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Frequent Contributor I
Posts: 97
Registered: ‎08-19-2008

Vlan Pooling Algorithm?

Will a machine go thru the vlan pooling algorithm every time it tries to get on the network? We see a bit of a disparity between subnets on a vlan pool, up to 60+ users more on one than the other for example. We are pretty slow during the summer here, and when school year starts (today) we see a huge increase in usage (and the disparity starts). Should we be “flushing” somehow this vlan pool algorithm?
Thanks,
Marcelo Lew
Wireless Network Architect-Engineer
University of Denver
Guru Elite
Posts: 20,008
Registered: ‎03-29-2007

Hash...

The VLAN pooling algorithm is a hash that distributes clients based on their mac address. Clients will always get placed into the same VLAN. Think of it as this:

If you have 3 VLANs in a pool, the user's mac address is divided by three and whatever the remainder is, that is the VLAN the user gets placed in. There are reasons why this will not be even based on your number of clients and how many come and go during the day. There is no re-balancing of clients.
Colin Joseph
Aruba Customer Engineering

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Validated Reference Design Guides : http://community.arubanetworks.com/t5/Validated-Reference-Design/tkb-p/Aruba-VRDs
Frequent Contributor I
Posts: 97
Registered: ‎08-19-2008

Re: Vlan Pooling Algorithm?

Thank you for the info.
Marcelo Lew
Wireless Network Architect-Engineer
University of Denver
CmC
Occasional Contributor II
Posts: 11
Registered: ‎08-15-2010

Available addresses in pool

I have a pool of 5 /24's and the first is getting filled up... with only 14 addresses left. Can I assume if there is no re-balancing then there is a good possibility that one scope could get filled to capacity and cause clients problems (that were previously in that scope). I average 450 wireless (captive portal) users and sometimes peak up to 680. Should I double the available host addresses in each subnet? I'm using Microsoft DHCP.
Thanks in advance.
Guru Elite
Posts: 20,008
Registered: ‎03-29-2007

No Rebalancing

There is no rebalancing. The best thing you can do is to ensure that the least times are short on your DHCP scopes and that they match, as well.
Colin Joseph
Aruba Customer Engineering

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

Validated Reference Design Guides : http://community.arubanetworks.com/t5/Validated-Reference-Design/tkb-p/Aruba-VRDs
CmC
Occasional Contributor II
Posts: 11
Registered: ‎08-15-2010

Re: Vlan Pooling Algorithm?

Ok Thanks. Let's see if 8 hrs is enough.
CC

Edit: 8hrs seemed to do the trick for me. Captive Portal timeout is 2 hrs for me fyi.
Frequent Contributor I
Posts: 97
Registered: ‎08-19-2008

Re: Vlan Pooling Algorithm?

What Aruba code will have vlan pooling "round robin" placement instead of the algorithm? 6.0?
Just double-checking about this algorithm in 5.0 code: Will the same client (mac-address) ALWAYS get placed on the same vlan if no vlan has been added or deleted from the vlan pool?
And, if you add a subnet to the pool, then I understand the client will get place on a different subnet, BUT, if I remove this subnet I just added, will the same client get put back on the original subnet? In other words, is this a static predictable algorithm?

Thanks!
Marcelo Lew
Wireless Network Architect-Engineer
University of Denver
Guru Elite
Posts: 20,008
Registered: ‎03-29-2007

Re: Vlan Pooling Algorithm?


What Aruba code will have vlan pooling "round robin" placement instead of the algorithm? 6.0?
Just double-checking about this algorithm in 5.0 code: Will the same client (mac-address) ALWAYS get placed on the same vlan if no vlan has been added or deleted from the vlan pool?
And, if you add a subnet to the pool, then I understand the client will get place on a different subnet, BUT, if I remove this subnet I just added, will the same client get put back on the original subnet? In other words, is this a static predictable algorithm?

Thanks!




Not sure if and when "round robin" will enter production. Today the same client mac address will ALWAYS get placed in the same VLAN, correct. If you add a VLAN the client *might* get placed on a different VLAN. If you remove a subnet, that also changes the algorith and the client *might* get placed on the original subnet. It changes every time you add or remove a VLAN.
Colin Joseph
Aruba Customer Engineering

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

Validated Reference Design Guides : http://community.arubanetworks.com/t5/Validated-Reference-Design/tkb-p/Aruba-VRDs
Occasional Contributor I
Posts: 5
Registered: ‎12-01-2010

Re: Vlan Pooling Algorithm?


I have a pool of 5 /24's and the first is getting filled up... with only 14 addresses left. Can I assume if there is no re-balancing then there is a good possibility that one scope could get filled to capacity and cause clients problems (that were previously in that scope). I average 450 wireless (captive portal) users and sometimes peak up to 680. Should I double the available host addresses in each subnet? I'm using Microsoft DHCP.
Thanks in advance.




I have that problem too. If your network is so big, I think you have no choice
but change to use less vlan pool and have a bigger address pool say /23 for
each pool. Although this is in the opposite way of vlan pooling to min broadcast
in a subnet, I don't think you can have a better choice unless Aruba change
the code to set a max client per pool. I had made such request but seems no use.
Aruba Employee
Posts: 571
Registered: ‎04-17-2009

Vlan Pooling Algorithm?

You should not go to /23. That's a bad idea. You really want to keep the broadcast domains as small as possible. Why not add a couple more VLANS to your pool?

Also, if you have an open SSID, you are probably losing addresses to people passing by. I would recommend shortening your lease times on the DHCP server. Bring that down in increments. You don't want to cause unnecessary ARP traffic if you don't have to.

Zach
Thanks,

Zach Jennings
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