Virtual Switching System

 

VSS Overview

The Cisco VSS simplifies network configuration and operation by providing a loop-free Layer 2 topology using two Catalyst 6500 switches acting as one big Virtual switch. VSS reduces number of Layer 3 routing neighbors by providing a Layer 2 connectivity for access/distribution switches.

A VSS is a pair of combined 6500 switches acting as a single network element with redundancy and load balancing over port-channels (etherchannels). One switch becomes the master or active chassis and the other one becomes the VSS standby.

 

VSS Switch Roles

• VSS Active: The active chassis controls the VSS operation. It runs the control plane, L2 and L3 control protocols. It also runs the management plane functions like console interface, logs, file system and even power management.
• VSS Standby: Listens to master, checks the status, forwards the ingress traffic but sends all control traffic to the VSS active chassis for processing.

Virtual Switch Link

To share control and data traffic between two chassis a VSL – Virtual Switch Link is required. VSL is implemented as a Port Channel. The control traffic gets higher priority over data on a VSL and never gets discarded.

 

before configuration make sure that you have right IOS image, proper VS-capable supervisor and line cards, you can check your line cards with the following command:

6500A#switch convert check vss-capable
This is a VSS capable switch.
VSL ports can be configured in slot: 4, 5, 6

 

VSS Configuration

By default, 6500 series switches are configured to operate in standalone mode. The following steps are required in order to setup virtual stack across two 6500 chassis.

Step1: Make sure SSO and NSF are configured and enabled

Step2: Assign Virtual Switch Doman and Switch numbers

Step3: Configure VSL Port Channel, PO# should be unique on each chassis.

Step4: Convert Standalone Chassis to Virtual Switch mode

Step1:

6500A(config)#redundancy
6500A(config-red)#mode sso
!

Step2:

6500A(config)#switch virtual domain ?
  <1-255>  Virtual switch domain number

6500A(config)#switch virtual domain 100
Domain ID 100 config will take effect only
after the exec command 'switch convert mode virtual' is issued

6500A(config-vs-domain)#switch 1
6500A(config-vs-domain)#exit

...

6500B(config)#switch virtual domain 100
Domain ID 100 config will take effect only
after the exec command 'switch convert mode virtual' is issued

6500B(config-vs-domain)#switch 2
6500B(config-vs-domain)#exit

Step3:

6500A(config)#int port-channel 100
6500A(config-if)#switch virtual link 1
6500A(config-if)#no shutdown
6500A(config-if)#exit
6500A(config)#int te5/4
6500A(config-if)#channel-group 100 mode on
6500A(config-if)#no shutdown
6500A(config)#int te6/4
6500A(config-if)#channel-group 100 mode on
6500A(config-if)#no shutdown

...

6500B(config)#int port-channel 200
6500B(config-if)#switch virtual link 2
6500B(config-if)#no shutdown
6500B(config-if)#exit
6500B(config)#int te5/4
6500B(config-if)#channel-group 200 mode on
6500B(config-if)#no shutdown
6500B(config)#int te6/4
6500B(config-if)#channel-group 200 mode on
6500B(config-if)#no shutdown

Step4:

6500A#switch convert ?
  check  check if this switch and its modules are VSS capable or not
  mode   mode keyword virtual or standalone

6500A#switch convert mode ?
  stand-alone  stand-alone switch
  virtual      virtual switch

6500A#switch convert mode virtual

This command will convert all interface names
to naming convention "interface-type switch-number/slot/port",
save the running config to startup-config and
reload the switch.

NOTE: Make sure to configure one or more dual-active detection methods
once the conversion is complete and the switches have come up in VSS mode.

Do you want to proceed? [yes/no]: yes
Converting interface names
Building configuration...
Saving converted configuration to bootflash: ...
Destination filename [startup-config.converted_vs-20110705-214318]?

*** --- SHUTDOWN NOW ---

 

Ensure that same PFC operating mode is being used on both chassis in order to have a proper SSO redundancy mode:

6500A#show platform hardware pfc mode
PFC operating mode : PFC3C

Now, Let’s look at configuration of VSS switch after reboot:

6500A#sh run
…
!
hostname 6500A
!        
switch virtual domain 100
switch mode virtual
!        
mls netflow interface
mls cef error action reset
!
spanning-tree mode pvst
spanning-tree extend system-id
diagnostic bootup level minimal
!        
redundancy
main-cpu
  auto-sync running-config
mode sso
!
vlan internal allocation policy ascending
vlan access-log ratelimit 2000
!
!
interface Port-channel100
no switchport
no ip address
switch virtual link 1
mls qos trust cos
no mls qos channel-consistency
!
interface Port-channel200
no switchport
no ip address
switch virtual link 2
mls qos trust cos
no mls qos channel-consistency
!        
interface GigabitEthernet1/1/1
no switchport
no ip address
shutdown
!        
interface GigabitEthernet1/1/2
no switchport
no ip address
shutdown
...
...
interface TenGigabitEthernet1/5/4
no switchport
no ip address
mls qos trust cos
channel-group 100 mode on
...
...
interface TenGigabitEthernet1/6/4
no switchport
no ip address
mls qos trust cos
channel-group 100 mode on
...
...
interface TenGigabitEthernet2/5/4
no switchport
no ip address
mls qos trust cos
channel-group 200 mode on
...
...
interface TenGigabitEthernet2/6/4
no switchport
no ip address
mls qos trust cos
channel-group 200 mode on
...
...
interface Vlan1
no ip address
shutdown
!
ip classless
ip forward-protocol nd
!
control-plane
!
line con 0
line vty 0 4
login
!
mac-address-table aging-time 480
no event manager policy Mandatory.go_switchbus.tcl type system    
!
module provision switch 1
slot 1 slot-type 147 port-type 61 number 48  virtual-slot 17
slot 3 slot-type 152 port-type 31 number 48  virtual-slot 19
slot 4 slot-type 227 port-type 60 number 8  virtual-slot 20
slot 5 slot-type 254 port-type 31 number 2 port-type 61 number 1 port-type 60 number 2  virtual-slot 21
slot 6 slot-type 254 port-type 31 number 2 port-type 61 number 1 port-type 60 number 2  virtual-slot 22
!
module provision switch 2
slot 1 slot-type 147 port-type 61 number 48  virtual-slot 33
slot 3 slot-type 152 port-type 31 number 48  virtual-slot 35
slot 4 slot-type 227 port-type 60 number 8  virtual-slot 36
slot 5 slot-type 254 port-type 31 number 2 port-type 61 number 1 port-type 60 number 2  virtual-slot 37
slot 6 slot-type 254 port-type 31 number 2 port-type 61 number 1 port-type 60 number 2  virtual-slot 38
!
end

Verification:

Verification is the most important part of configuration, you need to make sure that commands that you have entered are working as expected!

6500A#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

6500A#show switch virtual role

Switch  Switch Status  Preempt    Priority  Role     Session ID
        Number         Oper(Conf) Oper(Conf)         Local  Remote
------------------------------------------------------------------
LOCAL    1     UP      FALSE(N )   100(100)  ACTIVE   0      0  
REMOTE   2     UP      FALSE(N )   100(100)  STANDBY  4004   1462
In dual-active recovery mode: No

6500A#show switch virtual link
VSL Status : UP
VSL Uptime : 43 minutes
VSL SCP Ping : Pass
VSL ICC Ping : Pass
VSL Control Link : Te1/5/4 

6500A#show switch virtual link port-channel
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      N - not in use, no aggregation
        f - failed to allocate aggregator

        M - not in use, no aggregation due to minimum links not met
        m - not in use, port not aggregated due to minimum links not met
        u - unsuitable for bundling
        d - default port

        w - waiting to be aggregated
 
Group  Port-channel  Protocol    Ports
------+-------------+-----------+-------------------
100    Po100(RU)        -        Te1/5/4(P)     Te1/6/4(P)    
200    Po200(RU)        -        Te2/5/4(P)     Te2/6/4(P)

If I connect my console to secondary chassis:

6500A-sdby>
Standby console disabled

 

Multi-Chassis EtherChannel

One VSS supports a maximum of 512 - 2 port channels (deducting 2 POs for VSL) Configuration of MEC is not different than any regular etherchannel! The Different is physical connectivity, one link connects to VSS Active and the other link connects to VSS Standby chassis creating a high bandwidth active/active aggregated link-bundle (Etherchannel)

Access switch:

interface GigabitEthernet1/1/1
channel-group 10 mode on
!
interface GigabitEthernet1/1/2
channel-group 10 mode on

Core switch:

interface Port-channel10
switchport
!
interface GigabitEthernet1/3/17
switchport
channel-group 10 mode on
!
interface GigabitEthernet2/3/17
switchport
channel-group 10 mode on

Verify:

6500A#sh etherchannel summary
Number of channel-groups in use: 3
Number of aggregators:           3

Group  Port-channel  Protocol    Ports
------+-------------+-----------+--------------------------------------
10     Po10(SU)         -        Gi1/3/17(P)    Gi2/3/17(P)   
100    Po100(RU)        -        Te1/5/4(P)     Te1/6/4(P)    
200    Po200(RU)        -        Te2/5/4(P)     Te2/6/4(P)    

 

Switch12#sh etherchannel summary
Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+--------------------------------------
10     Po10(SU)         -        Gi1/1/1(P)  Gi1/1/2(P)