GUESSOUM: NETWORKING ET CISCO SITE

1-THE LAYERED MODEL   2- THE OSI MODEL            3-TYPES OF MEDIUM 

4-IP ADDRESSING         5-PASSWORD RECOVERY  

cours 1:           The layered network model

 Network models use layers to simplify the networking functions.
 The separation of  networking functions is called layering. To
 understand the importance of layering, let's consider the OSI
 reference model, a layered  model for understanding and implementing
 computer communications. By using layers, the OSI reference model
 simplifies the tasks  required for two computers to communicate
 with each other.  

 Each layer can be focused on specific  functions, thereby allowing
 the networking  designer to choose the right networking  devices
 and functions for the layer. In the OSI  reference model, each of
 the seven numbered  layers indicate distinct functions. The reasons
 for this division of network functions include  the following:  

     .Layers divide the aspects of network
      operation into less complex elements. 
     .Layers define standard interfaces for
      plug-and-play compatibility. 
     .Layers enable engineers to specialize
      design and development efforts on
      modular functions. 
     .Layers promote symmetry in the
      different network modular functions so
      that they work together. 
     .Layers prevent changes in one area
      from affecting other areas, so each
      area can evolve more quickly. 
     .Layers divide the complexity of
      networking into separate, easy to learn
      operations. 
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cours 2:          The OSI model

The OSI model consists of seven layers, each of which can
(and typically does) have several sublayers.
       
         The upper layers of the OSI model 
(application, presentation, and session-Layers 7, 6, and 5)
are oriented more toward services to the applications. 

        The lower four layers 
(transport, network,data link, and physical-Layers 4, 3, 2, and 1) 
are oriented more toward the flows of data from end to end through 
the network.

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cours 3:	    	Types of Medium (Types de cables )

Unshielded Twisted Pair (UTP) Cable:


              
   The quality of UTP may vary from telephone-grade wire to extremely 
   high-speed cable. The cable has four pairs of wires inside the jacket. 
   Each pair is twisted with a different number of twists per inch 
   to help eliminate interference from adjacent pairs and other electrical 
   devices. The tighter the twisting, the higher the supported transmission 
   rate and the greater the cost per foot. The EIA/TIA (Electronic 
   Industry Association/Telecommunication Industry Association) has 
   established standards of UTP and rated five categories of wire. 
              
              Categories of Unshielded Twisted Pair

              Type                        Use
              Category 1       Voice Only (Telephone Wire)
              Category 2       Data to 4 Mbps (LocalTalk)
              Category 3       Data to 10 Mbps (Ethernet)
              Category 4       Data to 20 Mbps (16 Mbps Token Ring)
              Category 5       Data to 100 Mbps (Fast Ethernet)

Unshielded Twisted Pair Connector (RJ-45 connector):

   The standard connector for unshielded twisted pair cabling is an 
   RJ-45 connector. This is a plastic connector that looks like a large 
   telephone-style connector (See fig. 2). A slot allows the RJ-45 
   to be inserted only one way. RJ stands for Registered Jack, implying 
   that the connector follows a standard borrowed from the telephone 
   industry. This standard designates which wire goes with each pin 
   inside the connector. 
              

  Fig. 2. RJ-45 connector 
             
Coaxial Cable & Connectors:

   Coaxial cabling has a single copper conductor at its center. A plastic 
   layer provides insulation between the center conductor and a braided 
   metal shield (See fig. 3). The metal shield helps to block any outside 
   interference from fluorescent lights, motors, and other computers. 
              

   Fig. 3. Coaxial cable            Fig. 4. BNC connector
            
Fiber Optic Cable:

   Fiber optic cabling consists of a center glass core surrounded by 
   several layers of protective materials (See fig. 5). It transmits 
   light rather than electronic signals eliminating the problem of 
   electrical interference. This makes it ideal for certain environments 
   that contain a large amount of electrical interference. It has also 
   made it the standard for connecting networks between buildings, 
   due to its immunity to the effects of moisture and lighting. 
         

     Fig.5. Fiber optic cable

               Ethernet Cable Summary:
              
   Specification         Cable Type                 Maximum length
     10BaseT      Unshielded Twisted Pair             100 meters
     10Base2      Thin Coaxial                        185 meters
     10Base5      Thick Coaxial                       500 meters
     10BaseF      Fiber Optic                         2000 meters
     100BaseT     Unshielded Twisted Pair             100 meters
     100BaseTX    Unshielded Twisted Pair             220 meters
           
Wireless LANs:

   Wireless LANs use high frequency radio signals, infrared light beams, 
   or lasers to communicate between the workstations and the file server 
   or hubs. Each workstation and file server on a wireless network 
   has some sort of transceiver/antenna to send and receive the data. 
   Information is relayed between transceivers as if they were physically 
   connected. For longer distance, wireless communications can also 
   take place through cellular telephone technology,microwave transmission, 
   or by satellite. Wireless LANs have several disadvantages. They 
   are very expensive, provide poor security, and are susceptible to 
   interference from lights and electronic devices. They are also slower 
   than LANs using cabling.

Vocabulary:
           
   DHCP - (Dynamic Host Configuration Protocol) A protocol that is 
           run on a server that assigns one or all of the following to a 
           TCP/IP client: IP address, subnet (mask), default gateway, 
           DNS servers'IP addresses.
   NAT - (Network address translation) Multiplexes traffic from the 
         internal network and present it to the Internet as if it was 
         coming from a single computer having only one IP address.
   MicroSegmentation - Division of a network into smaller segments, 
         usually with the intention of increasing aggregate bandwidth to 
         network devices.
   Collision Domain - In ethernet, the network area within which frames 
              that have collided are propagated. Repeaters and hubs
              propagate collisions.
                                  
Installing Cable - Some Guidelines:
              
   When running cable, it is best to follow a few simple rules:
     · Always use more cable than you need. Leave plenty of slack. 
              
     · Test every part of a network as you install it. Even if 
       it is brand new, it may have problems that will be difficult to 
       isolate later. 
     · Stay at least 3 feet away from fluorescent light boxes 
       and other sources of electrical interference. 
     · If it is necessary to run cable across the floor, cover 
       the cable with cable protectors. 
      · Label both ends of each cable. 
      · Use cable ties (not tape) to keep cables in the same location 
        together. 

Easy steps for creating patch cables:
              
   When you are making a specific kind of connection it requires a 
   certain type of cable configuration. Patch cables are cables that 
   have standard connectors, often referred to as RJ-45 connectors, 
   on both ends of the cable. Although there are a many variations 
   of patch cables, there are three patch cable standard configurations 
   that are common in the industry.
      · Straight-through cables: Used to connect end systems to 
        wall jacks, and active devices to patch panels ports (i.e. hubs, 
        switches, etc)
      · Cross connect cables (a.k.a. cross-over): Used for connecting 
        two hubs/switches together or two active devices together.
      · Roll Over cables: Many manufacturers use roll over cables 
        to connect a computer to the console port of a router, switch,
        bridge or hub for management purposes. The configuration listed
        in this document works with all cisco devices. For other
        manufacturers refer to the specifications listed in their
        documentation.

      1. Cut the desired length of cable and typically leave a small amount 
              of slack.
      2. Take the cable and strip off the sheath at each end (about 1 
         ½ inches so you can manipulate the wires
      3. Separate out each pair of wires (so it resembles a fan).
      4. Using the charts below, arrange each individual wire and line 
         them up correctly, side by side, as close as possible with the 
         left most wire being the one to go in the left most slot of the 
         connector.This takes practice so be patient, and be sure to do 
         only one side of the cable at a time.
           


           
           
      5. After, you have lined each of the wires according to the numbering 
         scheme, slide them into the connector (RJ-45 connector).The 
         connector should always have the copper lines facing upwards, 
         and the open end facing toward you. [hint: Inserting the wires
         with a little downward pressure helps spread the wires out and
         slide into the slots easier]
      6. The wires must be inserted all the way so the copper tips can 
         be seen clearly from the front end of the connector (the tips are 
         butted up tightly against the end of the slot). The sheath should 
         be inside the connector about ¼ inch.
      7. Now you have to crimp the wires using a Crimper tool. This is 
         completed by inserting the connector into the slot of the Crimper 
         tool (usually with the flap pointed downwards), and tightly
         squeezing the handles together.
      8. Complete steps 1-7 for the other side of the cable "Connector B".
      9. Use a cable tester to test if your connections are correct.
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 cours 4:	    	IP addressing





Classes of Networks

Class A, B, and C networks provide three network sizes. By definition, 
all addresses in the same network have the same numeric value network 
portion of the addresses. The rest of the address is called the host
portion of the address. Individual addresses in the same network all 
have a different value in the host parts of the addresses but have 
identical values in the network part.



Network numbers look like addresses (in dotted decimal format),
but they are not assignable to any interface as an IP address. 
Conceptually, network numbers represent the group of all 
IP addresses in the network. Numerically, the network number
is built with a nonzero value in the network part but with
all 0s in the host part of the network number.







IP Grouping Concepts and Subnetting
  Subnetting is simply the process of treating subdivisions of
a single Class A, B, or C• IP protocols enforce the following 
grouping concept: All hosts in the same group must not be 
separated by an IP router. A corollary to the grouping concept 
is this: Hosts separated by an IP router must be in separate 
groups.The mask defines the number of host bits in the host part 
of an address.


  The example shows that the subnet field consists of bits 
17 through 24 (the entire third byte).150.150.2.1 and 150.150.2.2 
are in the same subnet because they are in the same Class B network
and because their subnet fields have the same value (0000 0010).
150.150.4.2 is in a different subnet of the same Class B network
because the subnet field has a different value than the first two
addresses (0000 0100). 150.150.4.2 must be physically located with at
least one IP router between itself and 150.150.2.1 and 150.150.2.2.
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 cours 5:	    	password recovery
 



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