VSS Deploymnet / NSF

Unanswered Question
Sep 21st, 2009

We are planning to implement the VSS on our data center core switch.

At present we are having only one 6509 switch with 2 supervisors…

I am planning to use standby supervisor of live 6509 chassis in to another 6509 chassis (Both chassis are compatible to VSS )

Have following query.

1. For NSF configuring routing protocol is necessary /mandate step

2. As of now only 1 6509 chassis is live & uplinked to access switches (Simple L2 uplinks & static routes toward Copr Firewall). Will be placing another chassis to form VSS….but am not clear from where to start…..Should I start from live chassis or standby one….

Can someone please guide sequence or steps I should follow-up.

Thanks In Advance..

Yogesh Suryawanshi


I have this problem too.
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Giuseppe Larosa Mon, 09/21/2009 - 02:18

Hello Yogesh,

you can remove the standby supervisor to prepare the second chassis.

Then you should configure and connect the VSL links.

I suggest to deploy also links for dual-active detection using BFD and fast hellos.





then when everything is ready you need to ask a maintanance window to perform the conversion.

Then later you can add L2 uplinks between the access layer switches and the standby chassis.

This should be a reasonable activity list.

Hope to help


yogesh.suryawanshi Mon, 09/21/2009 - 02:30

Thats gr8 Giuseppe,

Few more queries:

NSF configuration is Mandatory? If yes...does it requires routing protocols configurations?



Giuseppe Larosa Mon, 09/21/2009 - 10:45

Hello Yogesh,

NSF is recommended and logical on a VSS scenario.

NSF extensions are usually enabled by default on modern IOS images.

You can check this looking at

sh ip protocols

if you see a line like NSF aware this is good.

To be noted that VSS routing neighbors has to be NSF aware (able to assist the device during sup switchover) and the VSS has to be NSF capable to implement this correctly.

Hope to help


yogesh.suryawanshi Mon, 09/21/2009 - 23:59

Hello Giuseppe,

Really Appreciate your response to VSS queries & it has helped to make migrations steps & plan the migration.

I have few more queries on activity list you have advised...

#####you can remove the standby supervisor to prepare the second chassis.

Then you should configure and connect the VSL links. ###

Query 1.-- followng are the setps which i am plainng to take ....---please correct if i am wrong at any place..

---Step 1---Live Chassis---

Core-1(config)#switch virtual domain 100

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

Core-1(config-vs-domain)# exit

Core-1(config)#interface port-channel 100

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

Core-1(config-if)#interface TenG 5/4

Core-1(config-if)#channel-group 100 mode on

Core-1(config-if)#interface TenG 5/5

Core-1(config-if)#channel-group 100 mode on

Core-1(config-if)# ^Z


--Step 2 :2nd chassis --which is not live as of now

Core-2(config)#switch virtual domain 100

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

Core-2(config-vs-domain)# exit

Core-2(config)#interface port-channel 200

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

Core-2(config-if)#interface TenG 5/4

Core-2(config-if)#channel-group 200 mode on

Core-2(config-if)#interface TenG 5/5

Core-2(config-if)#channel-group 200 mode on

Core-1(config-if)# ^Z


---Step 3 : and then go for conversion on Core 1 (Which is Live as of now)

Core-1 (Config)# switch convert mode virtual

Core-1 (Config)# switch accept mode virtual

---Step 4 :after that Core 2 (Which is not live as of now)

Core-2 (Config)# switch convert mode virtual

Core-2 (Config)# switch accept mode virtual


Query 2 :

From above step wanted to make sure config of live box does not get override....

Query 3:

Live chassis active as server for VTP domain...anything will change after conversion / do we need to make any changes after conversion & also what will happen to Interface vlans which are configured as of now

Query 4 : After conversion can we configure Dual active detection or we have to confiugre while conversion



Giuseppe Larosa Tue, 09/22/2009 - 01:36

Hello Yogesh,


>> Then you should configure and connect the VSL links

I was meaning that you should configure the links in a standard way to verify their health with both chassis in standalone mode.

I would include on these links to be prepared the links for BFD/ fast hello dual active detection.

This can be a GE link because there is no strict need for 10GE for a simple IP BFD and/or fast hello.

All the other activity for setting up VSS should be performed during the maintanance window.

At the beginning of maintanance window I would isolate the two chassis.

You can configure a priority and preemption to make current chassis the master.

Isolate the two chassis or configure primary chassis first.

Configure both chassis for VSS as you have described with in addition the link for dual-active detection and the priorities and preemption.

Save configuration on both chassis.

Power off both chassis.

Power on master chassis first

Wait for the boot process to finish

Power on secondary chassis.

Use the following step-by-step document as a reference for your action plan.




it describes how to migrate two stand-alone distribution switches to VSS.

take care of step 10 accept vss

your questions:


configuring the primary switch with preempt +greater priority should help in keeping current config.

3) VTP config should be kept if you make sure that current chassis will be primary the first time the two chassis talk to each other.

4) I think it is better to plan for additional link before. I would leave for a second time the connection of access-layer switches to second chassis.

Hope to help



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