Wireless broadcast domain size

Unanswered Question
Aug 29th, 2010

What is the largest suggested broadcast domain that can be used in a wireless lan using 6509's with wism controllers? We are a university and we have issues with students pulling ip's with their mobile devices because their wireless is turned on thus depleting our ip space.

I have this problem too.
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Leo Laohoo Sun, 08/29/2010 - 19:04

Bring down the lease time.  I'm not familiar with the size of your student population but I guess you reserve, say, /20 but you configure /23.

Randy Ethridge Sun, 08/29/2010 - 19:18

We have around 11,000 students. We have one /22 wireless lan that a two hour lease time causes depletion a few times a day, one hour causes depletion maybe once a day and 30 minute keeps up. We also have a NAC appliance that doesnt want any shorter than 4 hour lease to limit the number of times it has to write ACL's in the route map, but thats another story.

Leo Laohoo Sun, 08/29/2010 - 19:32

We have around 11,000 students. We have one /22 wireless lan that a two hour lease time causes depletion a few times a day, one hour causes depletion maybe once a day and 30 minute keeps up. We also have a NAC appliance that doesnt want any shorter than 4 hour lease to limit the number of times it has to write ACL's in the route map, but thats another story.

CRICKEY!   11K student body?

How about setting aside a /20 subnet but configure a /21 and see if that works?

You don't have dorm rooms part of your wireless campus, would you?

Randy Ethridge Sun, 08/29/2010 - 19:39

We are just starting to add dorm rooms, partly why Im asking this question. They will have all those mobile device on all the time so they will be taking several ip's each. My plan is to take part of the switched network ip space and move it to the wireless since the switched network usage will be reduced as we light up more wireless.

Leo Laohoo Sun, 08/29/2010 - 19:49

We are just starting to add dorm rooms

Basically that means that your DHCP server will be dishing out IP addresses 24-hours a day.  Too bad, I thought that with WCS you can disable the radios for, say, an hour and that might help refresh the list.

In that case, I'm sure /20 is enough.  I recommend that you subdivide the network to a "per building" basis.  That way you can better manage the way IP addresses are being used.

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