VLAN Pool sizing

[udo.konstantin]

Hi community, 

What is the basis for the size of the VLAN pool? I mean a VLAN is normally associated to one EPG when it is static assigned. For a VMM domain the assignment of VLANs is dynamic. I searched a lot of document bit didn't found a recommendation. The number of a dynamic VLAN for VMM domain seems always arbitrary. 

Thanks 

Udo 

[RedNectar]

Hi Udo,

I guess my previous answer (https://community.cisco.com/t5/application-centric/aci-vlan-pool-recommendations/m-p/3008721#M2426) didn't quite finish the job.  Here are a few more tips that might help you:

Static VLAN Pool Sizing

In traditional networking you are effectively working with a static pool of VLANs which includes VLANS 1-4095 all the time.

So if you want to emulate your existing situation, create all static pools with 4095 VLANs.  You see, with Static VLANs, YOU do the planning. YOU decide which VLAN goes where, just like you always have, with the added restriction that the VLAN ID you choose must exist in the VLAN Pool you are using.

If you already have a scheme that says "This range of VLANs is used for x and that range is used for y", then use that scheme to size yout VLAN Pools, otherwise, you could use VLAN pools with 4095 VLANs - even multiple pools with 4095 VLANs, because YOU decice which VLAN to use where, and if you use the same VLAN twice, then that's your fault.

But I'd advise not using a pool of 4095 VLANs, especially if you ever plan to use Dynamic VLANs.  It is easy to add MORE VLANs to a pool, but very hard to remove them.

Dynamic VLAN Pool Sizing

If you plan to use dynamic VLANs, then you should make sure that you have set aside some VLANs for dynamic allocation.  Again, remember, it is easy to add MORE VLANs to a pool, but very hard to remove them, so if your VMM Domain is planned to have 100 VMs, begin with a pool size of 100.

So your observation that

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The number of a dynamic VLAN for VMM domain seems always arbitrary. 

is absolutely correct, it is just as arbitary as the number of VMs that you expect to have in yout VMM Domain.

My advice:

1. Set aside as many VLANs as you can for dynamic allocation. Don't use these VLANs in static allocations, but that's up to you to enforce.
2. From this range, assign a smallish number for your VMM Domain - say 50% larger than your current requirement.
3. Add more VLANs to the pool as needed.

I hope this helps.

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Don't forget to mark answers as correct if it solves your problem. This helps others find the correct answer if they search for the same problem

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[udo.konstantin]

Hi Chris,

once again your answer is great and yes you are right, your last answer didn't finish the job for this requirement ;-) 

So if I understand you each VM need a seperate VLAN for communication with the switch. I mean a VM is bound to port group on the VDS and the port group in turn is build from a EPG. Each EPG has a dynamic VLAN mapped. So for my understanding each VM which is bound to one port group use together this VLAN?! 

allocation.  Again, remember, it is easy to add MORE VLANs to a pool, but very hard to remove them, so if your VMM Domain is planned to have 100 VMs, begin with a pool size of 100.

So your observation that

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The number of a dynamic VLAN for VMM domain seems always arbitrary. 

Regards

Udo 

[richmond · Accepted solution]

You need 1 VLAN in the pool for each vSphere Distributed Switch the EPG will be created on, plus another if you use Intra-EPG Isolation, Intra-EPG Contracts or Micro-Segmentation (these features use PVLAN in the switch and consume 2 VLAN tags). APIC does not re-use the same tag for the same Port Group configured on multiple vDS (not sure why.... but it doesn't).

Take the number of EPGs, multiply it by the number of vDS in your environment they will appear on, if you use any of the PVLAN features then double this number for the quantity that use them, then add some room to grow. The nice thing is you can easily add more to the pool, so you don't need to go too far with future growth.

[udo.konstantin]

Thanks, this is what I want to know!