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Frequent Contributor I

vlan pooling - hash vs round robin

Wondering if anyone is using the new round robin feature for user vlan distribution, and can comment on benefits and drawbacks versus the static hashing algorithm method.

We are upgrading our M3s soon and could definitely use this feature if there are not too many negatives.

Thanks!

 

Marcelo

Marcelo Lew
Wireless Network Architect-Engineer
University of Denver
Guru Elite

Re: vlan pooling - hash vs round robin

If you feel your ip addresses are not being allocated across a pool using the default hash method, try the even vlan method to see if it makes it more fair.  There are certain environments where it will never really be even.  It also depends on the fact that a VLAN is only assigned to one controller, because controllers do not share VLAN utilization information.  It also depends on the fact that all of your leases are the same among VLANs.

 

Again, there is a strong possiblilty that your VLANs will NEVER have even distribution due to clients being assigned to vlans, but leaving at will...

 

From the user guide:

 

"

The VLAN assignment type determines how a VLAN assignment is handled by the controller.

The Hash assignment type means that the VLAN assignment is based on the station MAC address. The Even assignment type is based on an even distribution of VLAN pool assignments.

The Even VLAN Pool assignment type maintains a dynamic latest usage level of each VLAN ID in the pool. Therefore, as users age out, the number of available addresses increases. This leads to a more even distribution of addresses.

The Even type is only supported in tunnel and dtunnel modes. It is not supported in split or bridge modes and it is not allowed for VLAN pools that are configured directly under a virtual AP. It can only be used under named VLANs.

If a VLAN pool is given an Even assignment and is assigned to user roles, user rules, VSA or a server derivation rules, then while applying VLAN derivation for the client “on run time,” the Even assignment is ignored and the Hash assignment is applied with a message displaying this change. "

 

 



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

Frequent Contributor I

Re: vlan pooling - hash vs round robin

Thanks CJoseph.

 

"It also depends on the fact that a VLAN is only assigned to one controller, because controllers do not share VLAN utilization information."

 

This is something I definitely need to consider.  I could break up the pool I have now (about 30 vlans), and assign one pool to each controller and enable l2 roaming.  Might defeat the purpose of even vlan distribution thou :smileyfrustrated:

 

is not allowed for VLAN pools that are configured directly under a virtual AP. It can only be used under named VLANs.

 

Do I have have to name each vlan and do the even command per vlan, OR, can I create a named vlan pool (assigned my vlans with no name), and tell AOS to do even distribution for that entire named vlan pool?

 

Thanks,

 

Marcelo

Marcelo Lew
Wireless Network Architect-Engineer
University of Denver
Guru Elite

Re: vlan pooling - hash vs round robin


mlew2433 wrote:

Thanks CJoseph.

 

"It also depends on the fact that a VLAN is only assigned to one controller, because controllers do not share VLAN utilization information."

 

This is something I definitely need to consider.  I could break up the pool I have now (about 30 vlans), and assign one pool to each controller and enable l2 roaming.  Might defeat the purpose of even vlan distribution thou :smileyfrustrated:

 

is not allowed for VLAN pools that are configured directly under a virtual AP. It can only be used under named VLANs.

 

Do I have have to name each vlan and do the even command per vlan, OR, can I create a named vlan pool (assigned my vlans with no name), and tell AOS to do even distribution for that entire named vlan pool?

 

Thanks,

 

Marcelo


You can only do even VLAN pooling from a named VLAN or a Named Pool of VLANs...  That is where you would configure the "even" setting.



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

Regular Contributor I

Re: vlan pooling - hash vs round robin

Hi forum,

 

Does the hash method for vlan pooling work in a binary fashion? and if so is it better practice to use a "X to the power 2" number of vlans with in the pool? ie.. 2,4,8,16 etc.

 

The use case I have is increasing capacity on pools directly configured on the VAP. 

 

I dont rather not add a couple more vlans (to a total of 6) to find that the first 4 have 50% assignments and the last 2 have 50% assignments. 

 

Does that make sense?

 

Cheers guys!

 

Nik

Guru Elite

Re: vlan pooling - hash vs round robin

Nik,

 

Regardless of how many ip VLANs you dedicate, there will always be a certain number of unused ip addresses, so that you do not run out.  VLAN pooling's main benefit is to keep you from having to completely restructure a subnet, by just adding a VLAN you can expand capacity.

 

With that being said, the "waste" is specific to your environment.  Not only does it depend on space, it also depends on the length on your DHCP scopes.  You need to experiment to determine the happy medium in your own environment.  You could ideally use a single subnet sized to your needs and be done with it.

 

EDIT:  Please see if the post here:  https://arubanetworkskb.secure.force.com/pkb/articles/FAQ/What-is-even-vlan-pooling-and-how-is-it-better-than-the-previous-Hash-based-VLAN-pooling-mechanism answers your question...

 



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

New Contributor

Re: vlan pooling - hash vs round robin

Hi, quick additional question tio this old post.

 

Chuck just mentioned just now on a UHD VRD that the recommendation is to use a single big VLAN (which is pretty standard for large arenas etc) rather than VLAN pools.

 

I questioned him whether using the "preserve-client'vlan" feature would assist with VLAN pools with regards roaming events and IP mobility / re-use.

 

Chuck answered it depends on the pooling method used, but didnt have time to go into any more detail.

 

My assumption was that the "preserve-client-vlan" would help more for the even distribution method than for the hash method - please could you advise on this?

 

Many thanks, Ash.

Re: vlan pooling - hash vs round robin

http://community.arubanetworks.com/t5/Controller-Based-WLANs/What-is-Preserve-VLAN-knob-do-on-Virtual-ap-profile-and-It-s-use/ta-p/234131

Thank you

Victor Fabian
Lead Mobility Engineer @ Integration Partners
AMFX | ACMX | ACDX | ACCX | CWAP | CWDP | CWNA
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