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IP Address Classes and Special IP Address Ranges.

Classes of IP addresses
TCP/IP defines five classes of IP addresses: class A, B, C, D, and E. Each class has a range of valid IP addresses. The value of the first octet determines the class. IP addresses from the first three classes (A, B and C) can be used for host addresses. The other two classes are used for other purposes (class D for multicast and class E for experimental purposes).

Classes of IP addresses:

Special IP address ranges: - addresses used to communicate with the current network - loopback addresses - link-local addresses (APIPA)
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Describe Local Area Network(LAN) & Metropolitan Area Network (MAN) With Example.

Local area network & Metropolitan area network

Local area network (LAN)
The term "local area network" is commonly used to describe a network of devices in a limited area (a house, office, building...). This type of network is usually capable of achieving high data transfer rate (up to 10 Gbps!) at low cost.

Some of the most popular LAN technologies are Ethernet, Token Ring and FDDI. Most LAN networks use TCP/IP to communicate. Twisted-pair cabling is usually used in a LAN.

Examples of this type of network are a small office network inside a single building or your home network.

Metropolitan area network (MAN)
The term „metropolitan area network“ is used to describe a network in a single metropolitan area, hence the name. This type of network is usually bigger than a LAN and smaller than a WAN. An example of this type of network would be a network that connects two company offices inside the same city.
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What is Wide Area Network (WAN) ? Difference Between LAN and WAN.

Wide area network :
The term „wide area network“ is used to describe a network that spans multiple geographic locations. Consider an example. A company has two offices, one in London and one in Berlin. Both offices have a LAN. If the company connects these two LANs together using WAN technology, a WAN is created.

Difference Between LAN and WAN.
The key difference between LANs and WANs is that the company usually doesn't own WAN infrastructure. A company usually leases WAN services from a service provider.

Frame Relay, ATM and X.25 are different types of WAN technologies. The Internet can also be considered a WAN.
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Describe Different Types of Network Cabling Like Coaxial Twisted-Pair and Fiber-Optic.

Types of Ethernet cabling
There are three cable types commonly used for Ethernet cabling: coaxial, twisted pair, and fiber-optic cabling. In today's LANs, the twisted pair cabling is the most popular type of cabling, but the fiber-optic cabling usage is increasing, especially in high performance networks. Coaxial cabling is generally used for cable Internet access. We will explain all three types of cabling. We will also explain a difference between a straight-through and crossover cable.

Coaxial cabling
Coaxial cable has an inner conductor that runs down the middle of the cable. The conductor is surrounded by a layer of insulation which is then surrounded by another conducting shield, which makes this type of cabling resistant to the outside interference. This type of cabling comes in two types, thinnet and thicknet. Both types have a maximum transmission speed of 10 Mbps. Coaxial cabling was used for computer networks, but today are largely replaced by twisted-pair cabling (Photo credit: Wikipedia)

Twisted-pair cabling
A twisted-pair cable has four pair of wires. These wires are twisted around each other to reduce crosstalk and outside interference. This type of cabling is common in most current LANs.

Twisted-pair cabling can be used for telephone and network cabling. It comes in two versions, UTP (Unshielded Twisted-Pair) and STP (Shielded Twisted-Pair). The difference between these two is that an STP cable has an additional layer of insulation that protects data from outside interferences.

Here you can see how a twisted pair cable looks like (Photo credit: Wikipedia):

A twisted-pair cable uses 8P8C connector, sometimes wrongly referred to as RJ45 connector (Photo credit: Wikipedia).

Fiber-optic cabling
This type of cabling uses optical fibers to transmit data in the form of light signals. The cables have strands of glass surrounded by a cladding material (Photo credit: Wikipedia).

This type of cabling can support greater cable lengths than any other cabling type (up to a couple of miles). The cables are also immune to electromagnetic interference. As you can see, this cabling method has many advantages over other methods but it's drawback is that it is the most expensive type of cabling.

There are two types of fiber-optic cables:
•    Single-mode fiber (SMF) - uses only a single ray of light to carry data
•    Multi-mode fiber (MMF) - uses multiple rays of light to carry data

Two types of connectors are commonly used:
•    ST (Straight-tip connector)
•    SC (Subscriber connector)
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Describe Network Devices. How Hubs Switches and Routers Work?

Hubs :
A hub serves as a central point to which all of the hosts in a network connect to. It is an OSI layer 1 device. It receives a signal from one port and sends it out to all other ports. Sometimes it is called a multiport repeater (photo credit: Wikipedia)

Today, these devices are considered obsolete and switches are commonly used instead. Hubs have numerous disadvantages. They are not aware of the traffic that passes through them. They create only one large collision domain. A hub typically operates in half duplex. There is also a security issue with hubs since the traffic is forwarded to all ports (except the source port), which makes it possible to capture all traffic on a network with a network sniffer!

Like hubs, a switch is used to connect multiple hosts together, but it has many advantages over a hub. Switch is an OSI Layer 2 device, which means that it can inspect received traffic and make forwarding decisions. Each port on a switch is a separate collision domain and can run in a full duplex mode (photo credit: Wikipedia).

How switches work : Let's take a look at the following example:

Host A is trying to communicate with Host B and sends a packet. A packet arrives at the switch, which looks at the destination MAC address. The switch then searches that address in its MAC address table. If the MAC address is found, the switch then forwards the packet only to the port that connected to the frame's destination. If the MAC address is not found, the switch will flood the frame out all other ports. To learn which MAC address is associated with which port, switches examine the source MAC addresses of the receiving packet and store that MAC addresses in their MAC address table.

What is a MAC address table?
A MAC address table lists which MAC address is connected to which port. It is used by switches to make forwarding decisions. The table is populated by examining the source MAC address of the incoming packet. If the source MAC address of a packet is not present in the table, the switch adds an entry to it's MAC address table. The picture below show how a MAC address table on a switch looks like:

Difference between a switch and a bridge
A switch is sometimes called a multiport bridge, but there are differences between these two devices. A bridge usually has fewer ports than switch. A switch operates faster because it is hardware-based, which means that it uses chips (ASICs) when making forwarding decisions. In contrast, a bridge is software based. A switch can also have multiple spanning-tree instances while a bridge can have only one. Switches can also have multiple broadcast domains, one per VLAN.

A router is a device that routes packets from one network to another. A router is most commonly an OSI Layer 3 device. Routers divide broadcast domains and have traffic filtering capabilities.

The picture below shows a typical home router:

How routers work

A router uses IP addresses to figure out where to send packets. If two hosts from different networks want to communicate, they will need a router between them to route packets

For example, check the following scenario:

Host A and host B are on different networks. If host A wants to communicate with host B, it will have to send a packet to the router. The router receives the packet and checks the destination IP address. If the destination IP address is in the routing table, the router will forward the packet out the interface associated with that network.

What is a routing table?
A routing table lists a route for every network that a router can reach. It can be statically configured (using IOS commands) or dynamically learned (using a routing protocol). It is used by routers when deciding where to forward packets.

The picture below shows how a routing table looks like:

The command to display an IP routing table is show ip route. In the picture above, you can see that this router has two directly connected subnets. Let's take a closer look at the first entry in the routing table:

„C“ means that the route is a directly connected route. The network in question is, and the router will forward each packet destined for that network out interface FastEthernet0/1.

NOTE – in Windows, you can use the netstat –r command to display the routing table of your system.
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