duplicated these results consistently on several LANS using different DSL providers for both client and server, with and without vpn's, using different Telnet client software and different server software.
Any suggestions would be appreciated.