In this blog, we are going to talk about VSS and tell you how to configure the VSS in the live environment. We will see the prerequisite and limitations for configuring VSS first and then will come up with the VSS configuration. The following topics will be covered in this blog:

  • Prerequisite for configuring VSS
  • Restrictions for Configuring VSS
  • Restriction for VSL
  • Restriction for MultiChassis EtherChannel (MEC)
  • VSS Configuration

Prerequisite for Configuring VSS

  1. Hardware Requirement:  The two chassis must have the same number of slots. VSS is available on Supervisor Engine 2T, 6T, and Supervisor Engine 720-10G. Thus, all supervisor engines or systems in a VSS must match precisely.

                 The following Supervisor Engine Model Numbers supporting VSS are:



  • VSL Hardware Requirement: The VSL EtherChannel supports both 10 gigabit Ethernet ports. The best recommendation is to use at least two of the 10 Gigabit Ethernet in a VSL port-channel.
  • Multichassis EtherChannel Requirement: Physical links from any of the supervisor engines or line-card modules can be used to implement a Multichassis EtherChannel (MEC).
  • Software Requirement: The VSS configuration in the startup-configuration file must match on both chassis.

Restrictions for VSS:

  •  We can cluster only 2 switches for VSS
  •  VSL link must have at least bandwidth of 10Gig
  •  While configuring VSS, both chassis must have the same number of line-card slots.
  • VSS mode does not support supervisor engine redundancy within a chassis.
  • If we configure a new value for switch priority, the change takes effect only after we save the configuration file and perform a restart.

Restrictions for VSL:

  • For the redundancy, we are recommended configuring at least two ports per switch for the VSL. For module redundancy, the two ports can be on different switching modules in each chassis.      
  • The ‘no platform qos channel consistency command is automatically applied when we configure the VSL. Do not remove this command.
  • VSL ports cannot be used as a SPAN source.

Restrictions for Multichassis EtherChannel (MEC):

  • All links in a MEC must be terminated on the active or standby chassis of the same virtual domain.
  • For a MEC using the LACP control protocol, the ‘minilinks’ command argument defines the minimum number of physical links in each chassis for the MEC to be operational.
  • For a MEC using the LACP control protocol, the ‘maxbundle’ command argument defines the maximum number of links in the MEC across the whole VSS.
  • A MEC can be connected to another MEC in a different VSS domain.

VSS Configuration:

Step-1: Configure virtual switch ID and domain


  VSS-sw1(config) # switch virtual domain 100                                

   VSS-sw1(config-vs-domain) # switch 1

   VSS-sw1(config-vs-domain) # exit

    Vss-sw1(config) # switch read switch_num


VSS-Sw-2(config) # switch virtual domain 100

VSS-sw-2(config-vs-domain) # switch 2

VSS-sw-2(config-vs-domain) #exit

Vss-sw-2(config) # switch read switch_num

Step-2: Configure the VSL port channel and member ports

           Vss-Sw (config) # interface port-channel 1

           Vss-sw (config-if) #switch virtual link 1

            Vss-sw(config-if) # no shut

            Vss-sw(config-if) # exit

            Vss-sw(config) # interface range tenGigabitEthernet 5/4-5

            Vss-sw(config-if-range) # channel group 1 mode on

            Vss-sw(config-if-range) # no shut

Step-3:  Convert to virtual switch mode

            Vss-sw # switch convert mode virtual

In this article, we have been through the minimum requirement for configuring VSS on multi-chassis switches. We also got aware of the restrictions for VSL & MEC. We hope, this VSS blog series will be helpful to all of you who are seeking to understand the VSS concept and looking for its configuration. We are available on WhatsApp at +919773973971 and we can discuss the requirements for your organization.

Sani Singh
Consultant – Enterprise Networking

Comments (2)

  1. Winston
    April 28, 2022

    I want to switch cause I can’t login to this device Google account?
    It requires security pin or password?
    And I don’t know it?

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