Operating System - Linux
1748209 Members
2788 Online
108759 Solutions
New Discussion

Re: Telnet Sessions Suddenly Lost

 
mosaix
Visitor

Telnet Sessions Suddenly Lost

Hello

 

I have the following setup

 

1 Hp Small Business Server

 

1 Hp server running sco

 

Approx 30 PC's

 

8 printers


All connected via a 10gb network

 

This setup has been runnig without problems for 6 years

 

The PCs connect to the sco server using telnet/TUN

 

For the last month two or three times a day the PCs lose connection to the sco server with the message 'connection closed by foreign host'.  Access to the Small Business Server is unaffected.

 

Sometimes one or two lose connection, sometimes all of them. The applications on the sco server continue to run and have to be killed off manually.

 

Any ideas?

 

Thanks in antcipation.

 

Mosaix

 

 

P.S. This thread has been moved from HP-UX > System Administration to Linux > networking - Hp Forum moderator

5 REPLIES 5
Dennis Handly
Acclaimed Contributor

Re: Telnet sessions suddenly lost

What HP-UX version are you using?

mosaix
Visitor

Re: Telnet sessions suddenly lost

Hi

 

Thanks for replying.

 

The Small Business Server is Windows based. The Unix server is running SCO rather than HP-UX.

 

Mosaix

Matti_Kurkela
Honored Contributor

Re: Telnet Sessions Suddenly Lost

> For the last month two or three times a day the PCs lose connection to the sco server with the message 'connection closed by foreign host'.  Access to the Small Business Server is unaffected.

 

So, for the client PCs, it looks like the SCO server is closing the connections.

 

Are there any log messages on the SCO server when a connection is lost?

 

If the SCO server logs say that the client is closing or resetting the connection, then there might be a firewall or a NAT device between the server and the clients. Such devices often maintain a table of existing connections. To protect against various types of attack, existing connections are allowed through only if a matching connection entry already exists in the table. When a new connection is established in the proper way, a new entry is added.

 

Because the resources of the firewall/NAT device are not infinite, those devices need to clean out old entries from their connection table. Sometimes this clean-up can be a bit overzealous. For example, if no data has transferred over a particular connection in a certain number of minutes, the connection may be cleaned up. At that point, both ends of the connection will see it as the opposite end closing the connection, while it is actually the firewall/NAT box that does the closing.

 

If many connections are lost at once, it might be that the firewall/NAT device is crashing and rebooting, or it is being reconfigured and needs to flush its connection table.

MK
mosaix
Visitor

Re: Telnet Sessions Suddenly Lost

Matti

 

Many thanks for your reply. I will investigate your suggestion and report back.

 

Many thanks.

 

Mosaix

 

mosaix
Visitor

Re: Telnet Sessions Suddenly Lost

Matti (and anyone else who gave this any thought) many thanks.

 

Problem solved.

 

I keep a diary of any significant events in the system (software upgrades, new hardware etc) and I'd gone back through this to the day the problems started without any luck.

 

Yesterday was the worst day of all, the HP SCO server was off the network for 6 hours resulting in considerable loss of business.

 

In the end I rebooted it. I started a ping on another system to show me when it had come up but, to my surprise, the ping responded immediately. There was insufficient time for the system to have rebooted. There was another device on the network with the same IP address!

 

Afetr much investigation another department had installed a remote system at another site and the suppliers had given it a fixed IP address - the same as the SCO server. These suppliers were the same ones who had refused to help with the problem!

 

Anyway thought I'd post this here to help anyone else with a similar problem in the future.

 

Again many thanks.

 

Mosaix