ArubaOS and Controllers

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Regular Contributor I
Posts: 236
Registered: ‎04-03-2007

mixing subnet sizes in a vlan pool

I understand now that a maximum of 32 VLANs can be configured in one VLAN pool.

Is it ok to mix /23's and /24's in that one pool? Will the controller still be able to accurately identify the least-used VLAN, based on current user counts of each VLAN in the VLAN pool, or will that break the algorithm?

Thanks!
Mike
Aruba Employee
Posts: 664
Registered: ‎04-15-2009

Re: mixing subnet sizes in a vlan pool

Michael,

You should not mix subnet sizes. The controller hashes the MAC address to determine the VLAN in which to place the client. There is no feedback mechanism to make sure the DHCP server passed the client an address, so you would have a situation where a client was placed into a VLAN, but didn't get an address because it was in a /24 VLAN with no available addresses. This client would ALWAYS be placed in the same VLAN due to the hash algorithm.

Do you really have more than 8,000 users coming to a single controller? 250 addresses per VLAN X 32 VLANs in a pool = 8,000 users. If this is a multiple controller environment, can you break the VLAN pools up by controller? You can still use the same SSID profile.

If this is a single M3 controller, the limit is 8,192 users.
Regular Contributor I
Posts: 236
Registered: ‎04-03-2007

Re: mixing subnet sizes in a vlan pool

Thanks for clarifying my "subnet size mixing" question.

We have 6 local controllers hosting ~2,000 APs. All M3ks. I'm not sure what you mean by "break the VLAN pools up by controller". How would that reduce my number of vlans? We only have about 1,500 users on any given controller.

All vlans in the vlan pool are currently trunked to each controller. All APs are configured the same except some AP terminate on lms1, some to lms2, etc. They all have all the same vlans in the pool.

Thanks!
Mike
Aruba Employee
Posts: 664
Registered: ‎04-15-2009

Re: mixing subnet sizes in a vlan pool

Mike,

You could create an AP group and VAP for each controller and assign a unique set of VLANs to each VAP. That way, you could have 32 VLANs per controller. As I said earlier, you can still use the same SSID profile. This will actually increase the number of VLANs you have in use, not decrease them.

The one issue you MIGHT run into is roaming between controllers. A client would not be able to maintain a voice call or other real time data flow unless you enabled layer-3 roaming.

If you don't have a requirement to support real time traffic across your controllers, you could do this without layer-3 roaming.

You will also have to keep redundancy in mind. If you have a secondary LMS configured in your AP System Profile, you will have to make sure the primary and secondary both have the same AP groups configured.
Regular Contributor I
Posts: 236
Registered: ‎04-03-2007

Re: mixing subnet sizes in a vlan pool

For better or for worse one of our "large" SSIDs uses captive portal. Currently when a user roams across a controller boundary they keep their IP address but must re-log back in on the web page. Would your suggestion of separate VAP per controller using unique vlan pools help or hinder CP clients?

Mike
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