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802.11 Frames: An In-Depth Overview

I cover a number of advanced topics on the 802.11 protocol and walk you through the different types of 802.11 frames and their purpose. I show how a packet turns into a frame; how that frame turns into bits; and, lastly, how the bits get modulated into the air.  

You have heard that Wi-Fi is half duplex, right? Let's tackle the complex discussion of CSMA-CA and break down Layer 1 Carrier Sense and Layer 2 Network Allocation Vector, explaining how both work in concert to make sure of a lower probability that two or more stations will not transmit at the same time. I also give a status of my All Wi-Fi office (AWO) with Cisco 3700 802.11ac access points.

You just deployed Cisco 802.11ac access points, and you want to sniff frames? No problem. I share my real-world experience sniffing 802.11ac frames with Wildpacket OmniPeek directly from Cisco 3700s.

If you design, deploy, or manage a Wi-Fi network, do not miss this session.

Agenda

•  Management, control, and data frames

•  LLC, MAC, PLCP, PMD: Know the layers and what each layer does

•  CSMA-CA (Layer 1) Carrier Sense and (Layer 2) Network Allocation Vector

•  How to capture 802.11ac frames from a Cisco access point

 

Cisco Designated VIP George Stefanick is a wireless architect employed by Houston Methodist Hospital System. George manages a large and complex wireless network that includes more than 2500 access points and upward of 11,000 concurrent Wi-Fi clients. George has been in wireless communications since 1997 and holds various vendor and vendor-neutral certifications. He focuses on high-density indoor deployments in the healthcare vertical, thereby using his hands-on experience in site survey, RFID, and voice design. As a consultant, George has consulted with Fortune 500 companies using his real-world hands-on experience to meet the needs and challenges in today’s enterprise environments. George is a Cisco Support Community VIP 2012, 2013, and 2014 and Aruba MVP 2014.

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Last update:
‎08-18-2014 12:25 PM
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Comments
New Member

Hi George,

 

Thanks for your talk, it was an interesting lecture full of valuable information. I'd like to expand on the authentication process in 802.11 that you described.

Citing:

"this is simply the jack plugging in to the wall, so to speak. Probably, not the right term to call it - authentication"

Obviously, we're not talking about the 802.11i sort of authentication, which was proposed much later than the original 802.11 standard, thus the simple 2-way authentication was the only one back in years. Can't the reason behind the "authentication" term be in the possibility of other (much simpler) authentication mechanisms being employed with 802.11 at this initial "plugging-to-the-wall" stage, like MAC filtering, for example? If the client's MAC address is blacklisted (or missing in the whitelist), the AP will usually respond with authentication denied response (before even starting the association phase). While the MAC address based authentication scheme is rather naïve, it can still be considered an authentication, and in fact it's still being commonly used in small deployments.

 

Another authentication (and encryption also, but that's not important right now) scheme can be set up with WEP, which you did not talked about much. I'm not sure about the details here (please correct me if I'm wrong - it's just my guess), but can't it be that WEP authentication actually runs exactly in this stage? Then it would make some sense.

Moreover, it could be theoretically possible to create a WiFi network that is protected both by WEP and WPA (for no particular reason, just as an excercise). The client would be asked to authenticate via WEP first (as L2 authentication), then it would be associated with the AP (so L2 would be operational), and finally it would undergo WPA(2) authentication process.

This is just theoretical brainstorming, but I believe it helps understanding the concepts and differencies between WEP and WPA(2) schemes, showing the different layers they operate on.

 

Any thoughts on this?

--

Jozef