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тАО03-05-2009 10:51 AM
тАО03-05-2009 10:51 AM
Subsequently, it is necessary for them to undock, automatically switching them to Wireless, and dropping their telnet sessions as a new IP is acquired.
When they attempt to reconnect, the connection fails because
Username: baxterd
Password:
You are at maximum allowed processes for your user name
(This is a company-wide restriction (to 2 sessions per node) to stop licenses being locked up in idle sessions)
The salient point however is that, although undocking caused the telnet sessions to terminate, the VMS processes did/do not hangup, therefore requiring intervention by an admin to remove them.
Is there a System Parameter or TCPIP Sysconfig parameter that can be set to cause these sessions to hang up when the Telnet session terminates???
I know that Virtual Terminals are generally an option, however there have been bad experiences (before my time) here, which takes them off the table, at least for the time being. I will be more than happy to listen to conversations about Virtual Terminals, however I would really like to concentrate on alternative methods of fixing the problem, if there are any.
Thanks
Dave.
Solved! Go to Solution.
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тАО03-05-2009 01:11 PM
тАО03-05-2009 01:11 PM
Re: VMS processes left hanging
Unless VMS' TCP stack is notified that the other end has disconnected it can't do anything - and evidently this is not occurring. Keepalives are a common method for controlling this but unfortunately Reflection (and many other emulators as well) does not support them directly though I think that you can modify something in the Windows registry to enable/control them.
> I would really like to concentrate on alternative methods of fixing the problem
Perhaps a workaround rather than a cure?
Have you considered possibly writing a bit of code - could even be DCL - that would run detached and perhaps PING your terminals' source addresses on some regular cycle and if not responsive take whatever remedial steps your admins currently do to terminate them?
Or perhaps you could have your SYLOGIN determine the maximum number of terminal sesssions the user was permitted, and, if they were exceeding, that offer them the opportunity to terminate one (or more)?
I suspect that there are numerous other ways to deal with this as well. You didn't say what state you find the processes in when the terminal has been disconnected nor how you terminate them. I presume that VMS is fat, dumb, and happy with a process in LEF or HIB and you need only STOP/ID or perhaps issue some database termination command?
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тАО03-05-2009 01:46 PM
тАО03-05-2009 01:46 PM
Re: VMS processes left hanging
What I don't understand is that we just migrated from Alpha to Itanium and changed stack from TCPWare to TCPIP Services.
Since the migration, this issue has arisen, and also a related issue where Telnet sessions appear to timeout after ~2 hours. This normally happens if the sessions are idle, however they don't have to be (although I have not seen one drop while actually entering commands). It is possible that the "timeout" issue is firewall-related.
To return to the initial problem. I will look into your suggestion of setting up a detached process to watch for dropped sessions, however this seems to be a very risky approach, i.e. could kill an important process.
Dave.
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тАО03-05-2009 01:52 PM
тАО03-05-2009 01:52 PM
Re: VMS processes left hanging
I'd bet on it. Leave a telnet session logged in and idle that does not have its connection pass through the firewall and see what happens.
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тАО03-05-2009 01:57 PM
тАО03-05-2009 01:57 PM
Re: VMS processes left hanging
It is possible that the act of PINGing the source of a disconnected telnet session will clue the TCP stack in to the fact that the remote end is gone and drop the telnet session. You might just experiment with PING and wait and see if after a short time - or maybe even immediately - the telnet session drops. You might also try broadcasting something to the session that you suspect is gone. Or maybe use the SHARE privilege to open a channel to it and write something, anything, like a nul character perhaps and that might cause the session to drop.
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тАО03-05-2009 01:59 PM
тАО03-05-2009 01:59 PM
Re: VMS processes left hanging
Is this related to your earlier ....
http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=1317706
The use of telnet-based virtual terminals and keepalive settings does look applicable here.
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тАО03-05-2009 03:30 PM
тАО03-05-2009 03:30 PM
Re: VMS processes left hanging
Anyway, maybe you can have your SYLOGIN attempt to contact any connections already owned by someone logging in interactively and if they appear not viable let the user decide whether or not to terminate them. Or maybe just probing them will result in the stack terminating them for you.
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тАО03-05-2009 03:33 PM
тАО03-05-2009 03:33 PM
Re: VMS processes left hanging
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тАО03-06-2009 03:43 AM
тАО03-06-2009 03:43 AM
Re: VMS processes left hanging
While I agree that VT might be the most appropriate way to go, I am struggling with the problem "This didn't happen before the cutover, and we weren't using VT's then"
I guess my attitude is that we shouldn't have to go that route to stop something that wasn't happening before.
At the moment, I am looking at the settings of
tcp_keepalive_default = 0
tcp_keepcnt = 8
tcp_keepidle = 14400
tcp_keepinit = 150
tcp_keepintvl = 150
in sysconfig. These values are the defaults. In particular, "tcp_keepalive_default = 0" (turned off ???)
would you have any recommendations for appropriate values??
Dave
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тАО03-06-2009 04:46 AM
тАО03-06-2009 04:46 AM
Re: VMS processes left hanging
When turning this knob one has to weigh the possibility of terminating a valid process against discovery of no longer viable connections in a timely manner. How quickly do you need to discover that a process has been disconnected? Keepalives are generally not used for rapid response situations. I would expect that your current values, if enabled, are interpretted thusly
tcp_keepidle = 14400
tcp_keepintvl = 150
tcp_keepcnt = 8
After 14400 half seconds (2 hours) of idleness, begin sending keepalive polls every 150 half seconds (75 seconds) as many as 8 times hoping to get a response (times are in 500 millisecond or half second units). If this total time passes without a response back then terminate the connection. With this config it would take 2:10 minutes of idle time before a session would drop.
I suspect that tcp_keepalive_default = 0 does indicate that keepalives are "off". That is the default behaviour from most stacks. It is usually enable on an application by application basis - in this instance "telnet".
I do think that enabling keepalives for telnet will help you with catching and terminating disconnected sessions. But, you need to consider the reliablility of your network when lowering these values or risk terminating viable telnet connections. You don't want a short network hiccup to result in all telnet sessions being terminated because they couldn't respond during a too short keepalive idle+intervals duration. If you're trying to catch a disconnect immediately in order to permit a user to disconnect from their docking station and immediately re-connect then this probably isn't the right tool. You want to be fairly conservative in configuring it and be considerate of the health of the networks that your telnet users traverse.