Virtual Switch System

Virtual Switch System
The Virtual Switch System 1440 (or VSS-1440) on the Catalyst 6500 is a mode of operation that virtualises two switches in to a single unit. At a minimum it requires a Supervisor 720-10GE to operate.


The primary benefit of this mode allows Multichassis EtherChannel (MEC) to occur. Additional benefits include a common configuration across two aggregation switches, NSF/SSO failover between chassis and the ability to avoid layer 3 in the access (desirable in a datacentre deployment) .


Architecture

At the heart of the Virtual Switching System, there is the Virtual Switch Link or VSL. The VSL is a dedicated 10GE link (or bundle of links) that are used to carry control plane traffic between VSS members.


The VSL essentially acts as an extension to the backplane, allowing control traffic to travel between chassis. As it uses existing X2 optics, the distance limitations of the VSS is limited only by supported 10GE ethernet standards.


When a VSS system is configured, the two chassis share a common configuration (see below for how this works). The devices also share a common MAC address and can truly load balance. In many ways, it is similar to how a Catalyst 3750 operates.


A common application is datacentre or high-end distribution where layer-2 links can etherchannel in to two chassis for high availability.


Hardware Requirements

The system must be running the Supervisor 720 10GE running PFC3C or PFC3CXL. In addition, any 10GE cards used for the VSL must be:

• 6708 (8-port 10GE line card) or Supervisor (Sup720-10GE) uplinks


• Using the DFC3C or DFC3CXL in conjunction with th PFC3C or PFC3CXL Supervisor

A caveat is that any DFCs in the system must also be upgraded to DFC3C or DFC3CXL. DFC3 and DFC3B and their XL equivalents are not supported. All line cards must also be 67xx cards (CEF or dCEF 720) .

Dual Active

In the worst case failure of a VSS (the link between the two switches goes down) we end up with a dual active situation. This is because the standby switch assumes the active has gone down and thus takes over.

Configuration

The configuration is summarised in to the following steps:

1. Configure the Virtual Switch Domain on both devices and designate each switch as either Switch 1 (primary) or Switch 2 (secondary)


2. (Optional) Configure switch priority settings


3. Configure the virtual switch links


4. Run the conversion (causing switches to reload)


5. Reconfigure the standby switches VSL on the active switch to complete configuration

Configuring the Virtual Switch Domain

The Virtual Switch Domain defines the grouping for the switches within the VSS system. The domain itself is an ID between 1 and 255 and should be unique for its layer 2 domain.

On Switch 1:

router-1# conf trouter-1(config)# switch virtual domain

router-1(config-vs-domain)# switch 1

On Switch 2:

router-2# conf trouter-2(config)# switch virtual domain

router-2(config-vs-domain)# switch 2

Configuring Switch Priorities (Optional)

VSS priorities are similar in nature to HSRP priorities. The highest priority node will assume to be active and the lowest standby. Both switches must have the same priority configuration settings to form a VSS system. By default, switch 1 will assume active (primary) and switch 2 will assume it is secondary.

To make switch 2 the primary switch, do the following on both switches:

router(config-vs-domain)# switch 1 priority 100

router(config-vs-domain)# switch 2 priority 110

Configure the Virtual Switching Link

The VSL link is a special link that carries control plane data between the two chassis. This must be configured on a 10GE port from either the Sup720-10GE or a 6708 line card.

In a deployment scenario the individual interfaces will differ. This article assumes the supervisor ports will be used to create the VSL link.

On Switch 1:

router-1(config)# interface port-channel 1

router-1(config-if)# no shut

router-1(config-if)# switch virtual link 1

router-1(config-if)# exit

router-1(config)# interface range tenGigabitEthernet 1/4 - 5

router-1(config-if-range)# no shut

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

router-1(config-if-range)# end

On Switch 2:

router-2(config)# interface port-channel 2

router-2(config-if)# no shut

router-2(config-if)# switch virtual link 2

router-2(config-if)# exit

router-2(config)# interface range tenGigabitEthernet 1/4 - 5

router-2(config-if-range)# no shut

router-2(config-if-range)# channel-group 2 mode on

router-2(config-if-range)# end

Executing the Conversion

This step creates a VSS system. This will convert all interface names in to a three mode notation, chassis/slot/port. Executing this mode will require a reload to merge both switches configurations, renumber all ports and to negotiation NSF/SSO etc between chassis and supervisors.
On both switches, issue:

router# switch convert mode virtual

You should select "yes" to reload the switch.

Finalising the Conversion

The conversion must be finalised by reconfiguring the port channel on the secondary switch.

On the active switch (probably Switch 1 unless you have set priority) enter the following:

router(config)# interface port-channel 2

router(config-if)# no shutrouter(config-if)# switch virtual link 2

router(config-if)# exit

router(config)# interface range tenGigabitEthernet 2/1/4 - 5

router(config-if)# channel-group 2 mode on

router(config-if)# no shut

router(config-if)# end

The system should now be a virtual switch! At this point, you should save your config and verify the system.

You can do this via the show switch virtual command.

router# sh switch virtual

Switch mode : Virtual Switch

Local switch number : 1

Local switch operational role: Virtual Switch Active

Peer switch number : 2

Peer switch operational role : Virtual Switch Standby