I'm troubleshooting a problem where i disconnected a switch that was replaced by a new switch on a new network, my admin thought we could disconnect the old network equipment one by one after we had the new network equipment stood up and online. When i went to do this, after disconnecting the first switch, we started to see alerts from our network monitoring tool that devices (switches) were offline, They were not down, but we could not continously ping them. imguessing thats the reason the montioring tool reported them as down. Eventually we saw brief interruptions to traffic flow so my admin told me to reconnect the old switch. After doing so i have been going to each switch in the physical network and logging in and documenting the results or the following commands,
show version - to determine that devices base mac
show spanning-tree vlan 1 - to see what ports are involved, status and what each switch sees as the root bridge
show cdp neighbors - to help document connected devices and continue searching for root
while doing this on say 20 switches so far, i have found 3 different root bridges reported, i have only traced back and logged into 1 of them. The switch i mentioned above that is being blocked seems to be in the same topology as the switch i disconnected . It puzzled me why it seemed to be affected by topology changes when it didnt have a instance of stp for vlan 1 running, and then when i found another switch blocking it, i wondered more about it.
My company doesnt use Cisco DNA and doesnt have a graphical toplogy of the networks that cover two physically seperate campuses, so right now im remotely logging into switches and using those 3 commands to try and paint a picture of the networks, find the roots invloved and hopefully learn how to manage disconnecting the legacy network equipment without bringing down the new network.
I was hoping there was a tool or other commands that could help show stp members for a network, but i also think im going to learn alot researching this way.
Thanks for the help and answers thus far. Much appreaciated.
