I am having a 2600 seires router.When i telnet to this router and do some debug like Debug isdn q921 after issuing terminal monitor command, after few minutes the output vanishes and i have to telnet againg to see the output.
Is the exec timeout timing out? The debug output traffic is not enough in its own to keep the telnet open. Whenever I am doing serious debugging, I do:
line vty 0 4
If you have a session timeout configured as well, you should kill that too.
Don't forget to put them back again when you have finished debugging.
No its not configured, but i cant see the debug output after few minutes and if I close the telnet window and telnet again then i can see the output.
The debug settings are global, i.e. they are not specific to that particular telnet session. That is why you can quit the telnet, start a new one, issue term mon, and re-connect to the debug. You would see the debug on the console too if that was connected.
If you cannot see anything for exec-timeout under the vty lines, then the exec-timeout is the default, which is 4 minutes if I remember right. You need to specify no exec-timeout explicitly - it will then appear in the show run.
However, there is a doubt forming in my mind .... are you saying that the debug output disappears but you still have exec control on the telnet session? If so, what if you then do show debug? Could someone else be logging in and disabling your debug?
Yes the debug output disappears but i have the control on telnet sessionn if do show debug it shows debugging is on moreover nobody is logged in at the point of time
So when you do show debug, it lists isdn q921, but you don't see any debug lines? That seems very strange. Could it be that there is simply nothing going on with q921 at the time?
Found something! I suspect it is similar to bug CSCds85771. This bug was reported on AS5300, but maybe it applies to other platforms. Which version of IOS are you running? Here is the description:
Customer does term mon, and enables some debug. For a while the debug output shows on his screen (also in the log), but after a random while for some reason the debug output does not show on the terminal anymore (still shows in the system log).
This problem can happen with any debug command.
The reference is:
So, if you log the debug to a syslog, does the syslog still show the debug?
no basically i debug Modem and debug ppp authen and i dial at the same time c can see the output of modem and ppp authencation but after some time i disconnect and connect again i can't see the output then i have to close the telnet window and relogin to the router the issue the ter moni and can see the output again
It might very well be a bug like Kevin suggested. Try enabling buffered logging if you do not have a syslog server. This can be done using the logging buffered command in the global configuration mode. See if the logs show up there and not on the terminal. If that is the case then it could be an instance of the bug Kevin has mentioned.