Catalyst 3750 series is the only series that can do switch stacking, Cisco call this Stackwise technology, the later switch also includes Energywise technology which is to optimize the energy utilization for each switch in a switch stack.
A switch stack is described as multiple switches stacked together to form a single unit, this is very similar to the 4500 and 6500 series switches, it is similar but not the same. To the network a switch stack is a single switch with multiple slots.
Supposed your switch stack is under utilized, your boss requires a switch (let’s call it SS-1) to be taken out from the switch stack to temporary replaced a single WS-3750G-24TS (let’s call it SW-1) unit which is sent for maintenance.
Since SS-1 is the same model as the SW-1, you load SW-1′s config file into SS-1. Supposed you forgot to check and just deployed SS-1, users complaints of lost of network connectivity after SW-1 was replaced with SS-1.
Troubleshooting found out that SS-1 has no vlan database, and vlan.dat has not been backed up from SW-1. You spent some time to re-create the vlan database and assign vlan membership to the respective ports. However users still complained there’s no connectivity.
You issued the show vlan brief command, and found that there’s no ports assigned to the respective vlan. You check the start-up config and found all respective ports have been assigned to the vlans. You also noticed that the gigabit ethernet ports are labeled as gi3/0/x instead of gi1/0/x.
Switch/Stack Mac Address : 0817.358d.ea00
Switch# Role Mac Address Priority Version State
1 Member 0000.0000.0000 1 0 Provisioned
*3 Master 0817.35ba.ec80 1 0 Ready
SS-1 was previously from a switch stack slot 3, you thought loading the config file will erase the switch status, but you were wrong.
Easier solution to rectify
From global configuration mode:
switch 3 renumber 1
You then issued show vlan brief, now all the ports are in the respective vlans.
Attention to detail is necessary, try not to rush, the best is to write down a check list of what are the things that you should do.