As part of a network infrastructure upgrade at a client site, I’ll be implementing Cisco VSS (Virtual Switching System). This technology will go a long way to meet some of the stated objectives of this infrastructure upgrade which include : Physical Hardware Redundancy, High Availability achieved by Switch Clustering, Self-healing, Increased bandwidth (10 GB trunk), to mention a few.

Quick Background on VSS:
A Virtual switching system (VSS) combines a pair of Catalyst 4500X series switches into a single network component, enabling them to function as one logical switch.Cisco Virtual Switching System is a clustering technology that pools two Cisco Catalyst 4500X Series Switches into a single virtual switch.

In a VSS, the data plane of both clustered switches is active at the same time in both chassis. In my VSS implementation, both VSS Switch members are connected by 2 virtual switch links (VSLs) using 10 Gigabit Ethernet connections between the VSS members. Virtual Switch Links carry regular user traffic in addition to control data between the VSS members.

Prerequisites:

I have outlined my VSS configuration steps for a pair of Cisco Catalyst 4500X switches below starting with Switch-1. The following diagram illustrates the physical topology:

Switch 1 Virtual Domain and Port Channel Configuration:

Switch-1(config)#switch virtual domain 100

Switch-1#switch convert mode virtual (Execute the command, but do not reload until VSS configuration is completed on Switch 2)

Switch 2 Virtual Domain and Port Channel Configuration:

Switch-2(config)#switch virtual domain 100

Switch-2#switch convert mode virtual

At this point, console into Switch-1 . You will be prompted to save the work and confirm the switch reboot. Do the same for Switch-2.

After the reboot, verify the VSS configuration:

Switch-1#sh switch virtual

Pagp dual-active detection enabled: Yes
FastHello dual-active detection enabled: Yes
In dual-active recovery mode: No

After the VSS configuration and restart, both switches start to function as one. One switch is designated as the Active and the other as the Standby switch. If I attempt to console into the Standby switch and run commands, I get the following prompt:

Switch-1-Standy#sh run
Standby console disabled.
Valid commands are: exit, logout

Configure VSS Cluster Uplink to Distribution Stack Switches as Multichassis EtherChannel (MEC):

VSS enables the creation of Multi-Chassis EtherChannel (MEC), which is an Etherchannel whose member ports are distributed across the member switches in a VSS. The fact that ports from both chassis of the Virtual Switching System are included in this etherchannel makes it a Multichassis EtherChannel (MEC). My MEC configuration steps are below.

Console into the VSS switch cluster. Doesn’t matter if it’s the Switch master or slave, and configure the etherchannel switchport as it would on any other switch(In this scenario, I’m consoled into the standby/slave switch):

Switch-1(config)#interface port-channel 30
Switch-1(config)#switchport
Switch-1(config)# no shut

Add ports from both chassis of the VSS Cluster to the Port Channel:

Switch-1(config)#interface range tenGigabitEthernet 1/1/3, tenGigabitEthernet 2/1/3
Switch-1(config-if)#switchport channel-group 30 mode on
Switch-1(config-if)#no shut

Configure the port channel and the physical ports in the Upstream Distribution Stack Switch:

DataCenterStack(config)#interface port-channel 30
DataCenterStack(config-if)#switchport trunk encapsulation dot1q
DataCenterStack(config-if)#switchport mode trunk
DataCenterStack(config-if)#no shut

Add the Stack switches physical ports to the Channel group. This would be the ports fitted with the X2-10GB-SR fiber converters on the Distribution Layer 3750E-48PD switches as indicated in the diagram above:

DataCenterStack(config)#interface range TenGigabitEthernet1/0/1-2
DataCenterStack(config-if)#switchport trunk encapsulation dot1q
DataCenterStack(config-if)#switchport mode trunk
DataCenterStack(config-if)#channel-group 30 mode on
DataCenterStack(config-if)#exit
DataCenterStack(config)#

Verify Ether Channel configuration :

DataCenterStack#sh etherchannel summary
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator

I configured an SVI (Switch Virtual Interface) for telnet or ssh(preferably) management. I would add that it’s important to verify that the version of Cisco IOS-XE software on both VSS switches is the same.