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Revision Notes:Cisco Wiressless Fundamentals

Below are some revision notes I have made, Cisco have recently changed the certification requirements for wireless examination, I am yet undecided if these notes shall be finished. Some of this material is old, it’s usefulness may vary !

I thought it’d be cool to share some of my revision notes :cool:

Chap 1: Introduction.
Wireless started out in the mid eighties (1986) for warehouses & retail business to ease stock control. It was from this technology that Enterprise and HomeUsers saw that they could be freed from the wires on their desks. Wireless data networks span a large area of technologies from infrared to satellite, fortunately cisco’s Fundamentals course only covers LANS (Local Area Networks), Cisco is also part of the body which standardises wireless communications - Wireless Fidelity (WI-FI), This is apparently important to remember because they provide a stamp of approval, which means different vendors will interact. Here a table about wireless tech’s which is shown on the presentation:

Wireless Technologies

  PAN
Personal Area Network		 LAN
Local Area Network		 MAN
Metropolitan Area Network		 WAN
Wide Area Network
Standards Bluetooth 802.11a, 802.11b, 802.11g, HiperLAN2 802.11 MMDS, LMDS GSM, GPRS, CDMA, 2.5 – 3G
Range Short Medium Medium to Long Long
Application Peer2Peer or Device to Device Enterprise Networks Fixed, Last Mile Access Mobile Phones, PDAs.

Chap 2: Radio Freq Spread Spectrum.
This chapter talks about radio transmission, mainly frequency modulation type stuff, points I’ve picked up….
Radio Frequencies are licensed, i.e. Radio & TV stations need licences to broadcast; the powers that be put aside a portion of the frequency spectrum for unlicensed use. The part that Cisco use is the ISM (Inductrial, Scientific & Medical) Frequencies. In the spectrum of frequencies, from low to high, where audio is at the low end, and light, x-rays etc. are at the higher, these frequencies are available to use:

  • 902 – 928 MHz & 26MHz
  • 2.4 – 2.4835 GHz & 83.5MHz
    IEEE 802.11b & 802.11g
  • 5GHz
    HyperLan, HyperLan2 & 802.11a

IEEE 802.11 is the industry standard for wireless lans, and it comes in 3 flavours:

  802.11b 802.11a 802.11g
Freq Band 2.4GHz 5GHz 2.4GHz
Availability World USA & Asia + Percific Wold
Max Data Rate 11Mbs 54Mbs 54Mbs
Sources of Interference Cordless Phone, Microwaves , Wireless Video or Bluetooth HyperLan Devices Same as .11b

Notice, that 802.11a isn’t available worldwide, so Cisco don’t use it so much in their products, 802.11g is the way forward ;)
A Note about the Laws of Radio Dynamics:

  • The Higher the Data Rate, the Shorter the Range (Distance)
  • The Higher the Power Output, The Longer the Range, the lower the Battery Life (Obviously)
  • The Higher the Radio Frequency, The Higher the Data Rate, but the Shorter the Range

RF Technologies is DATA sent over the air waves, with a primary goal of sending as much as quickley as possible.It is a half duplex technology, using the same frequency to send and recieve – devices take in turns, and because they use the ISM frequencies no Licenses are needed.
Different Spread Spectrum RF Technologies are:

  • FHSS (Frequency Hopping Spread Spectrum)
  • DSSS (Direct Sequence Spread Spectrum)
  • OFDM (Orthogonal Frequency Division Modulation)

Noise or Interference is caused by other transmissions; The further away you move from a transmission source, the more the noise interfers. Other factors that affect the transmission is the complexity of the modulation; The more complex the modulation, the shorter the distance away from the transmitter the noise begins to interfere… The more noise there is on a signal, the slower the data rate.

Simple Signal Modulation

Simple Signal Modulation

Signal Modulation is produced by the input of data and a carrier signal, the picture show’s (roughly/badly) what happens. Aironet devices have 3 type of modulations, and what is used depends on the data rate:

  • BPSK (Binary Phase Shift Keyed) for 1Mbs
  • QPSK (Quardrature Phase Shift Keying) for 2Mbs
  • CCK (Complementary Code Keying) or 5.5Mbs & 11Mbs

Direct Sequence Modulation in DSSS:
The data is broken into chunks, which can be send simultaneously down different channels. The chunks are combined with a chipping code – this is the chipping sequence, this special code allows one of the chunks to do missing (due to interference) and it’s contents can be calculated from the other chunks – a little like RAID5 I guess.

The DSSS 2.4Ghz can be boken into 11Channels of 22Mhz, but these overlap – there is a set of 3 Channels which don’t overlap, so different devices can use the same frequency with different channels so they don’t interfere with each other.

Note: The more data you want to send, the more bandwidth you need i.e. the more of the frequency spectrum you will need to use. This combined with the LAWS of RF , i.e. the further away from a signal you are the less bandwidth you have available causes a problem with Data Comms.
Cisco implement Rate shifting, this is where as your signal drops then so does your connection speed. In the case of 802.11b DSSS the stages are 11Mbs -> 5.5Mbs -> 2 Mbs -> 1Mbs.

From the above two paragraphs you can work out the maxium available bandwidth for 802.11b, assuming you were close enough to the AP, you could have 3 devices on different channels running at 11Mbs which is a total bandwith of 33Mbs :)

802.11b uses OFDM as it’s RF Technology, the main thing about this is it converts the frequency into sub carriers (or sub channels) if you use different modulation on these channels you get different speeds:

  • BPSK = 6 & 9 Mbs
  • QPSK = 12 & 18 Mbs
  • 16QAM = 24 & 36 Mbs
  • 64QAM = 48 & 54 Mbs

The 5GHz Range can be broken into 52 of the avilable 64 sub carriers, and 48 of those are used to transmit data (12 are used as zero side guards & 4 are used for sync + tracking) The 5GHz are broken into UNII Bands, what’s important is UNII 1 & UNII 2 are for inside use and UNII 3 is for out-doors !
Rate shifing in 802.11a is the same as in .11b other than there are more layers of bandwidth degredation.
802.11a has 8 channels avilable in it’s UNII bands. It also has different scaleability , 8 x 54 is 432Mbs of bandwidth but 802.11a doesn’t have as far range as 802.11b on the 2.5GHz frequency.

My 1st 100%

It’s a shame it’s not an important exam, but the satisfaction remains the same. I’m planning to make this year quite exam heavy so I don’t suppose I’ll see this again so excuse me as I revel in my own smugness !

I’ve been thinking hard (i.e. before I posted this), and really don’t think I’ve received 100% in a formal exam before; the results in the screen shot are for Cisco’s IOS Discovery Assessment, ok yeah there was only 13 questions but hey, 100% is 100% ;)

Debug Packet command missing on PIX 7

I’ve been googling & searching through cisco release notes to find out what happened to the pix debug packet command after I upgraded from v6.3 to v7, you know it really shouldn’t have taken that long because the first answer on google groups found it :$

The message suggest using the capture command and points to the cisco documentation : http://www.cisco.com/univercd/cc/td/doc/product/multisec/asa_sw/v_70/cref_txt/c.htm#wp1910869.

The first thing that strikes me is that the command isn’t a real time view like the old debug, but it will offer you a file that you can open in ethereal – now that’s quite cool :cool:
To get started you need to knock up an access list to capture the traffic, something like:

access-list sniffer permit ip host 192.168.1.1 host 192.168.2.2

should do the job, then start the capture on the interface where the traffic passes:

capture testcap access-list sniffer interface inside

before the next step you need to make sure you have the ADSM installed, and http server enable in your config, and a http line that allows you access, if you already use the ADSM you’re already set up, die hard ssh’ers like me need to set this up.

Once you’re happy adsm is running you can now browse to the results of you cap

https://securityappliance-ip-address/capture/capture_name

add a /pcap on the end if you want a version of the capture to load into ethereal.

You can use the no syntax to stop the capture

no capture testcap

Happy Debuggin’ !!!

A strange big warning when you upgrade pix 6.3 to 7

When it comes to cisco pix’s, I’m not a gui fan; the cisco command line is soo straight forward that I’ve never found the need for the PDM.

Anyway I came across a pix 6.3 with PDM installed that needed upgrading to v7, surprisingly this has to be done from the boot monitor, and after it was complete I was presented with this :

************************************************************************
**                                                                    **
**   *** WARNING *** WARNING *** WARNING *** WARNING *** WARNING ***  **
**                                                                    **
**          ----> Current image running from RAM only! < ----          **
**                                                                    **
**  When the PIX was upgraded in Monitor mode the boot image was not  **
**  written to Flash.  Please issue "copy tftp: flash:" to load and   **
**  save a bootable image to Flash.  Failure to do so will result in  **
**  a boot loop the next time the PIX is reloaded.                    **
**                                                                    **
************************************************************************

wow - this is different I thought, oh well had better follow the instructions, a copy tftp flash later, and all was happy.

As a side not you should notice that the PDM is now called the ADSM, and to install it the copy tftp flash:pdm has been dropped, and a normal copy tftp flash will work for the ADSM.

It's good to see that the ADSM works just as well in linux as it does in windows, the reporting graphs are pretty, but acl confif is still quicker in ssh ;)