Virtual Switching System (VSS) is a method to combine two physical switches into one logical switch to achieve physical redundancy, Spanning-Tree blocking elimination, and increased bandwidth. VSS was first available in Cisco 6500 but it has recently been introduced to Cisco 4500 and 4500X. This article provides configuration that will allow you to easily enable VSS on these switches.

Background Information

While a similar technology (Multi-Chassis Etherchannel, MEC) exists in Nexus datacenter switches known as vPC, the Nexus switches only appear to other adjacent switches as one switch across L2 links while maintaining two separate control planes and management points. VSS actually does a better job of emulating a single switch with one active, and one (or more) standby control plane allowing it to fully support a dual-homed L3 routed link. If you are familiar with Cisco Stackwise technology in 3750/3850 switches, VSS is probably more comparable to those except VSS only supports up to two switches and instead of using Stackwise cables, it uses multiple 10G links for interconnecting switches (ie. VSL).

VSS on Cisco 6500

Requirements

Virtual Switching Supervisor 720-10GE (VS-S720-10GE-3C and VS-S720-10GE-3CXL) with IOS 12.2(33)SXH1 and IP Base

or Supervisor 2T (VS-S2T-10G and VS-S2T-10G-XL) with IOS 12.2(50) SY and IP Base

Note: Please check Cisco documentation for more detail

Cabling Between Chassis

Minimum of two 10Gbps links with at least one on the Supervisor

Minimum of one (more is recommended) 1Gbps or 10Gbps links for dual-active detection

Dual Active Detection Method

There are three available options; BFD, Fast Hello, Enhanced PAgP. EPAgP requires a downstream switch that is EPAgP-capable, which is sometime hard to find. BFD requires an IP address to be configured on the interface. Here we choose to use Fast Hello, although more than one method can be configured.

Configuration Steps:

Make sure all cabling between two switches are completed before proceeding

On Switch 1

1. Set switch number to 1

! switch set switch_num 1 local switch read switch_num local ! confirm 1 is returned !

2. Configure virtual domain then save config

! configure terminal switch virtual domain 1 switch 1 mac-address use-virtual ! optional but recommended ! do wr mem !

3. Configure VSL links.

! interface Port-channel 1 desc --- To Switch 2 VSL --- switchport switch virtual link 1 no shut ! interface range TenGigabitEthernetx/x-y ! modify as necessary channel-group 1 mode on no shutdown ! do wr mem exit !

4. Convert switch to VSS mode. Confirm and switch will reload

! switch convert mode virtual !

On Switch 2

1. Set switch number to 2

! switch set switch_num 2 local switch read switch_num local ! confirm 2 is returned !

2. Configure virtual domain then save config

! configure terminal switch virtual domain 1 switch 2 mac-address use-virtual ! optional but recommended ! do wr mem !

3. Configure VSL links.

! interface Port-channel 2 ! must be different number from switch 1 desc --- To Switch 1 VSL --- switchport switch virtual link 2 no shut ! interface range TenGigabitEthernetx/x-y ! modify as necessary channel-group 2 mode on no shutdown ! do wr mem exit !

4. Convert switch to VSS mode. Confirm and switch will reload

! switch convert mode virtual !

Wait until switch 2 comes back and join VSS

You can only make config changes on the active supervisor now

On the active switch

1. Adjust switch priority

! configure terminal switch virtual domain 1 switch 1 priority 110 switch 2 priority 100 !

2. Configure dual-active detection

! switch virtual domain 1 dual-active detection fast-hello ! interface ra GigabitEthernet1/x/x ! modify as necessary desc --- VSL Fast Hello --- dual-active fast-hello no shutdown ! interface ra GigabitEthernet2/x/x ! modify as necessary desc --- VSL Fast Hello --- dual-active fast-hello no shutdown exit ! show switch virtual dual-active fast-hello ! verify !

VSS on Cisco 4500/4500X

Requirements

Supervisor Engine 7-E (WS-X45-Sup7-E) (IP Base)

Or Supervisor Engine 7L-E (WS-X45-Sup7L-E) (Enterprise Services)

Or 4500X Switch Family (IP Base)

Minimum IOS XE 3.4.xSG

IOS XE 3.5.0E for L3 MEC and Fast Hello Dual-Active Detection support (Recommended)

Note: Please check Cisco documentation for more detail

Cabling Between Chassis

Minimum of two 10Gbps links with at least one on the Supervisor (4500 Only)

Minimum of one (more is recommended) 1Gbps or 10Gbps links for dual-active detection

Dual Active Detection Method

Only Enhanced PAgP used to be supported but, as of 3.5.0E, Fast Hello is made available. EPAgP requires a downstream switch that is EPAgP-capable, which is sometime hard to find. Here we choose to use Fast Hello, although more than one method can be configured.

Configuration Steps:

Make sure all cabling between two switches are completed before proceeding

On Switch 1

1. Configure virtual domain then save config

! configure terminal switch virtual domain 1 switch 1 mac-address use-virtual ! optional but recommended ! do wr mem !

2. Configure VSL links.

! interface Port-channel 1 desc --- To Switch 2 VSL --- switchport switch virtual link 1 no shut ! interface range TenGigabitEthernetx/x-y ! modify as necessary channel-group 1 mode on no shutdown ! do wr mem exit

3. Convert switch to VSS mode. Confirm and switch will reload

! switch convert mode virtual !

On Switch 2

1. Configure virtual domain then save config

! configure terminal switch virtual domain 1 switch 2 mac-address use-virtual ! optional but recommended ! do wr mem !

2. Configure VSL links.

! interface Port-channel 2 ! must be different number from switch 1 desc --- To Switch 1 VSL --- switchport switch virtual link 2 no shut ! interface range TenGigabitEthernetx/x-y ! modify as necessary channel-group 2 mode on no shutdown ! do wr mem exit !

3. Convert switch to VSS mode. Confirm and switch will reload

! switch convert mode virtual !

Wait until switch 2 comes back and join VSS

You can only make config changes on the active supervisor/switch now

On the active switch

1. Adjust switch priority

! configure terminal switch virtual domain 1 switch 1 priority 110 switch 2 priority 100 !

2. Configure dual-active detection