NAV and foreign STAs

The Sybex CWAP 2011 study guide contains a gem regarding how different BSSs interact:

[with the exception of transmitter and receiver,] Any other client or AP stations within hearing range on the same channel will reset their NAV, even if they are nont members of the BSS.

Chapter 3 review questions, q.10, answer p.120

It is the first time I find it clearly stated that STAs contending through HCF or EDCA will abide to any information they can decode from received frames, regardless if they are from the same BSS or not.

This makes sense, because:

  • APs know the AID of the members of it’s BSS, but client STA don’t;
  • any STA (AP or client) does physical carrier sense SD when it decodes a preamble, and it is likely to also decode the header which contains a length field which is the time it will take to transmit the frame (in microsecs);
  • Therefore it’s logical to use a NAV if it can decode it.

Perhaps this should be put in the CWNA study guide explicitly.


Passed CWSP certification!

Today I took the CWSP exam and passed it with 90%. It’s exactly one year after I passed CWNA and the satisfaction and sense of accomplishment is great. The original plan was to study during winter and spring 2020 in order to take the exam in April. Then the COVID19 pandemic hit and changed all our priorities.

The current exam was CWSP-206, which has an official study guide from Certitrek (authored by Badman, Bartz, Carpenter, Hill, Morgan) and an almost updated (CWSP-205) study guide from Sybex (authored by Coleman, Westcott, Harkins).

A great guide by David Coleman, David Westcott and Bryan Harkins

It’s good to study both books: the Sybex is a high quality reference guide to understand our work, and the Certitrek a more exam-oriented tool with great content, but somewhat poor editorial depth (e.g. no chapter/section navigation, no index).

How to pass an exam and have fun with Kali Linux

I did not practice or setup a lab specifically for this exam, as most of my day to day work already touched most of the topics. Keeping up to date with blogs, Twitter and webinars was very useful, see my Twitter profile @MonorailHandles for my followed profiles which are almost all wi-fi related.

The CWNP practice tests were very useful to gauge my level of readiness and study the finishing touch. As with CWNA, the pass threshold is 70% and having scored 90% in the exam means I overstudied and delayed: chalk it up to an astonishing year with a pandemic, african locusts swooped over Milano by high altitude winds, and an earthquake near home.

Pearson Vue’s online proctored exam worked smoothly, I sat in an empty room at my office and the absolutely bare space may have helped the experience. It’s a good alternative to the physical exam center, in both convenience and comfort.

Now to the next thing: the original plan was CWDP, but my interests and professional curiosity drive me towards CWAP. Let’s see in the next weeks.


CWNA study guide review

David D. Coleman, David A. Westcott
CWNA Study Guide Fifth edition, Exam CWNA-107
Sybex, 2018

This book has been my companion since I started working in my employer’s entrerprise wireless LAN in late 2018. It’s a foundation guide that gave me the right approach to wifi networking and architecture. It’s also a technical reference guide for the many situations facing a WLAN administrator during the day to day operations of designing, deploying, validating and troubleshooting an enterprise WLAN.


About ghost frames

A recent WiFi Ninjas podcast (part 1 and part 2) is a long interview with Ben Miller about channel utilization, spectrum analysis and data rates. Miller talks also about so-called ghost frames, a concept I don’t understand very well.

A ghost is a preternatural being that haunts the living – ghost frames is a negative term, a statement of trouble, a problem. I tried to make sense of this statement reading Devin Akin’s article on ghost frames, and reopening my CWNA study guide (chapter 8, 802.11 medium access).

This notes are my tentative thoughts on the issue, there are probably mistakes, but writing it in English I feel I can think more clearly. I hope that the people quoted will not take offense for my representation of their ideas.


CWSP guide received

just delivered!

I’m a CWNA now!

I passed the Certified Wireless Network Administrator certification exam on Dec 19th, 2019!

My CWNA certificate
The certificate is generated about 24 hours after passing the test

It’s been a long journey starting 18 months ago, when I moved from network security to wireless networking and I realized that everything in wifi is totally upside-down from the wired world.

I dived into my new job, and on the sideline studied everything I could lay my hands on, starting with the CWNA Study Guide by Coleman and Westcott and published by Sybex. This book goes beyond the task of exam preparation and is a reference work to keep always on the desk.

Sybex CWNA Study Guide by Coleman and Westcott
A handy 900+ pages tome of wifi wisdom

The study guide has a list of blogs, conferences and Twitter handles that is a good starting point for following the wifi universe. I recommend the WLPC videos from the WLAN professional community, great for technical drill-down and (to non-native english speakers) for a taste of english technical terms.

CWNA-107 is the current certification exam version. It was updated from CWNA-106 around 2017 and it may be overhauled in 2020. You can check the official CWNP site for exam details, costs and study materials.

There was also a copy of the CWNA-107 Official Study Guide published by CertiTrek laying around in the office, but did not read it. My colleague (and now fellow CWNA) Claudio Lori liked that it’s condensed, more exam-focused.

While preparing the exam I kept working on my employer’s infrastructure: It’s a privilege I could apply new knowledge to real-world problems and make practical sense of otherwise abstract issues.

I was almost ready for taking the exam when my employer booked me and my colleague to a CWNA training class by Devin Akin (CWNE #1) in Milano. It was a fantastic, challenging week that defined me professionally, an eye-opener experience that motivated me to pursue the CWNP path.

After organizing my study notes and going over the Exam Objectives document for the last time, I purchased the Practice Test and the Exam Voucher on the CWNP site, then eventually booked a test date in Milano.

The practice test is completely optional. It has 2 banks of 60 questions that closely match the quality of the official test. After completing the 2 banks with a high score I was fairly confident that I could pass the real exam.

Still, when the exam date came and I was sitting at the testing center, I was a little nervous before clicking the last and final submit button, and immensely relieved when I was instantly presented with the exam results and the pass score. Yeah!

Now there are lots of plans for the future: more on that in the next posts.