Putty connection error

[GShadwick81]

I have a Catalyst 3750G core switch. Up until last week Friday I was able to SSH via putty into my core switch and connect to others. Now every time I attempt to do so, I received I putty fatal error: Network connection refused. No changes have been made to the configuration from what I know. It is an extremely small domain that I am working with and I need to be able to find some way of connecting to the core so that I can in turn SSH into the other switches on the domain. I NEED HELP!!!

[Richard Burts]

If no config changes have been made there are a few things that could still cause these symptoms. My first guess would be that all of the available vty sessions are being used and the switch does not have an available vty for the new SSH session. Is it possible that your vty are configured with no inactivity timeout? (no exec-timeout or exec-timeout 0 0) Perhaps you can post the config of the vty ports?

There is also perhaps a possibility that there is an issue with IP connectivity (though that would usually result in a timeout and not a connection refused). Can you verify that you have IP connectivity by pinging the address that you attempt to SSH to?

HTH

Rick

[GShadwick81]

Hi Richard,

I am able to successfully ping the switch. I am trying to use a console cable from my laptop (with a USB-to-serial connecter) and it just holds there. The config setting I was using was as follows:

• Bits per second (baud): 9600

• Data bits: 8

• Parity: Even

• Stop bits: 1

• Flow Control: Xon/Xoff

I am unable to connect using putty or even hyperterminal.

[esa_fresa]

It looks like you don't have timeout configured on your lines, so all of the sessions may be used.

exec-timeout 0 0

I would enter a "clear line vty #" via the console connection, which you should be able to use since there can only be the one connection. Make sure you specify the correct line, ex. "COM4" if that's where your console is, rather than default "COM1".

[GShadwick81]

That is the problem, I have tried to use the console connection and even with the correct COM settings, it takes a long time to gain access, then it says "press RETURN to get started" but nothing works after that. I don't know if I should attempt a restore on this configuration or if there are any other options available for a resolution. I have never done a restore on and switch by the way!!

[esa_fresa]

It's possible that the CPU utilization is extremely high. It doesn't look like you have syslog or snmp configured, but that would be the place to check. You might also try logging in to the console line after hours when there's less traffic.

If you still can't get into the switch, there's not a whole lot more that can be done without CLI access. I would power cycle it during a maintenance window and try again.

[GShadwick81]

I read that if you do a power cycle that it erases the configuration of the switch. Is that true? If so then I would need to do a configuration restore and would need some guidance on doing that. Again... I am new to this and was inherited with this golden nugget.

[esa_fresa]

Sure, no problem.

The switch stores two configurations. First is the "startup-config", which is stored in NVRAM and loaded into RAM at boot. The config just loaded into RAM is now called the "running-config" and is what the switch actually uses.

Switches are happy to just be powered off, so just flip the switch off and on and it will start booting. Most likely the previous engineer saved the running-config to nvram so you won't have to make any changes, but if not it looks like you've got a backup. You can copy and paste the backup into the config mode of the switch. Be sure to save your changes with a "copy run start"

switch> en

switch# config t

switch(config)# <--- This is config mode.

[Richard Burts]

The config that you posted does confirm that the switch has disabled the inactivity timeout (exec-timeout 0 0). This allows sessions to go on being connected even after the user has stopped using the session and the result is that all of your vty connections are busy. This is the reason that you get the connection rejected error. I certainly suggest that when you do get access to the switch that you configure a value for the timeout. It can be a very long timeout if you want. But having some timeout configured will prevent the problem that you are now experiencing.

The best option would be to get access via the console port (or perhaps via the aux port). This should allow you to clear the vrty lines which would free up a session that would allow you to SSH again. I am not clear what you are saying about console access and whether you are eventually able to get access via the console.

If console/aux port access does not work then it may be that your only alternative is to power cycle the switch. It is not quite true that it erases the config of the switch. To understand the impact of power cycle the switch you need to understand that the switch has a copy of the config which is saved (called the startup config) and a copy of the currently active config (called the running config). When you power cycle the switch it erases the running config and then it boots using the startup config. So when you power cycle the switch you will end up running on the startup config. The potential issue is that if config changes have been made, but not saved to the startup then you will lose those config changes.

HTH

Rick

[GShadwick81]

Good morning from Miami!!

To follow up, being that there technically isn't any power button on the Catalyst 3750G, I can just simply unplug the power cord and plug back in to power cycle the switch? Also being that this is the core switch, none of the other switches on the domain will be affected besides the stack? The stack has 6 switches interconnected and I read that if you shut down the primary, another switch in the stack assume role of the master. 

My thought is simply that I can do a power cycle on the master switch and then simply paste the config backup to the switch and all will be fine. No changes have been made to that switch so the backup is current.

Lastly, how long does it take for the switch to power on?

[GShadwick81]

I was able to find a backup of the config on the switch and maybe this could shed some light to this. I apologize that I am new at this and I was inherited with this golden nugget. Attachment should be included.