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Posts Tagged ‘CCNA: Wireless

Why link latency is important for Cisco lightweight access points.

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Link latency, it’s a convenient little check box you turn on individually (or globally) on lightweight access points (Operating in FlexConnect/H-REAP or OfficeExtend) to see the latency details to the controller, while this is one of those ‘yea that’s nice to know’ type things it can be a key resource when troubleshooting certain WLAN issues.

First lets start with why knowing the latency is important, well Cisco has published the requirements for CAPWAP latency from the LAP to the controller and that requirement is no more than 300 ms of latency. Now while most enterprise’s do not have to worry about those latency requirements too much (due to a typical MPLS, VPLS, or metro backbones) other types of companies that lets’s say rely on a pretty common DMVPN over the Wild West (the Internet) may have to keep in mind these latency requirements. If you do not meet these latency requirements you might be seeing CAPWAP packets drop in transit or your Flexconnect/H-REAP LAPs flapping between ‘Connected’ mode and ‘Standalone’ mode which depending on your setup can cause a host of issues.

Link latency will monitor the following:

  1. The round trip time of the CAPWAP heartbeat, it does this by comparing the timestamps of when the request is sent to when the reply is received. Now, by default this CAPWAP heartbeat occurs every 30 seconds and this CAPWAP latency is different from normal network latency, as the CAPWAP heartbeat also has a dependency concerning how quickly the controller can process the request and send the reply back out.

Something to keep in mind about the link latency stats, is the fact they do not reset unless the LAP reboots or they are manually cleared so if you decide to turn on link latency come back 6 months later and review the states you are not going to get any useful information.

Configuring and viewing Link Latency

Configuring and viewing Link Latency

As you can see from the above screen shot link latency will provide you a quick glance of the current latency, minimum latency, and the maximum latency to the controller. (From when link latency was first enabled or last cleared)

Written by Stephen J. Occhiogrosso

June 21, 2013 at 5:20 PM

My thoughts on the CWTS exam from CWNP.

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Last week I went ahead and took the CWTS (Certified Wireless Technical Specialist) exam from the CWNP group, now I know they consider this almost a “sales” certification but I wanted to start with this exam just to see how the CWNP group present their exams compared to Cisco, Microsoft, RIM, and CompTIA. Well I managed to pass the exam with a 90% (70% is the minimum score required to pass) so I did fairly well on the exam. I did think a few of the questions were not worded in the best way, but it appears I understood what they were asking for.

My primary sources of study was the Official CWTS study guide from CWNP, along with their practice exams hosted off the CWNP website, not to mention a few years of supporting multiple wireless networks. Now I’m not usually one to say “yea get the official study guide you’ll be ok with that” but in this situation I have to recommend the official study guide. It does an amazing job at covering the CWTS exam objectives. Plus I found it a very easy book to read there plenty of clear concise explanations with enough images that promote the text (Images also span between some of major WLAN equipment vendors Cisco, Proxim, Motorola, etc). The only downside I found concerns the material on the CD that is included with the book.  While it does come with sample tests and flash cards I found a few of the questions to be incorrect, another reason to purchase the online practice tests.

Now the material on this exam are the fundamental basics of a WLAN (pertaining to the 802.11 standards, the RF spectrum, and WLAN hardware) and because of that I really do recommend this to any type IT professional who is new to working with WLANs. Whether you are help desk/field technician or even a network administrator that needs to support/implement a new WLAN this book does deserve at least one look over. When I first started working with WLANs I would have loved to have this book it would have saved me hours of research back then. However if you are like me and you have plenty of experience with wireless already I would skip the CWTS and go straight for the CWNA certification.

Now that’s a rap for the CWTS, considering my experience with this exam and the material, I will be pursuing my CWNA certification later on this year but I want to squeeze in a lot of study time for the CCDA exam before Cisco retires the 640-863 April 30th. It’s a certification I tried pursuing a long time ago but just never dedicated that much time to, however between then and now I’ve read many Cisco design guides and both 640-863 Cisco Press books. So if you notice my upcoming entries leaning more towards network design consideration that’s why.

Written by Stephen J. Occhiogrosso

February 20, 2011 at 3:09 PM

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