Configuring Stack Power, what they DON'T tell you

Hi Guys

So their is a guide to configuring Stack Power for 3750x's available at:
http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_58_se/configuration/guide/swstkpwr.html#wp1015591

However, to say it is incomplete would be an understatement. If you just read this document, it appears all you have to do is plug the power cables in and away it goes, this however is not accurate, and sometimes it can be a little flakely, so without further ado, please enjoy my guide on getting stack power configured:

Step 1.
Get all your switches powered up using their own power, stack them together as a data stack, The directions change a little bit if your not using a stack OR if you don't have enough power cables and want to just get a few switches up using only one power cable, Your directions are a little diffirent. Leave a comment if you need help.



Step 2.
So, first of all you need to issue a command like such:


show stack-power

Power stack name: Powerstack-1
Stack mode: Power sharing strict
Stack topology: Standalone
Switch 3:
Power budget: 1063
Low port priority value: 22
High port priority value: 13
Switch priority value: 4
Port 1 status: Shut
Port 2 status: Shut
Neighbor on port 1: 0000.0000.0000
Neighbor on port 2: 0000.0000.0000

If you look at this output, the key words are Port 1 Status: Shut and Port 2 Status: Shut

This means that the stack power is not turned on yet on those ports, to turn it on issue this command:


switch1#stack-power switch 1 port 1 enable
switch1#stack-power switch 1 port 2 enable

This will enable stack power across the ports, you need to do this on every switch in your stack, so for example:

switch1#stack-power switch 2 port 1 enable
switch1#stack-power switch 2 port 2 enable

and so on and so forth for each switch, now you should also ensure all your switches are part of the same Power Stack (each switch can belong to one power stack group)

#show stack-power

Power stack name: Powerstack-1
Stack mode: Power sharing strict
Stack topology: Ring
Switch 1:
Power budget: 343
Low port priority value: 21
High port priority value: 12
Switch priority value: 3
Port 1 status: Connected
Port 2 status: Connected
Neighbor on port 1: 44d3.ca71.1c00
Neighbor on port 2: 44d3.ca70.0e00

Switch 2:
Power budget: 373
Low port priority value: 20
High port priority value: 11
Switch priority value: 2
Port 1 status: Connected
Port 2 status: Connected
Neighbor on port 1: 44d3.ca71.1b80
Neighbor on port 2: 44d3.ca71.1c00

Switch 3:
Power budget: 343
Low port priority value: 22
High port priority value: 13
Switch priority value: 4
Port 1 status: Connected
Port 2 status: Connected
Neighbor on port 1: 44d3.ca70.0e00
Neighbor on port 2: 44d3.ca71.1b80



the configuration to place them all in the same group like this is shown below:

stack-power stack Powerstack-1
stack-power switch 1
stack Powerstack-1
stack-power switch 2
stack Powerstack-1
stack-power switch 3
stack Powerstack-1

This will place all three switches into the same power stack.

Now finally, the next step is to configure any parameters we might want such as setting one switch to have a higher priority than the other.

So, every switch has a priority, the higher priority switches have there power shedded first (confusing i know)

within the switch, there are also high-priority POE ports and low-priority POE Ports, you set your high priority POE ports with a lower value and your low-priority ports with a higher value

Note that a switches priority must be LOWER than its own ports, you could also use these values to make it so that, lets say you had three switches, you could say if you need to shed power, shed power from the low-priority POE ports for switch 1 and 2 first, THEN if still not enough power just shut down switch 3, then if still not enough power shut down switch 2 then 1

so you can see you can really ensure that each switch has a particular priority and same for the ports

Here is an example



switch#show stack-power
Power stack name: Powerstack-1
Stack mode: Power sharing strict
Stack topology: Ring
Switch 1:
Power budget: 343
Low port priority value: 11
High port priority value: 10
Switch priority value: 1
Port 1 status: Connected
Port 2 status: Connected
Neighbor on port 1: 44d3.ca71.1c00
Neighbor on port 2: 44d3.ca70.0e00

Switch 3:
Power budget: 343
Low port priority value: 15
High port priority value: 14
Switch priority value: 3
Port 1 status: Connected
Port 2 status: Connected
Neighbor on port 1: 44d3.ca70.0e00
Neighbor on port 2: 44d3.ca71.1b80

Switch 2:
Power budget: 373
Low port priority value: 13
High port priority value: 12
Switch priority value: 2
Port 1 status: Connected
Port 2 status: Connected
Neighbor on port 1: 44d3.ca71.1b80
Neighbor on port 2: 44d3.ca71.1c00

In this example, low priority ports on switch 3 are shed first, then the high priority ports

then on switch 2, low priority ports are shed first, then high priority

then on switch 1, low priority ports are shed first, then high priority

Finally, if enough power is not available with all POE ports turned off, switch 3 is turned off first, followed by switch 2, then switch 1


However, in the example above we have enough power to power all three switches with one power supply