VPC failover

[Amr Hafez]

Dear All

I have 2 Nexus SW 7706 with 1 SUP-2E in each SW

If I configured VPC between both SWs 

If SUP in one of them go down does the performance affected ?

as I knew that VPC make both SWs individual in management but appear as one SW to down stream devices (not like VSS where both SWs appear as one SW in management and one SW to the down stream devices)

and are there another technologies in Nexus to be such VSS except VPC ?

thanks in advance  

[InayathUlla Sharieff]

Hi Amr,

VSS vs VPC (difference between VSS and vPC)

I know many of you have been looking for an answer to this question "what are the differences between VSS and vPC? "..here are the differences  between VPC and VSS in a very easy way, You just need to read it once..

Both are used basically to support multi-chassis ether-channel that means we can create a port-channel whose one end is device A,however, another end is physically connected to 2 different physical switches which logically appears to be one switch.

There are certain differences as listed below:

-vPC is Nexus switch specific feature,however,VSS is created using 6500 series switches

-Once switches are configured in VSS, they get merged logicaly and become one logical switch from control plane point of view that means single control plane is controlling both the switches in active standby manner  ,however, when we put nexus switches into vPC, their control plane are still separate. Both devices are controlled individually by their respective SUP and they are loosely coupled with each other.
 

-In VSS, only one logical switch has be managed from management and configuration point of view. That means, when the switches are put into VSS, now, there is only one IP which is used to access the switch. They are not managed as separate switches and all configuration are done on active switch. They are managed similar to what we do in stack in 3750 switches,however, in vPC, the switches are managed separately. That means both switches will have separate IP by which they can be accessed,monitored and managed. Virtually they will appear a single logical switch from port-channel point of view only to downstream devices.
-As i said, VSS is single management and single configuration, we can not use them for HSRP active and standby purpose because they are no longer 2 seperate boxes. Infact HSRP is not needed, right?
one single IP can be given to L3 interface and that can be used as gateway for the devices in that particular vlan and we will still have redundancy as being same ip assigned on a group of 2 switches. If one switch fails, another can take over.,however, in vPC as i mentioned above devices are separately configured and managed, we need to configure gateway redundancy same as in traditional manner.

For example: We have 2 switches in above diagram. Switch A and B, when we put them in VSS, they will be accessed by a single logical name say X and if all are Gig ports then interfaces will be seen as GigA\0\1, GigA\0\2....GigB\0\1,GigB\0\2 and so on...
however,if these are configured in vPC, then they will NOT be accessed with single logical name. They will be accessed/managed separately. Means, switch A will have its own port only and so on B.

-Similary, in VSS same instances of stp,fhrp,igp,bgp etc will be used,however, in vPC there will be separate control plane instances for stp,fhrp,igp,bgp just like they are being used in two different switches

-in VSS, the switches are always primary and secondary in all aspects and one switch will work as active and another as standby,however, in vPC they will be elected as primary and secondary from virtual port-channel point of view and for all other things,they work individualy and their role of being primary/secondary regarding vpc is also not  true active standby scenario,however, it is for some particular failure situation only. For example, if peer-link goes down in vpc, then only secondary switch will act and bring down vpc for all its member ports.

-VSS can support L3 port-channels across multiple chassis,however, vpc is used for L2 port-channels only.

-VSS supports both PAgP and LACP,however, VPC only supports LACP.

-In VSS, Control messages and Data frames flow between active and standby via VSL,however, in VPC,Control messages are carried by CFS over Peer Link and a Peer keepalive link is used to check heartbeats and detect dual-active condition.

Hope this answers your query.

Regards

Inayath

[Amr Hafez]

Thanks Inayath

I knew in VSS if one SUP go down standby SUP take the operation of primary SUP to control and manage both SWs 

but in vPC if both SUP are active and separate in control plane so SUP1 manage NX-SW 1 and SUP2 manage NX-SW 2 and both appeared as one single SW to down stream device  but one of them is primary SW and other is secondary

so if SUP1 go done does the data and control plane go down or  the control plane only go down but data plane still work what happens? 

and are there another technology to do VSS or stacking in NX-SW?

[InayathUlla Sharieff]

In Nexus when you have VPC configured:-

1- Sup goes down, the standby take over the active role and start to send the traffic.

{

Failure Reaction: One vPC Peer Switch Failure

If a vPC peer switch the other remaining vPC switch will keep forwarding data. All traffic now moves via this remaining switch and this definitely results in limited bandwidth but does not affect the end point reachability or any services running. In case there was heavy over-subscription of the link, then this may cause some issue, like random traffic drops.

}

2) there is no stacking in Nexus Sw.

HTH

Regards

Inayath

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[Amr Hafez]

may be my message misunderstood

1- i have only one SUP per NX-SW not two SUPs and one of them is active, other standby

2- I mean  I have two NX-SWs with one SUP in each and configured as vPC domain and both are separate in management and control plane so if SUP in NX-SW 1 go down what will this SW do with data plane and control plane as you mention that each SW has it's own control and management plane? so NX-SW 2 could not control and manage NX-SW1 with the failed SUP ?

[InayathUlla Sharieff]

The current packet flow used by the active will be lost. All the new traffic will be flown through the second switch.

[Amr Hafez]

so VSS is better than vPC because in vss the traffic load balancing in both SWs and if the active SUP go down the other SUP in the second SW  can controll both SWs

but in vPC if SUP of any SW become down (if I use only one SUP/SW) the entire SW could not forward traffic and I will use only one SW not such catalyst VSS

thanks alot

but if all your information is correct, I think vPC need more improvement or Cisco have to enable stacking or any technology acts as VSS in catalyst