[Cisco C9000] Command log that you want to acquire when configuring the stack and notes on stack mode

Table of contents

Target environment
Command log that you want to acquire when configuring the stack (at the time of construction)
Precautions in 1+1 mode
1. About role transition in case of failure
2. About starting the Member switch
References

Target environment

C9000 Series switches
- version 17.3.x

Command log that you want to acquire when configuring the stack (at the time of construction)

This section describes which command log should be acquired as a normality check during construction when configuring a stack with C9000 series switches.

Since the normal log at the time of construction is a useful isolation material when trouble occurs at the time of local introduction, it is very important to acquire and store it.

The command list is as follows.

show switch detail
show switch stack-mode
show romvar

show switch detail

First is show switch detail. I think this is a command that goes without saying, but you can see the following information.

Role：Active/Standby/Member
Mac Address
Priority
State：Switch state
Stack Port Status

C9000#show switch detail
Switch/Stack Mac Address : aaaa.aaaa.aaaa - Local Mac Address
Mac persistency wait time: Indefinite
                                             H/W   Current
Switch#   Role    Mac Address     Priority Version  State 
-------------------------------------------------------------------------------------
*1       Active   aaaa.aaaa.aaaa     15     V01     Ready                               
 2       Standby  bbbb.bbbb.bbbb     1      V01     Ready                               



         Stack Port Status             Neighbors     
Switch#  Port 1     Port 2           Port 1   Port 2 
--------------------------------------------------------
  1         OK         OK               2        2 
  2         OK         OK               1        1

show switch stack-mode

The second command is show switch stack-mode. I think that some people have never used this.

You can check the following information with this command.

Role：Active/Standby/Member
Mac Address
Mode：Stack mode (N+1 or 1+1)
Configured：Set stack role (role expected as the state after reboot)
State：Switch state

C9000#show switch stack-mode
Switch#  Role    Mac Address     Version   Mode  Configured  State 
--------------------------------------------------------------------------------------------------------------------
*1      Active   aaaa.aaaa.aaaa    V01     N+1     None       Ready               
 2      Standby  bbbb.bbbb.bbbb    V01     N+1     None       Ready

About stack mode

Few people have been aware of this, but the stack on C9000 series switches has two modes:

N+1
- Default mode
- The Mode value of the show switch stack-mode command is N+1
1+1
- Used to assign Active and Standby roles to specific switches in the stack
- If you specify a role with switch <スイッチ#> role <active|standby> command, it will automatically switch to 1+1 mode
- Stack manager determines Active and Standby roles based on flash ROMMON variables
- The Mode value of the show switch stack-mode command is 1+1

The display of show switch stack-mode when a role is specified by the switch <switch#> role command is as follows.

C9000#show switch stack-mode 
Switch#  Role    Mac Address     Version   Mode  Configured  State 
--------------------------------------------------------------------------------------------------------------------
*1      Active   aaaa.aaaa.aaaa    V01     1+1'    Active'    Ready               
 2      Standby  bbbb.bbbb.bbbb    V01     1+1'    Standby'   Ready

If the values in the Mode and Configured fields are marked with “‘” as above, it means that you have manually changed the settings.

To return the stack mode to N+1, execute the following command.

# switch clear stack-mode

If you change the stack mode, you need to reboot the entire stack.

show romvar

The third command is show romvar. You can check the ROMMON variable with this command.

In 1+1 mode, the ROMMON variable is involved in the operation. Therefore, it may be useful to check the ROMMON variable.

C9000#show romvar
----------------------------------
ROMMON variables for Active Switch
----------------------------------
ABNORMAL_RESET_COUNT=0
AUTOBOOT_COUNT=0
AUTOBOOT_STATE=0
#The following is omitted

It is recommended to acquire this command log even when the stack mode is N+1.

Precautions in 1+1 mode

About role transition in case of failure

In N+1 mode, the role changes as follows in the event of an Active / Standby switch failure.

In the event of an Active switch failure, the Standby switch will move to Active, and the member switch with the highest priority will move to Standby.
In the event of a Standby switch failure, the member switch with the highest priority shifts to Standby.

On the other hand, in 1+1 mode, the movement is as follows.

Standby switch transitions to Active in the event of an Active switch failure
The Member switch remains a Member in the event of an Active or Standby failure

About starting the Member switch

In 1+1 mode, if you try to activate another switch (Member role switch) in the absence of both Active or Standby-configured switches (down), the switches will look like this: It is not possible to restart repeatedly with a log.

Chassis N reloading, reason - Active/standby selection failed in 1+1 Mode

Member restarts also occur if both Active and Standby go down from the state in which each switch in the stack was up.

Chassis N reloading, reason - lost both active and standby

If you want to start the Member switch without the Active and Standby switches, you need to remove the relevant ROMMON variable on the Member switch.

Please refer to the following PDF for details.

【PDF】Catalyst 9000 Switches booting to switch: prompt due to Stack 1+1 variable

References

Stack Manager and High Availability Configuration Guide, Cisco IOS XE Amsterdam 17.2.x (Catalyst 9200 Switches) - Configuring 1:1 Redundancy [Support]

Configuring 1:1 Redundancy

Command Reference, Cisco IOS XE Gibraltar 16.12.x (Catalyst 9200 Switches) - System Management Commands [Cisco Catalyst 9200 Series Switches]

Command Reference, Cisco IOS XE Gibraltar 16.12.x (Catalyst 9200 Switches)-System Management Commands