VSS - basics

Some time ago I had opportunity to configure two Cisco 4500x devices to work in VSS (Virtual Switching System).

I decided to make short documentation from that experience for future reference.

VSS allows for combining two physical devices into one logical system.

VSS devices are connected through VSL - (Virtual Switch Link, port-channel on each switch).

One of the benefits which can be used when VSS is in place - is MEC (Mutlichassis EtherChannel).

Using MEC - we can for example connect other network device or server to both switches (switch1 and switch2 - which are configured in VSS) and configure this link as EtherChannel.

Configuration presented in this post will result in :
1. Basic VSS configuration for two Cisco 4500x devices.
2. Dual active detection configured (using Fast Hello mechanism). Prevent from both switches being Active in situation when VSL fails.

On Diagram 1 setup which will be used for that article is presented.

Majority of configuraton will be done on switch1 and switch2 independently (to configre VSS).
At the moment when VSS is operational - commands will be executed in VSS.

Steps:
1. Preparing the configuration on switch1 and switch2
2. Convert switch1 and switch2 to virtual mode
3. Configure Dual Active Detection

Step 1:
[switch1]
switch virtual domain 10
 switch 1

Note: port-channel number is different than on switch2
interface port-channel 10
switchport
switch virtual link 1
no shutdown

interface TenGigabitEthernet1/2
channel-group 10 mode on

interface TenGigabitEthernet1/3
channel-group 10 mode on

[switch2]
switch virtual domain 10
 switch 2

Note: port-channel number is different than on switch1
interface port-channel 20
switchport
switch virtual link 2
no shutdown

interface TenGigabitEthernet1/2
channel-group 20 mode on

interface TenGigabitEthernet1/3
channel-group 20 mode on

Step 2:
[switch1]
switch convert mode virtual

[switch2]
switch convert mode virtual

Step 3:
[VSS]

Note: Dual active detection should be enabled in virtual domain by default (step present to show the command).
switch virtual domain 10
 dual-active-detection fast-hello

Note: interface numbers now contain switch number (switch/module/port)
interface TenGigabitEthernet1/1/5
dual-active fast-hello
no shutdown

interface TenGigabitEthernet2/1/5
dual-active fast-hello
no shutdown


Relevant show commands:
show switch virtual
show switch virtual role
show switch virtual link
show switch virtual link port-channel
show switch virtual dual-active summary