Introduction to Wireless Networks

This topic is to discuss the following lesson:

Good job Rene

very much thanks to Rene

Very good job Rene

Hi Rene,

Checking in to see if there’s addition Cisco wireless course material I missed somewhere on your site?

Many Thanks!
Joey

Great Explanation - Thanks

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Hello Rene in this lession you have mentioned we can run wireless packet sniffer to detect SSID incase of SSID broadcasting is disable, bot how without connecting to any nework, it will not show anything, will wireshark work help to capture SSID wich is not broadcasting.

Hello Sanjib

When performing packet sniffing on a wireless network, there are several options. The first as you mentioned is to actually connect to the wireless network and simply use Wireshark as you would with a wired connection. Where wired connections take advantage of Winpcap libraries (for windows computers) wireshark uses what is known as Airpcap to support the capturing of wireless packets.

But you can also run wirehshark in what is known as monitor mode, which allows you to listen in to packets being transmitted by both clients and access points without actually needing to successfully connect to a network. This is one of the major security disadvantages of wireless networks, that everyone can “hear” everyone else if they are within range. Fear not however, with sufficient wireless security methods, this disadvantage is indeed mitigated. You may be able to capture all packets within range, but you won’t be able to “see” the contents of those messages if security measures have indeed been taken correctly.

In monitor mode you will be able to to capture management packets that contain the SSID even if the AP has been configured not to broadcast that information.

Keep in mind however that a lot of this is very platform/network adaptor/driver dependant, so you may get different results with different combinations of these.

In any case, you can view details of how to capture packets on wireless networks using Wireshark at this Wireshark Link.

I hope this has been helpful!

Laz

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Thanks for good explanation.
I have two questions.
First, why does 2.4 GHz band have only 14 channels?
Isn’t it possible to make the range of each channel smaller than 22 MHz and to create more than 14 channels?

Second, why are the data rate of 802.11a and 802.11g the same, even though they use different frequencies?
Can’t we transfer faster when we use higher frequency?

Hello Kazuaki

The reason for the number of channels is simply the definition of the standard itself, the available range of frequencies in the specific band, and the width of each individual channel. When it was conceived, 11, 13, or 14 channels (depending on where in the world you are) of which only 3 are non-overlapping, was considered enough for the needs of the day. For this reason, the specific frequencies were defined, and the specific width of each channel was defined.

Technically, it is possible yes, but in order to do so, you must change the standard. The standard however has been set, and all manufacturers comply with that standard. If you create smaller channels, both end devices and access points must support this. There are no plans to change this standard at the present time.

Even so, making the channel widths smaller will cause a decrease in available bandwidth, since from a physics standpoint, the smaller the width of the channel, the less bandwidth it can handle. However, the width of the channel is not the only thing that can affect the bandwidth, but it is just one of the fundamental parameters that defines it.

It is true that higher frequencies are capable of carrying higher data rates, but again, the frequency is not the only characteristic that affects bandwidth. The methodology used to place data on the carrier wave is also involved in this. Each standard is designed to provide specific capabilities at specific frequencies.

The main purpose of 802.11a was to provide a wireless service in a “less crowded” frequency range of 5GHz. It was the first to use Orthogonal Frequency Division Multiplexing (OFDM) which gave it the capabilities of up to 54 Mbps. Several years later, OFDM was used to define the 802.11g standard which yields the same speed. So you see in this case, the use of OFDM was the defining factor as far as the available speeds go.

Physically speaking, higher frequencies can carry higher data rates, but this is only true if the methodologies with which data is placed on the carrier waves takes advantage of this physical capability.

I hope this has been helpful!

Laz

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Thank you Laz for your kind explanation! It’s very helpful!

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Hi Rene

CCNP Enterprise 350-401 ENCOR has Antenna topics like Patch / Yogi antenna’s etc.

But i don’t see that in your 350-401 course here.

Thanks
Venu

Dear Sir,

 AP model is AIR-LAP1142N-S-K9   
 WLC model 5508

How to make signal adjustment based on the SSID in Access Point to reduce the signal leakage ?
Is there are some settings that can put in to prevent clients with weak signal strength from connecting to AP?
Will appreciate your help.

Thank you

Regards,
Mani

Hello Manikandan

Signal strength can only be set per access point (more specifically per radio) and not per SSID. Because the same radio transmits multiple SSIDs, it’s not possible for that radio to send different SSIDs at different power levels. There are several best practices that you can do to ensure that clients at the edge of your access point’s range don’t connect with a weak connection.

  1. Rarely set your signal strength to maximum, but keep it “somewhere in the middle”. I know that’s a bit vague, but the point is this: If the signal strength is too high, then clients at the edge of your coverage may get the signal but will have trouble sending it back. The following Cisco community thread describes this well:
    https://community.cisco.com/t5/wireless-security-and-network/increase-signal-strength-of-a-single-air-cap3602i-a-k9-access/td-p/3675709
  1. The signal strength shown by clients does not only have to do with signal strength!! SSIDs that advertise lower data rates will also show a lower signal strength on the client. Again, the following link describes this more: https://community.cisco.com/t5/other-wireless-mobility-subjects/different-signal-strength-on-ssids/td-p/1142645

I hope this has been helpful!

Laz

Please post lecture on WLAN RF Fundamentals. You are doing good job and i have gone through Routing and gained a lot.

Hello Sachin

We’re glad that you have found the lessons and their content useful! Also thanks for the suggested topic. You can go to the Member Ideas page and post your suggestion there. You may find that other users have also suggested something similar, so you’ll be able to add your voice to the topics already found there too.

I hope this has been helpful!

Laz