Network Certification Preparation

Module - 2 Types of cables Bridging and Switching Network segments using bridges, switches and routers Different types of LAN switching i.e. cut through, store and forward Spanning Tree Protocol – Operation and Benefits Virtual LAN – Describe and benefits Variable Length Subnet Mask – VLSM

Types of Cables Cable is the medium through which information moves from one network device to other. Cable types -Twisted Pair Cables -Unshielded Twisted Pair (UTP) Cable -Shielded Twisted Pair (STP) Cable - Coaxial Cable - Fiber Optic Cable

UTP Cables Categories CategorySpeedUse 11 MbpsVoice Only (Telephone Wire) 24 MbpsLocal Talk & Telephone (Rarely used) 316 Mbps10 Base T Ethernet 420 MbpsToken Ring (Rarely used) 5100 Mbps (2 pair)100 Base T Ethernet 5e1000 Mbps (4 pair)Gigabit Ethernet 610,000 MbpsGigabit Ethernet

STP Cables UTP cable is susceptible to radio and electrical frequency interference (it should not be too close to electric motors, fluorescent lights, etc.). Shielded cables can also help to extend the maximum distance of the cables. Shielded twisted pair cable is available in three different configurations: Each pair of wires is individually shielded with foil. There is a foil or braid shield inside the jacket covering all wires (as a group). There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).

Coaxial Cable It has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield. Difficult to install but is highly resistant to signal interference. Support greater cable lengths between network devices than TP cables. The two types of coaxial cabling are thick coaxial and thin coaxial. Thin coaxial cable : Also called thinnet or 10Base2. 2 refers to 200 meters but actually it is185 meters. Popular in school networks, especially linear bus networks. Thick coaxial cable : Also referred to as thicknet. or10Base5 5 refers to 500 meters. Has an extra protective plastic cover that helps keep moisture away from the center conductor. Better choice when running longer lengths in a linear bus network. Disadvantage of thick coaxial is that it does not bend easily and is difficult to install.

Fiber Optics Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals. Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. The cost of fiber optic cabling is comparable to copper cabling. More difficult to install and modify. 10 BaseF refers to the specifications for fiber optic cable carrying Ethernet signals. The center core of fiber cables is made from glass or plastic fibers A plastic coating then cushions the fiber center.

Switch An Ethernet switch is a device that provides a central connection point for cables from workstations, servers, and peripherals. Twisted-pair wire is run from each workstation to a central switch/hub. Most switches are active, means they electrically amplify the signal as it moves from one device to another. Modern switches build a port map of all IP address which respond on each port, and only broadcasts on all ports when it doesn't have a packet's target IP address already in its port map. Switches are: 8, 12, or 24, 48 RJ-45 ports and often used in a star /tree top Direct replacements for hubs, immediately reducing network traffic in most networks Usually installed in a standardized metal rack that also may store network servers, bridges, or routers Switches work at Layer 2 of OSI model

Bridge A bridge allows to segment a large network into two smaller, more efficient networks. A bridge monitors the information traffic on both sides of the network so that it can pass packets of information to the correct location. Most bridges can "listen" to the network and automatically figure out the address of each computer on both sides of the bridge. The bridge can inspect each message and, if necessary, broadcast it on the other side of the network. The bridge manages the traffic to maintain optimum performance on both sides of the network. It keeps information flowing on both sides of the network, but it does not allow unnecessary traffic through. Bridges can be used to connect different types of cabling, or physical media. They must use the same protocol on networks.

Router Routers select the best path to route a message, based on the destination address of the packet. Routers are the traffic directors of the global internet. All routers maintain complex routing tables which allow them to determine appropriate paths for packets destined for any address. Router connects two networks which may be using same or diff media types and protocols. The router can direct traffic to prevent head-on collisions, and is smart enough to know when to direct traffic along back roads and shortcuts. It works on Layer 3 of OSI model

LAN Switching Types Store-and-forward and Cut-through methods Both switches the packet based on SMAC. A store-and-forward switch makes a forwarding decision on a data packet after it has received the whole frame and checked its integrity. A cut-through switch engages in the forwarding process soon after it has examined the destination MAC (DMAC) address of an incoming frame. Cut-through switch receives and examines only the first 6 bytes of a frame, which carries the DMAC address

Spanning Tree Protocol Link management protocol that provides the path redundancy and avoid looping at layer 2 Spanning-Tree Protocol defines a tree that spans all switches in an extended network. Spanning-Tree Protocol forces certain redundant data paths into a standby (blocked) state Spanning-Tree Protocol operation is transparent to end stations All switches in an extended LAN participating in STP gather information about other switches in the network through an exchange of data messages. These messages are bridge protocol data units (BPDUs)

Spanning Tree Protocol An example network. The numbered boxes represent bridges (the number represents the bridge ID). The lettered clouds represent network segments d a b c f e

Spanning Tree Protocol - continue Each port on a switch using STP exists in one of the following five states: 1. Blocking 2. Listening 3. Learning 4. Forwarding 5. Disabled A port moves through these five states as follows: -From initialization to blocking - From blocking to listening or to disabled - From listening to learning or to disabled - From learning to forwarding or to disabled - From forwarding to disabled

Spanning Tree Protocol The smallest bridge ID is 3. Therefore, bridge 3 is the root bridge d a b c f e RP Root Bridge

Spanning Tree Protocol Assuming that the cost of traversing any network segment is 1, the least cost path from bridge 4 to the root bridge goes through network segment c. Therefore, the root port for bridge 4 is the one on network segment c. RP = Root Port d a b c f e RP Root Bridge

Spanning Tree Protocol The least cost path to the root from network segment e goes through bridge 90. Therefore the designated port for network segment e is the port that connects bridge 90 to network segment e. DP = Designated Port d a b c f e RP Root Bridge RP DP

Spanning Tree Protocol This diagram illustrates all port states as computed by the spanning tree algorithm. Any active port that is not a root port or a designated port is a blocked port. BP = Blocked Port d a b c f e RP Root Bridge RP DP BP

Virtual LAN (VLAN) A virtual local area network or VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same local area network regardless of their physical location. A VLAN has the same attributes as a physical local area network LAN), but it allows for end stations to be grouped together even if they are not located on the same network switch. VLAN membership can be configured through software instead of physically relocating devices or connections. VLANs are created to provide the segmentation services. VLANs address issues such as scalability, security, and network management.

Virtual LAN (VLAN) VLANs are layer 2 constructs, compared with IP subnets which are layer 3 constructs. In an environment employing VLANs, a one-to-one relationship often exists between VLANs and IP subnets, although it is possible to have multiple subnets on one VLAN. VLANs and IP subnets provide independent Layer 2 and Layer 3 constructs that map to one another and this correspondence is useful during the network design process.