StackWise Virtual Configuration on Catalyst 9606R

In this post, I will show you how to configure StackWise Virtual on a pair of Cisco Catalyst 9606R switches.

Cisco StackWise Virtual is a switch virtualization technology that combines two switches into one virtual switch. StackWise Virtual simplifies network management since you can manage one stack of switches instead of each switch independently.

In other words, through Cisco StackWise Virtual, two physical switches can be managed as a single logical virtual switch.

StackWise Virtual Design

In addition to giving you the commands to configure StackWise Virtual on the 9606R switches, I will show you how to select what ports to use on the StackWise Virtual Link (SVL) and potentially for the uplink to a Layer 3 Aggregation core.


StackWise Virtual Sample Configuration

StackWise Virtual Design with Catalyst 9606R Switches

The section below provides the StackWise Virtual commands to be applied on Catalyst 9606R Switch 1.

switch priority 15

config terminal

 domain 10

interface range hu1/0/39,hu1/0/47,hu2/0/39,hu2/0/47
 enable ! turn on 100 Gbps support
 stackwise-virtual link 1

write mem

The following StackWise Virtual commands need to be applied on Catalyst 9606R Switch 2.

switch renumber 2 ! switch ID will become switch 2 after reload
switch priority 14 ! Optional - default is 1

config terminal

 domain 10

interface range hu1/0/39,hu1/0/47,hu2/0/39,hu2/0/47
 enable ! turn on 100 Gbps support
 stackwise-virtual link 1



The above CLI configuration assumes the following hardware on the Catalyst 9606R pair of switches.

  • Slot 1: C9600-LC-24C
  • Slot 2: C9600-LC-24C
  • Slot 3: C9600-SUP-1
  • Slot 4: C9600-SUP-1
  • Slot 5: C9600-LC-48YL
  • Slot 6: empty

I hear you asking: why did Rio use hu1/0/39, hu1/0/47, hu2/0/39, and hu2/0/47 to create the StackWise Virtual Link? Because I wanted to include in the StackWise Virtual Link ports associated with different ASICs.

When a line card is installed on a 9606R chassis, one-third of its ports are connected to one of the three ASICs. In other words, one-third of the ports on the line card is connected to ASIC 0, the second set is to ASIC 1, and the third set of ports are connected to ASIC 2.

Catalyst 9606R StackWise Virtual Link Interfaces

Here’s a visual of the port numbering assignment on the C9400-LC-24C line card with C9600-SUP-1 and C9600-SUP-2 and their ASIC mapping.

Forty Gigabit Ethernet Port Numbering & ASIC Assignment on C9400-LC-24C

You have to use the “enable” command under a Hundred Gigabit Ethernet interface to turn on 100 Gbps support. When the Catalyst 9606R is powered by a C9600-SUP-1, the switch disables the bottom port. For instance, when you enter the commands below on Hu1/0/25, the switch disables the bottom Forty Gigabit Ethernet port, Fo1/0/2.

interface Hu1/0/25
Hundred Gigabit Ethernet Port Numbering & ASIC Assignment on C9400-LC-24C with SUP-1

When instead of using a SUP-1, you use C9600-SUP-2 supervisor module, the switch allows having all 24 Hundred Gigabit Ethernet ports activated.

Hundred Gigabit Ethernet Port Numbering & ASIC Assignment on C9400-LC-24C with SUP-2

You can verify all these ASIC-to-physical port mappings with the command show platform software fed active ifm mapping.

As you can see, for critical port channels, you can spread the port channel member links across ASICs for better performance and redundancy.


StackWise Virtual Dual Active Detection Sample Configuration

If the StackWise Virtual Link is lost, the standby switch will think that the active switch is lost, and therefore, the standby will become active. When you have two active core switches with the same IP addresses on all routed and Switched Virtual (SVI) interfaces, you run into duplicate IP issues.

To avoid this scenario, you can configure a Dual Active Detection link as follows.

interface range TwentyFiveGigE1/5/0/48,TwentyFiveGigE2/5/0/48
 stackwise-virtual dual-active-detection

Notice that after the StackWise virtual switch is created, your port numbering scheme changes.

The first number represents the chassis ID. The second number tells you the module number within that chassis. And the fourth number is the port on that module.


StackWise Virtual Best Practices

I recommend the following Cisco StackWise Virtual best practices:

  • Use a StackWise Virtual domain ID between 1 and 255 to avoid conflict in the network. The default is domain ID 1.
  • Use a Switch ID between 1 and 9. I always use 1 and 2. I configure the switch on the left or on top (one switch atop the other) as Switch 1.
  • The default Switch priority is 1 and the highest is 15. Cisco recommends increasing the priority of one of the switches to make it more likely to become the active switch. I always configure Switch 1 with a priority of 15 to pre-determine what switch becomes the active switch. To become active, a higher priority is preferred.
  • Stack MAC address: Default is infinite. Cisco recommends keeping default settings.
  • You should configure the StackWise Virtual link as a multiple-link port channel and spread it across multiple ASICs if possible as well as multi-line cards.

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I hope this post was useful to you.

I would love to hear from you. Any comments, please them below.

Thank you!

Alirio Zavarce Faceshot


Alirio Zavarce, CCIE #28672, is a seasoned enterprise route-switch consultant with 30 years of experience with data networks. Alirio started this networking blog to help his peers become better network engineers and share all his everyday experiences and troubleshooting tips. More about me...

If Alirio had to prepare to take it again, here's what he would do to pass the CCIE lab.

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15 thoughts on “StackWise Virtual Configuration on Catalyst 9606R”

  1. I have known Sir Alirio as I affectionately call him. I have known him for a very short time when I was scratching my head on a project that was involving a dual service provider without BGP and I needed to use IP SLA and some advanced Cisco switching technologies like StackWise and he guided me throughout the whole process and mentored me in a very unique way to achieve what I was looking for. I will recommend this blog to every network engineer who wants to really learn more about network design.

    Thank you

    • Thanks for your comment, Ben! Just trying to make it easier for those configuring StackWise Virtual on Catalyst 9606Rs and other switches from the Catalyst 9000 family that support StackWise Virtual.

  2. Hi Thank you for the great article.
    I have a quick question. if we have only one line card (Cisco Catalyst 9600 Series 48-Port 25GE/10GE/1GE) can this card has been used for SVL link and as well as for the downstream uplinks?

  3. Hi Alirio , I have a question, if I first configure the stackwise virtual architecture on the two C9600s on the ground and shut down the two devices after the configuration is complete. Then put it on the shelf and start a C9600-2, and connect it to the Internet line. Can the C9600-2 here work? Will it become an active switch first?
    If C9600-2 can work, will they be able to form a stackwise virtual architecture and not interrupt the network services of C9600-2 when they are put on the shelf, connected to the network line (including SVL) and started C9600-1?

    • Hi Kane1452. Yes, if after configuring the StackWise Virtual with the two 9600s you turn on C9600-2 by itself, it should work without C9600-1. And since it’s the only switch in the stack, it should become the active switch. If you then wired up the StackWise Virtual Link and the Dual-Active-Detection connection and turn on C9600-1, this switch should be added to the stack that was already configured and without interruptions. If C9600-2 is already in production, you should add C9600-1 during a maintenance window, just in case!

  4. Hi Alirio,
    Many thanks for this article and very good explaination about Stackwise virtual. I would like to ask that if Cisco StackWise Virtual is supported on Cisco Catalyst 9400 Series on Supervisor 2? Because it is mentioned in the Cisco document it support only sup-1 and not mentioned abut Sup2.

    Looking forward to hear from you.

    Thanks again.
    Mohammed Abdul Mannan

  5. We are planning to migrate CAT 6509-V-E switch migration to CAT 9609R switches. Can you suggest how to go about this.
    VSS and VRF is implemented in the existing 6509-V-E.

    • Hi Manesh. There are many things to consider. You can configure the new cores and move everything all at once, or you can gradually move all connections over. That latter will require connectivity between the old and new cores.

      I’d suggest you connect the two cores, 6509 and 9609, with a Layer 2 port channel and allow all VLANs. Make the 9609 the secondary STP root so when you connect the Layer 2 port channel, there’s no STP convergence. You can then move Layer 2 connections over to the 9609 and still keep connectivity to the SVIs that still live on the 6509. If you have port channels coming from the IDFs, you’ll need to move all port channel members at the same time because the two cores are two separate entities. If you have Layer 3 connections from the IDFs, you’ll need a routing VLAN between the two cores so they can exchange routes.

      After you have moved Layer 2 connections, you can start with Layer 3 interfaces. When you shut down an SVI on the 6509 and bring it up on the 9609, you want the 9609 to advertise the 6509 over the routing VLAN that subnet that was just moved. That way the 6509 knows that the subnet that was just moved is now reachable through the 9609.

      Keep in mind that you can split the migration in Layer 2 and Layer 3 phases. The goal is to know what was the last change that caused something to break. You can revert or troubleshoot quickly on the spot.

      I hope this helps.


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