Stack-power question

[pvezina]

Hello,

We have a stack of 3 x Cat3850-48T-S switches (no PoE). Each switch has one 350W power supply. Here's the output of the "show stack-power detail" command:

Power Stack          Stack  Stack   Total  Rsvd   Alloc  Unused Num Num
Name                 Mode   Topolgy Pwr(W) Pwr(W) Pwr(W) Pwr(W) SW  PS
-------------------- ------ ------- ------ ------ ------ ------ --- ---
Powerstack-1         SP-PS  Ring    1050   210    840    0      3   3

Power stack name: Powerstack-1
 Stack mode: Power sharing
 Stack topology: Ring
 Switch 2:
 Power budget: 280
 Power allocated: 280
 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: Switch 1 - 2834.a2b3.8100
 Neighbor on port 2: Switch 3 - 84b5.1755.1080

Switch 1:
 Power budget: 280
 Power allocated: 280
 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: Switch 2 - 2834.a2fd.5980
 Neighbor on port 2: Switch 3 - 84b5.1755.1080

Switch 3:
 Power budget: 280
 Power allocated: 280
 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: Switch 2 - 2834.a2fd.5980
 Neighbor on port 2: Switch 1 - 2834.a2b3.8100

Can someone explain the meaning of "Rsvd Pwr" and "Alloc Pwr" in the first table? In this scenario, if one switch loses a power supply, total power will go down to 700W. Will we have enough power then to power all three switches?

Thanks for your help,

Patrick.

[Masoud Pourshabanian]

Hello,

Please take a look at the link below. A lot of questions and answers regarding your inquery.

http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-3850-series-switches/qa_c67-722110.pdf

Masoud

[pvezina]

Hello,

So if I understand correctly, each switch reserves 280W for operation, even if the switch does not actually consume that amount of power (the datasheet says that a 3850-48T switch with a 4 x 10G NM actually uses about 120W). 

Then if I unplug a power supply in my stack that switch will shut down? (700W available, 840W needed)

Thanks.

[Masoud Pourshabanian]

Hello,

show power inline police

Check this command to see the actual power is used by switches. If actuall power usage is less than allocated, you should implement redundant mode instead of sharing. Because sharing may cause shuting down of one the switches if reserve is not enough. In your case, I guess one of your switces will be shutdown in case of power failure. To completely make sure, in downtime, cut power of one of the switches and check if the amount of allocation will change or not, but I do not think allocation is dynamic.

Please check the link below.

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/int_hw_components/configuration_guide/b_int_3se_3850_cg/b_int_3se_3850_cg_chapter_01000.html

Masoud

[elafJasim]

Hi Everybody,

would you explain the following questions please,  

Q1:

The meaning of "Rsvd Pwr", "Unused Pwr" and "Alloc Pwr" in the tables below?

@ Masoud:Because in the links that you have posted, there is nothing mentioned  or explained about these terms?

the show stack-power detail as shown in Case 1 has only one (Powerstack-11) power stack formed but after i did the following command 

CoreSwitch#stack-power switch 3 port 1 disable

CoreSwitch#stack-power switch 4 port 2 disable

then 

CoreSwitch#stack-power switch 3 port 1 enable

CoreSwitch#stack-power switch 4 port 2 enable

The stack configuration has been changed as shown in Case 2

Q2:

Do you know what is the reason that make the switch to form a new stack ring (Powerstack-1) as shown in CASE2 below?

Q3:

Unused Pwr (W) for Powerstack-1 was 0 but later has been changed to -280 in CASE3. any idea why the nummber has been Changen?

just for information, there is NO PoE device is connected to stacked switch!

CASE1:

CoreSwitch#show stack-power detail
Power Stack     Stack        Stack      Total           Rsvd        Alloc      Unused     Num Num
Name                Mode       Topolgy    Pwr(W)      Pwr(W)    Pwr(W)   Pwr(W)    SW   PS
--------------------  ------        -------       ------            ------        ------        ------         ---      ---
Powerstack-11  SP-PS     Ring       1400            840         1120       -560          4         4

Power stack name: Powerstack-11
Stack mode: Power sharing
Stack topology: Ring
Switch 3:
Power budget: 280
Power allocated: 280
Low port priority value: 22
High port priority value: 13
Switch priority value: 4
Port 1 status: Not connected
Port 2 status: Connected
Neighbor on port 1: 0000.0000.0000
Neighbor on port 2: Switch 1 - 5067.aefc.9000

Switch 4:
Power budget: 280
Power allocated: 280
Low port priority value: 19
High port priority value: 10
Switch priority value: 1
Port 1 status: Connected
Port 2 status: Not connected
Neighbor on port 1: Switch 2 - 5067.aefc.a100
Neighbor on port 2: 0000.0000.0000

Switch 2:
Power budget: 280
Power allocated: 280
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: Switch 1 - 5067.aefc.9000
Neighbor on port 2: Switch 4 - 3462.8813.4d80

Switch 1:
Power budget: 280
Power allocated: 280
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: Switch 3 - 3462.8892.7880
Neighbor on port 2: Switch 2 - 5067.aefc.a100

CASE2:

CoreSwitch#show stack-power detail
Power Stack          Stack     Stack      Total        Rsvd      Alloc     Unused    Num Num
Name                     Mode    Topolgy    Pwr(W)   Pwr(W)  Pwr(W) Pwr(W)    SW   PS
--------------------      ------       -------       ------         ------      ------      ------         ---    ---
Powerstack-11      SP-PS    Ring        700          420       560       -280          2      2
Powerstack-1       SP-PS     Ring        700         140        560        0              2      2

Power stack name: Powerstack-11
Stack mode: Power sharing
Stack topology: Ring
Switch 2:
Power budget: 280
Power allocated: 280
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: Switch 1 - 5067.aefc.9000
Neighbor on port 2: Switch 4 - 3462.8813.4d80

Switch 1:
Power budget: 280
Power allocated: 280
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: Switch 3 - 3462.8892.7880
Neighbor on port 2: Switch 2 - 5067.aefc.a100

Power stack name: Powerstack-1
Stack mode: Power sharing
Stack topology: Ring
Switch 3:
Power budget: 280
Power allocated: 280
Low port priority value: 22
High port priority value: 13
Switch priority value: 4
Port 1 status: Not connected
Port 2 status: Connected
Neighbor on port 1: 0000.0000.0000
Neighbor on port 2: Switch 1 - 5067.aefc.9000

Switch 4:
Power budget: 280
Power allocated: 280
Low port priority value: 21
High port priority value: 12
Switch priority value: 3
Port 1 status: Connected
Port 2 status: Not connected
Neighbor on port 1: Switch 2 - 5067.aefc.a100
Neighbor on port 2: 0000.0000.0000

CASE3:

CoreSwitch#show stack-power detail
Power Stack          Stack     Stack      Total        Rsvd      Alloc     Unused    Num Num
Name                     Mode    Topolgy    Pwr(W)   Pwr(W)  Pwr(W) Pwr(W)    SW   PS
--------------------      ------       -------       ------         ------      ------      ------         ---    ---
Powerstack-11      SP-PS    Ring        700          420       560       -280          2      2
Powerstack-1       SP-PS     Ring        700         140        560       -280          2      2

Power stack name: Powerstack-11
Stack mode: Power sharing
Stack topology: Ring
Switch 2:
Power budget: 280
Power allocated: 280
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: Switch 1 - 5067.aefc.9000
Neighbor on port 2: Switch 4 - 3462.8813.4d80

Switch 1:
Power budget: 280
Power allocated: 280
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: Switch 3 - 3462.8892.7880
Neighbor on port 2: Switch 2 - 5067.aefc.a100

Power stack name: Powerstack-1
Stack mode: Power sharing
Stack topology: Ring
Switch 3:
Power budget: 280
Power allocated: 280
Low port priority value: 22
High port priority value: 13
Switch priority value: 4
Port 1 status: Not connected
Port 2 status: Connected
Neighbor on port 1: 0000.0000.0000
Neighbor on port 2: Switch 1 - 5067.aefc.9000

Switch 4:
Power budget: 280
Power allocated: 280
Low port priority value: 21
High port priority value: 12
Switch priority value: 3
Port 1 status: Connected
Port 2 status: Not connected
Neighbor on port 1: Switch 2 - 5067.aefc.a100
Neighbor on port 2: 0000.0000.0000