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© 2008 Cisco Systems, Inc. All rights reserved. IUWNE v1.0—1-1

Wireless Fundamentals

Reviewing the Wireless Frame Journey: End-to-End


Discovering the Network


Getting Connected


Clients in Cells


Sending in the Cell


Creating the 802.11 Frame


Acknowledging the Frame


AP Forwarding to Network


AP Forwarding to Controller


In the Controller, Header Is Rewritten


Wired Segment


In the Controller, on the Way Back


The AP Forwards the Answer


Using the Optimal Speed


The Right Client Processes the Frame


All Frames Are Sent to the Same AP Radio


Controller Needs to Keep SSIDs Separated


VLANs

VLAN = Broadcast Domain = Logical Network (Subnet)


VLAN Operation


802.1Q Trunking


Understanding Native VLANs


Mapping SSIDs to VLANs

Each SSID is mapped to a VLAN:1 SSID => 1 subnet and 1 VLAN tag


Configuring VLANs and Trunks

1. Create or modify a VLAN on the switch.2. Assign switch ports to a VLAN and verify.3. Save the VLAN configuration.4. Configure and verify 802.1Q trunks, and save.


The maximum number of VLANs is switch-dependent. VLAN 1 is the factory default Ethernet VLAN. Cisco Discovery Protocol is sent on native untagged VLAN. The Cisco Catalyst switch IP address is in the management

VLAN (VLAN 1 by default).

VLAN Creation Guidelines


Adding a VLAN


Assigning Switch Ports to a VLAN


Verifying VLAN Membership


Verifying VLAN Membership (Cont.)


802.1Q Trunking

Make sure that the native VLAN for an 802.1Q trunk is the same on both ends of the trunk link.Note that native VLAN frames are untagged.


Configuring 802.1Q Trunking


Verifying a Trunk


Summary

When wireless frames transit to the wired side of the network, the body is unchanged but the header is transformed to a 802.3 header.

VLANs provide on Ethernet segments the segmentation that SSIDs bring to the wireless side.

VLANs create tags on frames, and trunks carry these framed tags from switch to switch.

VLAN membership can be static or dynamic. Controllers tag frames, and the other end, which is a switch, has

to be in trunk mode. A switch has a “native VLAN,” which is usually not tagged on a

trunk. Configuring static VLANs consists of creating them and assigning

a port to them.


Technology

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