Cisco TCP Connection Problem

[bigbadbond]

We have a CISCO 3640 software version 12.3 with a 16 port 16am analogue modem module. We have a scada system which connects to each of these modems via a telnet session to the port.
The problem we have occurs when there is a network failure/glitch between the scada server( remote site)or (local site) and the router. The telnet sessions are not dropped by the routers and when the scada system tries to connect back in it sees them as unavailable because the router still thinks it has connections. I have implemented a exec-timout 240 0 so it should restart and clear the lines every 4 hours. I dont think it can be done on idle data time as the modems are sometimes not used for long periods but the scada still needs a connection open to them incase. Any suggestions ??

 

[burtsbees]

VPN?

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[bigbadbond]

VPN ? Not sure what you mean by that? The scada opens multiple tcp telnet sessions to the modem ports, When the main router loses conection with the scada server it keeps these sessions open. When the server tries to connect back in it can't, until we kill all the lines or reboot the router.

No VPN's involved.

 

[burtsbees]

Remote----VPN TUNNEL----scada machines

My suggestion is a VPN. Unless you have local glitches all the time too, disconnecting you. At least with an IPSEC VPN (S2S), the tunnel will attempt to re-establish if a "glitch" takes it down...

What are these glitches, and how often do they occur?

 

[bigbadbond]

Thanks for the suggestion ! but as I said before it is nothing to do with or can be solved with by using a VPN. The server has multiple telnet seesions to multiple ports on the router " which is acting like a terminal server "
from a renote machine on another site. When the main link goes the router is not dropping the sessions. This also happens on a cisco dedicated terminal server's

 

[burtsbees]

The main link meaning the link from your site to their's or the link from the "terminal server" to the machines, or is that link the same? If it is the remote site-to-your site link, then how would a VPN NOT help???

If the local link flaps like that, there is no solution other than fixing THAT problem, rather than band-aid-ing the symptom...

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[bigbadbond]

Dont think you can blame the companies WAN infrastructure on this all wans suffer from outages due to weather stroms etc etc. It's just the fact that if a cisco has telnet sessions connected to the access server be it modem or serial and the netwrok is lost ? The Cisco will not clearm those sessions unless you clear the lines or do a re-load. Had no answer from Cisco's forums either ??

 

[burtsbees]

You can KRON the router to clear the sessions and reload...otherwise, it totally (or IF it totally) relies on an unstable WAN, so there is no other way other than to schedule the router to reload/clear the lines, and at the same time, schedule the devices to re-esatblish like 10 seconds later (assuming all devices are synched).

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tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!