Cisco Virtual Switching System (VSS)

ccnp-switching
Notes on the Cisco Virtual Switching System, covering how two chassis bond into one virtual switch and the domain, VSL, and conversion steps.
Published

Nov 21, 2017

VSS allows two identical Cisco Catalyst 4500R, 6500, or 8500 chassis (the chassis must contain a supervisor module that handles all the switch management functions) to bond together so that they are seen as a single virtual switch to the rest of the network.

Features

  • Non Stop Forwarding (NSF)
  • Stateful Switchover (SSO)
  • Enhanced Fast Software Upgrade (EFSU)

Configuration

In order to bond two chassis using VSS we will have to do the following:

  1. Configure a virtual switch domain on both chassis, and determine the master and standby switches by the switch ? priority ? command
  2. Configure the virtual switch links
  3. Execute the conversion command which will reboot the switches

Step 1

Configure a virtual switch domain on both chassis and configure one switch as switch 1 to become master and the other one as switch 2 to become standby 
SW1(config)#switch virtual domain 12
SW1(config-vs-domain)#switch 1
SW1(config-vs-domain)#switch 1 priority 110
SW1(config-vs-domain)#switch 2 priority 100
SW2(config)#switch virtual domain 12
SW2(config-vs-domain)#switch 2
SW2(config-vs-domain)#switch 1 priority 110
SW2(config-vs-domain)#switch 2 priority 100

Step 2

Configure the Virtual Switch Link. The virtual switch link is used to exchange configuration and stateful information between the two physical switches. You can use a single physical interface for VSL or create an etherchannel for redundancy.

Use the same configuration on SW1 for SW2 as well in this example: 
SW1(config)#interface port-channel 1
SW1(config-if)#no shutdown
SW1(config-if)#switch virtual link 1
SW1(config-if)#exit
SW1(config)#int range ten 1/4 - 5
SW1(config-if-range)#channel-group 1 mode on
SW1(config-if-range)#no shut

Step 3

Execute Conversion. Once we do this the switches will reload and 3 things will happen:

  • The configurations of both switches will be merged into a single configuration.
  • The interface numbers will be renumbered from slot/port to switch-number/slot/port.
  • Negotiation to determine which switch is active or standby.
SW1#switch convert mode virtual

Verification

SW#show switch virtual
SW#show switch virtual link
SW#show switch virtual role
SW#show interfaces vsl
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