Hi Everyone out there.
I have a situation that I need someone to explain what could have happened. I have a 2960 switch which was having a vlan flapping problem in one vlan - lets call it vlan 200. I was preparing to connect some more switches into the same vlan using and etherchannel. I created the etherchannel and placed the ports into the etherchannel and did a "no shut". All this without connecting any cables, the switch logged an up/down sequence event. The two switches are connected via a different port which is passing traffic with no issues. Can any try and help explain to me what could have happened here?
Thanks in Advance
I just recreated the same situation on my 2950 as you did on your 2960 for testing purposes. Here are my results:
I have currently 2 sessions open on the switch 1 console and 1 telnet ssh (this is not a live switch at this time so I use it for testing things regularly. no harm is actually being done lol). There are 2 cables curently hooked up to the switch, Console and 1 network plugged into fa0/1 in vlan1. I created 2 other vlans (2 and 3) and then creaed an eterchannel using fa 0/16 - 18. Everytime I issued a no shutdown command on one of the ports in the etherchannel I got an Up/down message on the console side. If I issued the commands on the console session I got them there as well. This is what I thought was going on. Everytime you issue a no shut command on a port it brings the status of said port to an active state (i.e. it powers it up and brings it online) whether anything is connected to it or not, causing the link up message, followed a second later with a link down message since it has no physical connection. This Should not have caused any convergance issues, and it shouldn't cause any routes to fail or affect stp at all as it is a normal operation of the switch. If you did lose paths in this process or cause a delay in any convergances then there may be other issues you need to investigate. But otherwise this is a normal message given by the switch when you bring any port online and active, cable or not.