WLAN broadcasts

[jehuffman]

I am looking at implementing a WLAN across a campus on a 4-class C VLAN with an initial load of approximately 500 users to a maximum of 800 using AP 1200s. Does anyone know of the broadcast traffic that occurs? The only broadcasts that I can think of would be ARPs for the router since the clients would not be talking to each other. What kind of broadcast traffic comes from the 1200s? Has anyone implemented a WLAN with this many clients on a single VLAN before?

[derwin]

For that size I really recommend that you break up your broadcast domain.

WLAN is a shared media and half duplex so you will see very poor performance if you make it too large without breaking up the braodcast domains

A good rule of thumb when scaling WLAN is to ask yourself the question would you build the same network using only 10M half duplex hubs ( not switches) ?? If the answer is no there is a good chance that you will run into congestion and broadcast problems with WLAN

Why do you say the client will not be talking to each other ? It would be very unusual network to have 100% of the LAN traffic going off that LAN

[jehuffman]

Thanks for the quick response. I forgot to mention that the WAPs will be uplinked to switch ports, which should limit the subnet broadcasts. The only allowed devices connected to the WLAN are end user workstations (no servers or server applications) so we are anticipating that almost all traffic will be off the VLAN. Some incidental intra-VLAN traffic may occur as an end client maps a drive to another end client, but we expect this will be very limited.

In this network, end stations and servers reside on different VLANs and almost all traffic will be used to accessing e-mail servers and application servers on different VLANs.

Is there a solid solution for allowing end stations to seemlessly go from VLAN to VLAN without a noticeable loss of connectivity?

[derwin]

you will still havle all the AP's in the same broadcast domain that will take up radio transmitter time that maynot be needed with a different design

As to intra VLAN comms depends on your requirements

The AP's support VLANs so you could have different deparmentsts each in a vlan and all the switch ports to the AP's trunking than allow a router to look after inter vlan comms This will remove the need to roam between vlans

If you want to roam between vlans then you need to use IP mobility (mobile IP)

The AP's support proxy mobile IP which will remove the need to have a mobile IP stack on the client but will allow mobile IP operation

Here is the link on VLANs for the AP

http://www.cisco.com/univercd/cc/td/doc/product/wireless/airo_350/accsspts/ap350scg/ap350ch4.htm

And proxy mobile IP

http://www.cisco.com/univercd/cc/td/doc/product/wireless/airo_350/accsspts/ap350scg/ap350ch6.htm