Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

VTY Session Hangs when Changing VLAN on Port


SUP1A-2GE w/128mb

CatOS 8.3.5


(Using TACACS for login)

When attempting to change the VLAN on a port, the telnet session hangs after pressing enter. Able to log back in with new session. Same thing happens again.

a) What is causing this?

Secondary to this, when looking at CPU processes, util is 100% as a result of each vty session. Can't disconnect the sessions......error reports a command is executing. But will eventually time out after ~30 minutes or so.

b) How can those sessions be killed besides using the "disconnect" command?

Thanks for any assistance.


Re: VTY Session Hangs when Changing VLAN on Port

Danny, this is a strange annomaly.. are you certain that before changing vlan on a port the cpu is at normal and not at 100% , it seems this could be the case where cpu is at its max busy trying to recover from something else but telnet session thus causing telnet session timouts or hangs..

I would suggest to console to switch locally and see whats going on from console.

Anything in the logs indicating other issues?

you can kill telnet session by issuing

" disconnect IP_address "



New Member

Re: VTY Session Hangs when Changing VLAN on Port

Jorge....I am certain that cpu is normal prior to the command. I've also proved out a couple of other items:

1) Able to assign the same vlan to other ports with no problem.

2) Not able to assign a different vlan to this particular port.

Maybe it's isolated to a specific port problem. The disconnect command only allows me to enter the session id (e.g. 1, 2, 3, etc.). Not by ip address.

Logging in through the console results in the same issue and the processes now show that session as being the high util culprit. So, it's not respective of only telnet. Nothing else shows in the logs.

Additionally, I just noticed that if I let the hung session sit, it will finally complete and the vlan does change on the port. However, it took at least 30 minutes to complete.

Re: VTY Session Hangs when Changing VLAN on Port

Danny.. can you retreave diagnostics from this module, you should have the option to do " show test mod# " to see line card diag status and its ports.

also rule out any other config on this particular port that may not be seen and be configure for something else such as in etherchannel or trunk config " set port host mod/Port# " not that I have seen similar issues but to have a clean port in terms of config.

lastly look into your current catos code if there are bugs causing this annomally, but from what you have discribed it could be problem with the port/card.

New Member

Re: VTY Session Hangs when Changing VLAN on Port

Thanks for the responses Jorge. The "show test" command shows all ports as passed. However, I would be interested to see if they all pass after a reset since this switch has been up for quite some time now. I will prob try this early a.m. tomorrow.

The config is clear as you suggested. However, another curiosity I just noticed is the listed MAC address. The actual MAC of my adapter ends with 4d-50. That is shown as the Last-Src-Addr but the Secure-Src-Addr indicates 4d-51. Not sure if this relates but I'm not sure why it reflects that either. The same device has been plugged into this port and has never changed. Port Security is disabled as well. Output below....

Port Flooding on Address Limit Last-Src-Addr Vlan

----- ------------------------- ----------------- ----

4/32 Enabled 00-12-3f-1f-4d-50 54

Port Num-Addr Secure-Src-Addr Vlan Age-Left Shutdown/Time-Left

----- -------- ----------------- ---- -------- ------------------

4/32 1 00-12-3f-1f-4d-51 * 112 - - -

Re: VTY Session Hangs when Changing VLAN on Port

interesting, if you connect that system to a different port on that same module or other module does the samething happens with high cpu if it does you may have isolated the issue being that system.

New Member

Re: VTY Session Hangs when Changing VLAN on Port

Tried a different port on same blade and different blade. The issue did not reproduce. Good point though.

Maybe resolved but not clear on the why part. I did a "clear port sec 4/32 all" command then plugged back into the offending port. I am now able to assign different vlans with no hanging it seems. CPU also remains steady.

Re: VTY Session Hangs when Changing VLAN on Port

Danny, thanks for the update.. watch that port 4/32 , it may not be the system otherwise it would have replicated .



New Member

Re: VTY Session Hangs when Changing VLAN on Port

Jorge.....Thanks as well.


CreatePlease to create content