Port mismatch error

[j_molineux]

I am new to networking and have a question about a problem I ran into. I have three switches - s1 is a 3560, s2 is a 2960 and s3 is a 2960.  S1 is connected to s2 and s2 is connected to s3.  When I took over the network segment I noticed that the links were all set up as access links across vlan 3.  I know I am going to need a couple more vlans in the future so decided to configure all them a trunks. Because the switches are all in different physical locations I decided to ssh into the switches to make the change.  To start I plugged into the console of s2 and ssh’d into s1. Knowing that as soon as I made the change I would have a mismatch error and the port would shut down, I first changed s1 using switchport more trunk.  As expected the link dropped.  What I didn’t expect was that I lost all ability to communicate with s2, which I was physically plugged in to.  I disconnected from s2 and plugged into s3.  I was able to ssh into s2 and make the same config change.  After going this I was able to communicate with s2 again via the console port.  Can anyone explain why the port mismatch would cause to lose the ability to communicate with s2 when I was plugged directly into the console.  Thanks in advance for any help in educating me.

[balaji.bandi]

Port mismatch expected since you moving from Access port to Trunk port.

as you mentioned you have these switches in different locations, did u get a chance to console access to SW1 and Sw2 to do the change that segment and then Sw2 and Sw3.

If not there are options :

Sw1 is remote, you can do EEM Script to make port shut and not shut (automatically it run background)

as soon as you change setting SW2 as trunk you should communicate back to switch with the VLAN you using for management, the same step for SW2 and SW3.

[j_molineux]

BB

thanks for the idea of using EEM script. I will look at that.  The bigger issue have is not the loss of connectivity between the ports, as you stated when the port on s2 is set to trunk I get those back.  My confusion is that when I initially lose conectivity between the ports. I also lose connectivity with the console on s2, which I am plugged in to.  

[balaji.bandi]

This is nothing to do with Console access ( Console means Serial cable right - for clarity) until Switch overloaded and kick you out.

Since the device is not reloaded, still you can look at the Logs that happened at that time. May be STP switch might have spiked the CPU.

[mlund]

Hi

I think this is what happens. Your connection from sw2 to sw1 is still active, so your sw2 is waiting for an answer from sw1. But since communication has been prohibited by the mismatch, the sw2 will not get an answer from sw1.

So there are 2 options to recover from this situation. First wait until the ssh session times out, or second option, simultanous press the "ctrl" and "shift" and "6" button, and just after that press "x", this will bring you back to your sw2 prompt. If you now press "enter" you will go back to your ssh session, and this is still not available, so do not press just enter, instead do "disconnect" "yes" "enter".

Now you are back to the normal state.

/Mikael