Note that each stacking module has two ports with which it's used to connect it to another switch
stacking module.
So as an example, if you've got four switches, each switch has a stacking module and four cables are
used to connect the four switches together.
The way to think of this is the switches are a stack of switches in the same rack.
One of the reasons for doing that is that the stacking cables are very short in length.
So it's expected that the switches are physically positioned next to each other or on top of each other.
As an example, some of the Cisco stacking cables are only half a meter in length or one meter in
or three meters in length.
Again, you need to think of a switch stack as a logical single switch.
You may have four physical switches, but logically they're acting as one switch.
One of the switches in the stack becomes the stack master and it's used to control the rest of the switches
in the stack.
The physical stacking cables connect the physical switches to each other and allow for communication
between the switches in the stack.
But the master switch is in control of the stack.
If, as an example, you have four switches in a stack and a frame arrives on switch 4 and needs to
exit out of switch 3
but switch 1 is the master switch switches 1, 3 and 4 only to communicate over the stack
links to forward the frame. Switches 1, 3, and 4 would need to communicate with each other over
the stack links to forward the frame.
Switch 1 being the master switch would match the Ethernet frame to the Mac address table and would
then decide out of which port to forward the frame.
Think of the master switch as the brain of the stack.
Logically, in a topology like this, we have two physical switches, but logically they are a single
switch and the same would be true if we had four switches.
In a policy like this, we may have full access, which is connected via stacking cables, so physically
it would look like this.
But logically, it looks like this the switches appear to be a single switch to the rest of the network,
and you configure them as if they are a single switch.
We now have four uplinks to each distribution switch.
So physically they connected as follows with each axis switch having one connection to each distribution
switch
but logically, we have four physical cables to each distribution switch, which then allows us to use
ether channel to the distribution switch.
So rather than using spanning tree across these uplinks, where one of the ports is forwarding and one
of the ports is blocking.
We've now created an Ether channel to each distribution switch.
This kind of setup simplifies the configuration and management of the network, from a spanning tree
point of view
rather than having six switches involved in the spanning tree, we now only have three switches involved
in the spanning tree.
So it's much easier to configure, much easier to understand, as well as to predict what happens when
there's a failure in the network.
Uploading across an Ether channel is also more efficient than using spanning tree to block one port and
forward on another port.