Stack master election criteria
The criteria is in order, if the first criteria does not meet the second criteria will be the tie breaker.
1. The switch that is configured with the highest stack priority.
2. The switch that is not using the default configuration.
3. The switch that is using a higher priority IOS, the priority of the IOS types are as followed, in order of rank:
a. cryptographic IP services image that supports IPv6.
b. non-cryptographic IP services image that supports IPv6.
c. cryptographic IP services image that only supports IPv4.
d. non-cryptographic IP services image that only supports IPv4.
e. cryptographic IP base image.
f. non- cryptopgraphic IP base image.
4. The switch that has the longest uptime.
5. The switch that has the lowest mac address.
A stack supports up to 9 switches. A fully connected stack yields a 32Gbps backplane switching fabric, a partially connected stack yields a 16Gbps backplane fabric. Stackwise plus technology doubles the number of backplane fabric for both partially connected and fully connected. To understand how to connect partially or fully stack ports refer to this document.
To know more about Cisco stackwise technology download this document.
Unified switch chassis management
1. Switch stacks have one management vlan interface.
2. Switch stacks have a single vlan database.
3. Switch stacks interfaces are merged and renumbered. To increase the port density simply add another 3750 switch stack.
4. Cross stacks link aggregation.
5. Unified routing for all stacks. Since switches stacked together are effective one router chassis.
6. Allows users to pre-provision new 3750.
7. The switch stacks enjoy up to 32Gbps backplane switching fabric when fully connected.
8. When you issue command like reload the entire switch stacks reboot! When you issue command like write memory the entire switch stacks configurations are synchronized and stored in nvram.
Stackwise demonstration
Switch#sh switch
Switch/Stack Mac Address : 0013.c3f1.8d00
H/W Current
Switch# Role Mac Address Priority Version State
----------------------------------------------------------
*1 Master 0013.c3f1.8d00 5 0 Ready
2 Member 0018.b9b6.5000 1 0 Ready
Switch#
The master switch stack handles RIB, FIB and adjacency tables. The master switch stack also handles management interface, in conclusion master switch stack is like the brain of every stacks. The member stack is like the limbs of the master stack.
Suppose the master stack is dead, the next member stack takes over as master.
Switch#sh switch
Switch/Stack Mac Address : 0018.b9b6.5000
H/W Current
Switch# Role Mac Address Priority Version State
----------------------------------------------------------
1 Member 0000.0000.0000 0 0 Removed
*2 Master 0018.b9b6.5000 1 0 Ready
Switch#
This switch 2 will be master as long as it stays on, when switch 1 recovers from failure even if it has the highest stack priority switch 1 will never be the master unless switch 2 has a failure or the entire stacks reload.
Switch#sh switch
Switch/Stack Mac Address : 0018.b9b6.5000
H/W Current
Switch# Role Mac Address Priority Version State
----------------------------------------------------------
1 Member 0013.c3f1.8d00 5 0 Ready
*2 Master 0018.b9b6.5000 1 0 Ready
Switch#
The switch stacks interfaces are unified and renumbered, switch stack number directly affects the numbering of the interfaces, do not change the switch stacks numbering without very very strong reasons otherwise your previous interface specific commands will become invalid!
The below output is the entire interfaces renumbering, if you see FastEthernet1 and GigabitEthernet1 that means these ports are from switch 1, if you see FastEthernet2 and GigabitEthernet2 that means these ports are from switch 2.
Switch#sh ip int brief Interface IP-Address OK? Method Status Protocol Vlan1 10.10.10.1 YES TFTP up down FastEthernet1/0/1 unassigned YES unset down down FastEthernet1/0/2 unassigned YES unset down down FastEthernet1/0/3 unassigned YES unset down down FastEthernet1/0/4 unassigned YES unset down down FastEthernet1/0/5 unassigned YES unset down down FastEthernet1/0/6 unassigned YES unset down down FastEthernet1/0/7 unassigned YES unset down down FastEthernet1/0/8 unassigned YES unset down down FastEthernet1/0/9 unassigned YES unset down down FastEthernet1/0/10 unassigned YES unset down down FastEthernet1/0/11 unassigned YES unset down down FastEthernet1/0/12 unassigned YES unset down down FastEthernet1/0/13 unassigned YES unset down down FastEthernet1/0/14 unassigned YES unset down down FastEthernet1/0/15 unassigned YES unset down down FastEthernet1/0/16 unassigned YES unset down down FastEthernet1/0/17 unassigned YES unset down down FastEthernet1/0/18 unassigned YES unset down down FastEthernet1/0/19 unassigned YES unset down down FastEthernet1/0/20 unassigned YES unset down down FastEthernet1/0/21 unassigned YES unset down down FastEthernet1/0/22 unassigned YES unset down down FastEthernet1/0/23 unassigned YES unset down down FastEthernet1/0/24 unassigned YES unset down down GigabitEthernet1/0/1 unassigned YES unset down down GigabitEthernet1/0/2 unassigned YES unset down down FastEthernet2/0/1 unassigned YES unset down down FastEthernet2/0/2 unassigned YES unset down down FastEthernet2/0/3 unassigned YES unset down down FastEthernet2/0/4 unassigned YES unset down down FastEthernet2/0/5 unassigned YES unset down down FastEthernet2/0/6 unassigned YES unset down down FastEthernet2/0/7 unassigned YES unset down down FastEthernet2/0/8 unassigned YES unset down down FastEthernet2/0/9 unassigned YES unset down down FastEthernet2/0/10 unassigned YES unset down down FastEthernet2/0/11 unassigned YES unset down down FastEthernet2/0/12 unassigned YES unset down down FastEthernet2/0/13 unassigned YES unset down down FastEthernet2/0/14 unassigned YES unset down down FastEthernet2/0/15 unassigned YES unset down down FastEthernet2/0/16 unassigned YES unset down down FastEthernet2/0/17 unassigned YES unset down down FastEthernet2/0/18 unassigned YES unset down down FastEthernet2/0/19 unassigned YES unset down down FastEthernet2/0/20 unassigned YES unset down down FastEthernet2/0/21 unassigned YES unset down down FastEthernet2/0/22 unassigned YES unset down down FastEthernet2/0/23 unassigned YES unset down down FastEthernet2/0/24 unassigned YES unset down down GigabitEthernet2/0/1 unassigned YES unset down down GigabitEthernet2/0/2 unassigned YES unset down down Switch#
Now let me renumber the switch of the stacks and see the repercussion.
Switch(config)#switch 1 renumber 3 WARNING: Changing the switch number may result in a configuration change for that switch. The interface configuration associated with the old switch number will remain as a provisioned configuration. Do you want to continue?[confirm] Changing Switch Number 1 to Switch Number 3 New Switch Number will be effective after next reboot Switch(config)#
Type y to confirm, and reload.
Switch#sh switch
Switch/Stack Mac Address : 0013.c3f1.8d00
H/W Current
Switch# Role Mac Address Priority Version State
----------------------------------------------------------
1 Member 0018.b9b6.5000 1 0 Ready
2 Member 0000.0000.0000 0 0 Provisioned
*3 Master 0013.c3f1.8d00 5 0 Ready
Switch#
It is ok if the switch 2 is not present, however because switch 3 previously was 2 and there might be configuration that was related to switch 2 interfaces such as vlan members, now these configurations will become invalid. Let’s see the interfaces now.
Switch#sh ip int bri Interface IP-Address OK? Method Status Protocol Vlan1 10.10.10.1 YES NVRAM up down FastEthernet1/0/1 unassigned YES unset down down FastEthernet1/0/2 unassigned YES unset down down FastEthernet1/0/3 unassigned YES unset down down FastEthernet1/0/4 unassigned YES unset down down FastEthernet1/0/5 unassigned YES unset down down FastEthernet1/0/6 unassigned YES unset down down FastEthernet1/0/7 unassigned YES unset down down FastEthernet1/0/8 unassigned YES unset down down FastEthernet1/0/9 unassigned YES unset down down FastEthernet1/0/10 unassigned YES unset down down FastEthernet1/0/11 unassigned YES unset down down FastEthernet1/0/12 unassigned YES unset down down FastEthernet1/0/13 unassigned YES unset down down FastEthernet1/0/14 unassigned YES unset down down FastEthernet1/0/15 unassigned YES unset down down FastEthernet1/0/16 unassigned YES unset down down FastEthernet1/0/17 unassigned YES unset down down FastEthernet1/0/18 unassigned YES unset down down FastEthernet1/0/19 unassigned YES unset down down FastEthernet1/0/20 unassigned YES unset down down FastEthernet1/0/21 unassigned YES unset down down FastEthernet1/0/22 unassigned YES unset down down FastEthernet1/0/23 unassigned YES unset down down FastEthernet1/0/24 unassigned YES unset down down GigabitEthernet1/0/1 unassigned YES unset down down GigabitEthernet1/0/2 unassigned YES unset down down FastEthernet2/0/1 unassigned YES unset down down FastEthernet2/0/2 unassigned YES unset down down FastEthernet2/0/3 unassigned YES unset down down FastEthernet2/0/4 unassigned YES unset down down FastEthernet2/0/5 unassigned YES unset down down FastEthernet2/0/6 unassigned YES unset down down FastEthernet2/0/7 unassigned YES unset down down FastEthernet2/0/8 unassigned YES unset down down FastEthernet2/0/9 unassigned YES unset down down FastEthernet2/0/10 unassigned YES unset down down FastEthernet2/0/11 unassigned YES unset down down FastEthernet2/0/12 unassigned YES unset down down FastEthernet2/0/13 unassigned YES unset down down FastEthernet2/0/14 unassigned YES unset down down FastEthernet2/0/15 unassigned YES unset down down FastEthernet2/0/16 unassigned YES unset down down FastEthernet2/0/17 unassigned YES unset down down FastEthernet2/0/18 unassigned YES unset down down FastEthernet2/0/19 unassigned YES unset down down FastEthernet2/0/20 unassigned YES unset down down FastEthernet2/0/21 unassigned YES unset down down FastEthernet2/0/22 unassigned YES unset down down FastEthernet2/0/23 unassigned YES unset down down FastEthernet2/0/24 unassigned YES unset down down GigabitEthernet2/0/1 unassigned YES unset down down GigabitEthernet2/0/2 unassigned YES unset down down FastEthernet3/0/1 unassigned YES unset down down FastEthernet3/0/2 unassigned YES unset down down FastEthernet3/0/3 unassigned YES unset down down FastEthernet3/0/4 unassigned YES unset down down FastEthernet3/0/5 unassigned YES unset down down FastEthernet3/0/6 unassigned YES unset down down FastEthernet3/0/7 unassigned YES unset down down FastEthernet3/0/8 unassigned YES unset down down FastEthernet3/0/9 unassigned YES unset down down FastEthernet3/0/10 unassigned YES unset down down FastEthernet3/0/11 unassigned YES unset down down FastEthernet3/0/12 unassigned YES unset down down FastEthernet3/0/13 unassigned YES unset down down FastEthernet3/0/14 unassigned YES unset down down FastEthernet3/0/15 unassigned YES unset down down FastEthernet3/0/16 unassigned YES unset down down FastEthernet3/0/17 unassigned YES unset down down FastEthernet3/0/18 unassigned YES unset down down FastEthernet3/0/19 unassigned YES unset down down FastEthernet3/0/20 unassigned YES unset down down FastEthernet3/0/21 unassigned YES unset down down FastEthernet3/0/22 unassigned YES unset down down FastEthernet3/0/23 unassigned YES unset down down FastEthernet3/0/24 unassigned YES unset down down GigabitEthernet3/0/1 unassigned YES unset down down GigabitEthernet3/0/2 unassigned YES unset down down Switch#
I renumbered the switch from 3 to 1 by using switch 3 renumber 1 and switch 1 renumber to 2 and then reload.
Switch(config)#switch 3 renumber 1 WARNING: Changing the switch number may result in a configuration change for that switch. The interface configuration associated with the old switch number will remain as a provisioned configuration. Do you want to continue?[confirm]yChanging Switch Number 3 to Switch Number 1 New Switch Number will be effective after next reboot Switch(config)#sw Switch(config)#switch 1 renum Switch(config)#switch 1 renumber 2 WARNING: Changing the switch number may result in a configuration change for that switch. The interface configuration associated with the old switch number will remain as a provisioned configuration. Do you want to continue?[confirm]yChanging Switch Number 1 to Switch Number 2 New Switch Number will be effective after next reboot Switch(config)#
While waiting for it to finish POST let’s see the master stack election process during POST.
POST: CPU MIC register Tests : Begin POST: CPU MIC register Tests : End, Status Passed POST: PortASIC Memory Tests : Begin POST: PortASIC Memory Tests : End, Status Passed POST: CPU MIC interface Loopback Tests : Begin POST: CPU MIC interface Loopback Tests : End, Status Passed POST: PortASIC RingLoopback Tests : Begin POST: PortASIC RingLoopback Tests : End, Status Passed SM: Detected stack cables at PORT1 PORT2 Waiting for Stack Master Election... POST: Inline Power Controller Tests : Begin POST: Inline Power Controller Tests : End, Status Passed POST: PortASIC CAM Subsystem Tests : Begin POST: PortASIC CAM Subsystem Tests : End, Status Passed POST: PortASIC Stack Port Loopback Tests : Begin POST: PortASIC Stack Port Loopback Tests : End, Status Passed POST: PortASIC Port Loopback Tests : Begin POST: PortASIC Port Loopback Tests : End, Status Passed Election Complete Switch 2 booting as Member, Switch 1 elected Master HCOMP: Compatibility check PASSED Waiting for feature sync.... Waiting for Port download...Complete Waiting for Master Ready...Complete
Now there is an additional unwanted switch number 3, let’s remove it 🙂
Switch#sh switch
Switch/Stack Mac Address : 0013.c3f1.8d00
H/W Current
Switch# Role Mac Address Priority Version State
----------------------------------------------------------
*1 Master 0013.c3f1.8d00 5 0 Ready
2 Member 0018.b9b6.5000 1 0 Ready
3 Member 0000.0000.0000 0 0 Provisioned
Switch#
The command is very simple.
Switch#conf t Switch(config)#no switch 3 provision Switch(config)#
Conclusion
Stackwise provides network resiliency and simplified switch management process. I do not consider stackwise to be redundancy as in my opinion redundancy works in a pair of active standby units, only one unit is forwarding and the other unit is sleeping, in the case of stackwise all switches stacked together are unified and only one master stack is controlling the entire stacks, and all stacks are forwarding traffic if in a loop free topology. Stackwise is very easy to setup, basically you might only be interested in configuring the stack priority.
WARNING
Removing stackwise cable from the switch stack while the stack is turned on can cause stack reload.
Good Job
Thanx for the article!!!!!