Is there a DHCP Black Hole in Cisco WLC 7.0.116.0 new feature Vlan select?

[edwardzeng]

Hi,

Is there any potential DHCP black hole in the VLAN Select for WLC 7.0.116.0?

Like if you put 3 different subnets into one group interface, if one of their dhcp ip pool is full. As WLC is running round-robin load-balanced.

How does the WLC know that special vlan DHCP pool is full and avoid it?

(Becuase we could not make sure each subnet IP pools have the same utilization, some user may log out soon others may stay online for long time. )

Many thanks

Edward

[craig.eyre]

Edward,

I'm looking into the same issue/problem as you.

If you look at your wlc for the cli and type "show interface group detail "group name" it will show you the interfaces that are marked as "dirty" for dhcp requests. If you've never heard or read about this, here is a link to a doc explaining it.

I know it pertains to other features as well but the first section is on vlan select and its steps

http://www.cisco.com/en/US/products/ps10315/products_tech_note09186a0080b78900.shtml

He did notice initially that out of our 12 interfaces at least 10 would go "dirty" and in turn chew up all the ip's in a given pool. We changed out lease times to 1 hour from 1 day and it seems to be making the process smoother. If you have clients that auth and de-auth quite frequently then you might start chewing up ip's if your lease times are high.

I'm no expert but just looking into the same problem right now.

Regards,

Craig

[edwardzeng]

Hi Craig,

Thank you kindly for your suggestion. It is very helpful.

This link is very usefull too.

Currently we are using the big flat subnets for our SSID and plus the AP groups for different areas. (Our DHCP least time is 2 hours.).

Next stage we may allow the P2P client traffic for some applications, which means out big flat subnet may have heavy RF duty cycle due to the domain broadcast.

We are considering to move the big flat subnets back to multi-small C classes subnets.

But I am worring about the multi dhcp pools utilization.

Many thanks again,

Edward