Cisco 6500 VSS Configuration Example

(Kesav A) #32

Hi Rene,

I’ve been going through your other posts and it’s really great. Also i was searching for VPC related links in google and it ended up 404 page.

Can you share me new links where i can go through regarding VPC member ports, peer link and traffic flow with an example ?

(Lazaros Agapides) #33

Hello Kesav!

I’ll try to answer your questions one by one below:

a) Why two virtual links need to be created? Is it that one virtual link is used for data traffic and one for management traffic? What is the benefit / use case of having two virtual links?

Actually, Rene has created only one virtual link and one port channel. It just happens that he named the port channel on SW1-VSS Po1 and the port channel on SW2-VSS Po2. They’re just two ends of the same set of physical links that form the port channel. The same occurs for the Virtual link. The end of the link on SW1 is called virtual link 1 and the other end of the same virtual link on SW2 is called virtual link 2.

b) Also you had responded to Ali’s question that we can use single port channel (Po12) and bind all interfaces in both the switches under this Po12. If so, can we have two virtual links binded under one Po12?

Rene clarifies this in his answer. The labels “1” and “2” can be anything on each end of the etherchannel (or of the virtual link for that matter). He suggested using Po12 on both ends. You can use whatever you like. If it makes more sense to you, use the same number on both ends.

c) Does the VSL link need to be trunk ? If it’s access port, how can it differentiate data traffic from multiple VLAN’s and management traffic?

This is a very good question. Actually, the answer is “it depends on the platform being used.” The good thing is however, that when you issue the switch virtual link command, the proper configuration for the platform is implemented, so you don’t actually have to configure the corresponding switchport command. For more information, check out this Cisco Support Community post:

d) Does VSL link have to be only L2? Can we have L3 interface as well for VSL?

Again, this is automatically configured by the switch virtual link command. See the following quote from the above link:

The 4500x works as switchportand the 6800 works only as no switchport.

e) There is no configuration mentioned regarding SSO? Do we have to configure SSO mode under redundancy or is that setup by default ?

SSO is not something you need to configure, it is the technology, or the method by which the VSL will operate when/if the active switch goes down.

f) Finally, do you have any reference post in your forum for understanding Quad SUP SSO feature & In – Chassis redundancy?

As far as I know, Quad SUP SSO is not yet included in the forum, but we’re working on it! In the meantime, you can take a look at this Cisco reference:

I hope this has been helpful!



Hi Rene

I am looking for Nexu material on this site but could not find the course link. Can you please help me with finding the course material for Nexus.
Do you have tips for how to practically do labs for Nexus, like GNS3 lab or do you have to any virtual lab specific to Nexus?


(Rene Molenaar) #35

Hi Palani,

Right now we don’t have any Nexus material. This is something I’d like to add in the future.

It’s difficult to do Nexus labs at the moment. Cisco VIRL has NX-OS but it only supports L3 features, not all the awesome L2 stuff that you want to learn. Nexus equipment is expensive to buy.

Cisco does have some resources however that you might be able to use:
Cisco PEC (Partned Education) Gold Labs



Thanks, Rene!.

(arun v) #37

@Rene- Does this procedure is same for 6800 series switches ?

(Lazaros Agapides) #38

Hello Arun.

I have never implemented VSS myself on a 6800 series switch but based on my research, as long as you have a Supervisor 2T that supports VSS and the proper IOS, you can configure VSS in the same manner on both the 6500 and the 6800.

I hope this has been helpful!


(Shantel - split this topic #39

19 posts were merged into an existing topic: Cisco 6500 VSS Configuration Example

(sims) #40


Rene If a switch is connected to VSS enable switch ( redundant connectivity switch 1 and switch 2 ) and RSTP is running in this case
who will be the root bridge ?


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(Abhishek D) #41

Hi team

what is the dual-active detection concept ?
To achieve dual active detection - do we need to have separate link between both VSS chassis OR it is part of VSL ?


(Rene Molenaar) #42

Hi Abhishek,

If your VSL fails then the standby switch can’t tell if the active switch is still there or not. If the standby switch goes active while the active switch is still there, both will be active, forwarding packets and you’ll run into issues. This is called “dual active”.

Dual-active detection is configured outside of the VSL link. There’s enhanced PAgp, BFD and Dual-Active Fast Hello Packets to use. You can use one or all three at the same time.

Cisco has a pretty good document for this:


(Shantel - split this topic #43

19 posts were merged into an existing topic: Cisco 6500 VSS Configuration Example

(Helen N) #44

Is it necessary to use a port channel to configure vss?

I currently only have 2 sfps to connect two
4506-E switches

(Lazaros Agapides) #45

Hello Helen

The use of two or more links for the Virtual Switch Link (VSL) is only a recommendation by Cisco. It is not manditory. However, this is not recommended as VSS is designed to be a high availability system and by having only one link, this high availability is sacrificed. It should be implemented fully realising this. Ideally, you should purchase an additional module to implemente multiple links.

I hope this has been helpful!


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(Jason F) #46

I’m sure I’m missing something here but if I were to use VSS on 2 layer 3 4500 chassis and wanted to connect a access switch to the VSS pair would I use a regular port channel to connect to the VSS pair from the access switch or is there an actual multi-chassis Ethernet port configuration I would need to configure between the access switch and the VSS pair? I’m just a bit confused as to what configuration I need to connect multiple access layer switches to the VSS pair. I’ve been trying to research it but am pretty confused about the topic as I’m not able to see a straight forward answer. Any clarification would be helpful.

(Lazaros Agapides) #47

Hello Jason

There is no special configuration that you need to apply to the access switch that connects via etherchannel to the VSS pair. From the point of view of the access switch, the etherchannel that is being configured would be exactly the same whether both (or all) links are connected to the same physical switch or if they are connected to both members of the VSS pair. The special configuration would be applied on the VSS pair side.

Take a look at the following Cisco documentation that describes such a configuration:

I hope this has been helpful!


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(Inon L) #48

Hey, you mentioned that NSF and SSO don’t have to be configured but Cisco documentation says otherwise: “Configure SSO and NSF on each chassis”

Do I miss something here, or it’s something new that you aren’t familiar with?

(Lazaros Agapides) #49

Hello Inon

Yes, you are correct that according to Cisco documentation, both SSO and NSF are necessary in order for VSS to function. Rene doesn’t mention in the lesson that they don’t have to be configured, but mentions them as features and explains what they do. In any case, I will ask Rene to take a look and to make any clarifications necessary to the lesson to avoid confusion.

Thanks for bringing this up!


(Justin A) #50

In the VSS lesson there was a mention that not all ports are compatible for VSL, is there a reason for this? If anyone has an explanation or an article that I can read I would be very grateful.

(Lazaros Agapides) #51

Hello Justin

VSS requires that VSLs are configured on 10Gbps ports only. Not only this, but these ports must either be on the supervisor itself or on one of several switching modules. You can find more info about this at the following Cisco documentation:

Look at the section titled “VSL Hardware Requirements”.

Now the reason that only specific ports can be used is because the requirements of the VSL are very specific. A VSL link has the following characteristics:

  • The VSL gives control traffic higher priority than data traffic so that control messages are never discarded.
  • When a VSL is configured, all existing configurations are removed from the interface except for specific allowed commands
  • When VSL is configured, the system puts the interface into a restricted mode. This means that only specific configuration commands can be configured on the interface.

All of these restrictions and limitations are there in order to ensure that the link created between the two switches is sufficient to provide the necessary communication for VSS to function.

I hope this has been helpful!


Ethernet port can be
located on the supervisor engine module or on one of the following switching modules:
• WS-X6708-10G-3C or WS-X6708-10G-3CXL
• WS-X6716-10G-3C or WS-X6716-10G-3CXL
• WS-X6716-10T-3C or WS-X6716-10T-3CXL

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