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VLAN concept with WLC

Hi guys,

This is my VLAN background:

VLANs are used  to segment the network and break up the broadcast  domains in order to  reduce congestion and isolate network problems as  well as providing  scalability, performance improvement, security and  making network  additions, moves, and changes easier and more manageable.

And this is my wireless VLAN background with the controllers:

Host  A is a wireless LAN client communicating with the wired device, Host  B.  At the access point, the access point adds an LWAPP Header to the    frame and send it to the controller. After processing the 802.11 MAC    Header by WLC, it  extracts the payload (the IP packet), encapsulates  it   into an Ethernet  frame, and then forwards the frame onto the    appropriate wired network,  typically adding an 802.1Q VLAN tag.

According to Cisco's "Fundamentals of Wireless Controllers" video (starting at 2:53), the 5508 controller allows you to use much larger subnets and less wireless VLANs. So with a 5508 controller in a completely wireless  infrastructure (no wired hosts),

1. I don't need to break up broadcast  domains and have multiple subnets and I'm free to use a giant flat network?

2. If I'm allowed to use large subnets, as far as the broadcast traffics (other than ARP and DHCP which are specially handled by WLC) are concerned, how does the controller handle that? I think I still will need multiple VLANs to control them according to my following WLC broadcast handeling background:

"All traffic including broadcast sent to any destination by wireless  client get forwarded to WLC from its connected AP. WLC places the  broadcast message on to that VLAN, both wired and wireless clients that  are part of that vlan interface will get this broadcast message. Now,  the receiving wireless clients on that vlan can be associateded on to  any/different APs, APs mapped to different AP groups, even APs using  different L3 addresses from one or multiple WLCs, WLC inteligently  identifies the mapped VLAN interfaces and its respective APs through AP  group and forwards the broadcast(encapsulates) as Multicast packet to  those specific AP groups. Once APs receives the Multicast(broadcast), it  places it on the respective Radio's BSSID(where WLAN/ssid mapped) of AP  to reach the right wireless client. AP Radio's BSSID to SSID/WLAN to  interface mapping is pushed to AP by WLC at AP join. Also, Wired PCs  will receive the broadcast on its vlan as tagged(if tagged, otherwise  untagged) from WLC's interface, so does the other WLCs that spans this  vlan interface."

Regards,

Saman

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1 REPLY
Hall of Fame Super Silver

Re: VLAN concept with WLC

You should still follow your best practice for your subnet size. Remember that wireless is half duplex and only one device can talk at a given time. Also... The AP can be in a different vlan, ap group, etc, but the clients are still on the same vlan. So it means that the clients need to be on the same vlan, but the AP's can be on a different subnet since this doesn't matter.

Sent from Cisco Technical Support iPhone App

-Scott
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