VSS: PART 1: VSS BASICS, VSS CONFIGURATION


TOPICS

VSS BACKGROUND

TRADITIONAL NETWORK vs VSS NETWORK

UNDERSTANDING VSS CLI

VSS CONFIGURATION

REFERENCE LINKS


 

VSS BACKGROUND

In case of redundant devices, there are actually quite a few solutions that can be used.

We have HSRP & VRRP available as the redundancy protocol. These first-hop redundancy protocols are usually heavily tied to a fast-converging routing protocol like EIGRP, and still require that each device maintain its own control plane.

In simple words, two switches are actually acting as separate switches in terms of processing. One switch will act as Active & one as Standby.

Often, two switches are configured, and one responds to ARP requests while the other does not. This is an active/passive relationship.

VSS goes one step ahead to all of these.

VSS merges the two switches into one virtual “mega-switch”, rather than wasting a perfectly good switch.

There’s still a master/slave relationship, but rather than placing one switch in standby while the other is active, this determines which switch maintains control over the other

The function of the supervisor module, as well as the configuration of both switches, becomes the responsibility of the primary switch.


 

TRADITIONAL NETWORK  vs  VSS NETWORK

 

prod qas0900aecd806ed74b 1 Virtual Switching System (VSS) on Cisco Catalyst 6500

 

In either case, these two switches are configured with a port channel between them. Using HSRP, you can establish redundancy just fine, but keep in mind that since both switches are distinct entities, you must rely on spanning tree to eliminate bridging loops, which means each access layer switch will put one of their uplink connections to the core in a blocking state.

VSS utilizes the port channel between the switches to merge them together into one massive switch. As a result, redundant connections from the Access layer to the Core no longer need to be blocked because since they’re virtually both connected to the same switch, they can be configured in a port-channel, as shown by the diagram to the right.


 

UNDERSTANDING VSS CLI

Both the switches are virtually & merged, which looks like a single switch in their functionality.

Switch ports naming convention: This configuration also adds a third number to the interface names, which looks like Chassis/Slot/Port.

 

Example: GigabitEthernet 2/1/1

It is signifying Switch number 2 / Line card 1 / Port number 1    Or,

First port on the first card on switch 2

 

We cannot enter into global configuration mode on the secondary switch

6509SW1-sdby#conf t

Standby console disabled


 

VSS CONFIGURATION

CONFIGURE REDUNDANCY MODE

6509SW1(config)# redundancy

6509SW1(config-red)# mode sso

SSO: Stateful Switch Over. With SSO redundancy, the VSS standby supervisor engine is always ready to assume control following a fault on the VSS active supervisor engine.

VSS operates with SSO, if following conditions are met

  • Both supervisor engines must be running the same software version.
  • VSL-related configuration in the two chassis must match.
  • PFC mode must match.
  • SSO and nonstop forwarding (NSF) must be configured on each chassis.

 

BASIC / STANDARD CONFIGURATION

6509SW1(config)# switch virtual domain 100

6509SW1(config-vs-domain)# switch 1

6509SW1(config-vs-domain)# switch mode virtual

6509SW1(config-vs-domain)# switch 1 priority 1106509SW1(config-vs-domain)# switch 2 priority 100

6509SW2(config)# switch virtual domain 100

6509SW2(config-vs-domain)# switch 2

6509SW2(config-vs-domain)# switch mode virtual

6509SW2(config-vs-domain)# switch 1 priority 110

6509SW2(config-vs-domain)# switch 2 priority 100

The priority configuration shown above is optional, and will produce the same results as is the default, since in the event of a priority tie, the smaller numbered switch will be elected the primary, but it is important to remember that the configurations must be identical to form a VSS system.

 

CONFIGURE PORT CHANNEL BETWEEN VSS SWITCHES

6590SW1(config)# interface port-channel 1

6509SW1(config-if)# no shut

6509SW1(config-if)# switch virtual link 1

6509SW1(config-if)# interface range TenGigabitEthernet 1/1 – 2

6509SW1(config-if-range)# no shut

6509SW1(config-if-range)# channel-group 1 mode on

6509SW2(config)# interface port-channel 2

6509SW2(config-if)# no shut

6509SW2(config-if)# switch virtual link 2

6509SW2(config-if)# interface range TenGigabitEthernet 1/1 – 2

6509SW2(config-if-range)# no shut

6509SW2(config-if-range)# channel-group 2 mode on

 

FINAL STEP ON BOTH THE SWITCHES

6509SW1# switch convert mode virtual

It should ask you to reload, select yes. The switches will come back up as a VSS pair, and the interfaces on the secondary switch will be assimilated into the configuration for the primary switch

 

VERIFY VSS DETAILS

6509SW1#show switch virtual

Switch mode : Virtual Switch

Virtual switch domain number : 100

Local switch number : 1

Local switch operational role: Virtual Switch Active

Peer switch number : 2

Peer switch operational role : Virtual Switch Standby


REFERENCE LINKS

TOPIC: Virtual Switching System (VSS) on Cisco Catalyst 6500

WEBSITE: KEEPING IT CLASSLESS

http://keepingitclassless.net/2011/10/virtual-switching-system-on-cisco-catalyst-6500/

 

TOPIC: VSS

WEBSITE: CISCO

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12-2SX/configuration/guide/book/vss.html#wp1054565

 

TOPIC: VSS FAQ

WEBSITE: CISCO

http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-6500-virtual-switching-system-1440/prod_qas0900aecd806ed74b.html


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