A network can be defined as the interconnection of autonomous computers linked together to facilitate communication while networking is the simple concept of connected computers. Networks and networking have grown exponentially over the last 15 years; they have evolved at light speed just to keep up with huge increases in basic critical user needs such as sharing data and printers, as well as more advanced demands such as video conferencing.
Types of Networks
Local Area Network (LAN)
A LAN (Local Area Network) is a group of computers and network devices connected together, usually within the same building. A Local Area Network (LAN) is a high-speed communication system designed to link computers and other data processing devices together within a small geographical area, such as a workgroup, department, or building. Local Area Networks implement shared access technology. This means that all the devices attached to the LAN share a single communications medium, usually a coaxial, twisted pair or fibre optic cable.
Metropolitan Area Network (MAN)
Metropolitan area networks or MANs are large computer networks usually spanning a city or a town. They typically use wireless infrastructure or optical fibre connections to link their sites.
The IEEE 802-2001 standard describes a MAN as being: "A MAN is optimized for a larger geographical area than is a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate to high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of local networks. Metropolitan area networks can span up to 50km."
Wide Area Network (WAN)
Wide Area Network (WAN) is a computer network that covers a broad area. A WAN in compares to a MAN, is not restricted to a geographical location, although it might be restricted to a geographical locations, it might also be confined within the bounds of a state or country. A WAN connects several LANs, and may be limited to an enterprise (a corporation or organization) or accessible to the public. The technology is high speed and relatively expensive. The Internet is an example of a worldwide public WAN.
Routers are used to connect networks together and route packets of data from one network to another. Routers, by default break up a broadcast domain, which is the set of all devices on a network segment that hear all broadcasts sent on that segment. Routers also break up collision domains. This is an Ethernet term used to describe a network scenario where one particular device sends a packet on a network segment, forcing every other device on that segment to pay attention to it. At the same time, a different device tries to transmit, leading to a collision, after which both devices must retransmit one at a time.
Routers run on the layer 3 of the OSI (Open System Interconnection) reference model.
Switches are used for network segmentation based on the MAC addresses. Switches look at the incoming frame's hardware addresses before deciding to either forward the frame or drop it. Switches break up collision domains but the hosts on the switch are still members of one big broadcast domain.
A hub is really a multiple port repeater. A repeater receives a digital signal and re-amplifies or regenerates that signal, and then forwards the digital signal out all active ports without looking at any data. An active hub does the same thing. This means all devices plugged into a hub are in the same collision domain as well as in the same broadcast domain, which means that devices share the same bandwidth. Hubs operate at the physical layer of the OSI model.
IP AddressingAn IP address is a numeric identifier assigned to each machine on an IP network. It designates the specific location of a device on the network. An IP address is a software address and designed to allow host on one network to communicate with a host on a different network regardless of the type of LANs the hosts are participating in.
Bit: A bit is one digit, either a 1 or a 0.
Byte: A byte is 7 or 8 bits, depending on whether parity is used.
Octet: An octet, made up of 8 bits is just an ordinary 8 bit binary number. In most cases byte and octet are completely interchangeable.
Network address: This is the designation used in routing to send packets to a remote network. For example 10.0.0.0, 172.16.0.0, and 192.168.10.0 are network addresses.
Broadcast address: The address used by applications and hosts to send information to all nodes on a network is called the broadcast address. Examples include 255.255.255.255 which is all networks, all nodes; 172.16.255.255, which is all subnets and hosts on network 172.16.0.0.
Heirarchical IP Addressing Scheme
An IP address consists of 32 bits of information (IPV4). IPV6, a new version of IP consists of 128 bits of information. The 32 bits IP is divided into four sections referred to as octet or bytes each containing 1 byte (8bits).
An IP address is depicted using any of these three methods.
Dotted decimal, as in 172.16.30.56
Binary, as in 10101100.00010000.00011110.00111000
Hexadecimal, as in AC.10.1E.38
All these examples represent the same IP address. But the most commonly used is the dotted decimal. The Windows Registry stores a machine's IP address in hex.
The 32 bit IP address is a structured or hierarchical address, as opposed to a flat non hierarchical address. Although either type of addressing scheme could have been used, hierarchical addressing was chosen for a good reason. The advantage of this scheme is that it can handle a large number of addresses, namely 4.3 billion (a 32 bit address space with two possible values for each position that is either 1 or 0 gives 237, or 4,294,967,296).
The disadvantage of the flat addressing scheme relates to routing. If every address were unique, all routers on the internet would need to store the address of each and every machine on the internet. This would make efficient routing impossible.
Network Address Range
The network address uniquely identifies each network. Every machine on the same network shares that network address as part of its IP address. In the IP address of 172.16.30.56, 172.16 is the network address.
The node address is assigned to and uniquely identifies each machine on a network. This number can also be referred to as host address. In 172.16.30.56, 30.56 is the node address. Class A network is used when a small number of networks possessing a very large number of nodes are needed. Class C network is used when numerous networks with a small number of nodes are needed.
Class A Addresses
The first bit of the first byte in a class A network address must always be off or 0. This means a class A address must be between 0 and 127, inclusive.
If we turn the other 7 bits all off and then turn them all on, we'll find the class A range of network addresses.
00000000 = 0
01111111 = 127
Class A format is network.node.node.node, so for example in the IP address 22.214.171.124, the 49 is the network address and 22.102.70 is the node address. Every machine on this particular network would have the distinctive network address of 49.
Class B Addresses
The first bit of the first byte must always be turned on, but the second bit must always be turned off.
If we can turn the first bit on and the second bit off and if the other 6 bits all off and then all on, we'll find the class B range of network addresses.
10000000 = 128
10111111 = 191
Class B format is network.network.node.node, so far in the IP address 126.96.36.199, the 132.163 is the network address and 40.57 is the node address.
Class C Addresses
The first and second bit of the first byte must always be turned on, but the third bit can never be on.
If we turn the first and second bit on and the third bit off and then all other 5 bits all off and all on, we'll find the class C range of network address.
11000000 = 192
11011111 = 223
Class C format is network.network.network.node, for example in the IP address 188.8.131.52, the 195.166.231 is the network address and 75 is the node address.
Class D and Class E Addresses
The address between 224 and 255 are reserved for class D and E networks. Class D (224-239) is used for multicast addresses and class E (240-255) for scientific purposes.
Private IP Addresses
Private IP addresses are those that can be used on a private network, but they're not routable through the internet. This is designed for the purpose of creating a measure of well-needed security, but it also conveniently saves valuable IP address space. If every host on every network had to have real routable IP addresses, we would have run out of IP addresses to hand out years ago.
Class A 10.0.0.0 through 10.255.255.255
Class B 172.16.0.0 through 172.31.255.255
Class C 192.168.0.0 through 192.168.255.255
Troubleshooting IP Addressing
Here are the troubleshooting steps in resolving a problem on an IP network.
1. Open a DOS window and ping 127.0.0.1. This is the diagnostic or loopback address, and if you get a successful ping, your IP stack is considered to be initialized. If it fails, then you have an IP stack failure and need to reinstall TCP/IP on the host.
2. From the DOS window, ping the IP addresses of the local host. If that's successful, then your Network Interface Card (NIC) card is functioning. If it fails, then there is a problem with the NIC card. This doesn't mean that a cable is plugged into the NIC, only that the IP protocol stack on the host can communicate to the NIC.
3. From the DOS window, ping the default gateway. If the ping works, it means that the NIC is plugged into the network and can communicate on the local network. If it fails, then you have a local physical network problem that could be happening anywhere from the NIC to the gateway.
4. If steps 1 through 3 were successful, try to ping the remote server. If that works then you have IP communication between then local host and the remote server, you also know that the remote physical network is working.
5. If the user still can't communicate with the server after steps 1 through 4 were successful, then there's probably a resolution problem and there is need to check the Domain Name Server (DNS) settings.
Network Address Translation
Network Address Translation (NAT) is used mainly to translate private inside addresses on a network to a global outside address. The main idea is to conserve internet global address space, but it also increases network security by hiding internal IP addresses from external networks.
TABLE 3: NAT Advantages and Disadvantages
o Conserves legally registered addresses.
o Reduces address overlap occurrence.
o Increases flexibility when connecting to internet.
o Eliminates address renumbering as network changes.
o Translation introduces switching path delays.
o Loss of end-to-end traceability.
o Certain applications will not function with NAT enabled.
Types of NAT
Static NAT: This type of NAT is designed to allow one-to-one mapping between local and global addresses. Static NAT requires that there is one real internet IP address for every host on your network.
Dynamic NAT: This version gives one the ability to map an unregistered IP address to a registered IP address from out of a pool of registered IP addresses.
Overloading: This is also known as Port Address Translation (PAT). It is the most popular type of NAT configuration. Overloading is a form of dynamic NAT that maps multiple unregistered IP address to a single registered IP address by using different ports. With overloading thousands of users can connect to the internet using only one real global IP address.
Local addresses: Name of local hosts before translation.
Global addresses: Name of addresses after translation.
Inside local: Name of inside source address before translation.
Outside local: Name of destination host before translation.
Inside global: Name of inside hosts after translation.
Outside global: Name of outside destination host after translation.
Layer2 switching is the process of using the hardware address of devices on a LAN to segment a network. The term layer2 switching is used because switches operate on the data-link layer which is the second layer of the OSI reference model.
Layer2 switching is considered hardware-based bridging because it uses specialized hardware called an application-specific integrated circuit (ASIC). ASICs can run up to gigabit speeds with very low latency rates.
Switches read each frame as it passes through the network, the layer2 device then puts the source hardware address in a filter table and keeps track of which port the frame was received on. The information (logged in the switch's filter table) is what helps the machine determine the location of a specific sending device. After a filter table is built on the layer2 device, it will only forward frames to the segment where the destination hardware is located. If the destination device is on the same segment as the frame, the layer2 device will block the frame from going to any other segments. If the destination is on a different segment, the frame can only be transmitted to that segment. This is called Transparent Bridging.
When a switch interface receives a frame with a destination hardware address that isn't found in the device filter table, it will forward the frame to all connected segments. If the unknown device that was sent the frame replies to this forwarding action, the switch updates its filter table regarding that device's location.
Advantages of Layer2 Switching
The biggest benefit of LAN switching over hub-centred implementations is that each device on every segment plugged into a switch can transmit silmatenously whereas hubs only allow one device per network segment to communicate at a time.
Switches are faster than routers because they don't take time looking at the Network layer header information. Instead, they look at the frame's hardware address before deciding to either forward the frame or drop it.
Switches create private dedicated collision domains and provide independent bandwidth on each port unlike hubs. The figure below shows five hosts connected to a switch, all running 10Mbps half-duplex to the server. Unlike the hub, each host has 10Mbps dedicated communication to the server.
Limitations of Layer2 Switching
Switched networks break up collision domains but the network is still one large broadcast domain. This does not only limits your network's size and growth potential, but can also reduce its overall performance.
Functions of Layer2 Switching
There are three distinct functions of layer2 switching, these are:
o Address learning
o Forward⁄filter decision
o Loop avoidance
When a switch is first powered on, the MAC forward⁄filter table is empty. When a device transmits and an interface receives the frame, the switch places the frame source address in the MAC forward/filter table, allowing it to remember which interface the sending device is located on. The switch then has no choice but to flood the network with this frame out of every port except the source port because it has no idea where the destination device is actually located.
If a device answers the flooded frame and sends a frame back, then the switch will take source address from that frame and place that MAC address in its database as well, associating this address with the interface that received the frame. Since the switch now has both of the relevant MAC addresses in its filtering table, the two devices can now make a point to point connection. The switch doesn't need to flood the frame as it did the first time.
If there is no communication to a particular address within a certain amount of time, the switch will flush the entry from the database to keep it as current as possible.
When a frame arrives at a switch interface, the destination hardware address is compared to the forward⁄filter MAC database. If the destination hardware address is known and listed in the database, the frame is sent out only the correct exit interface.
The switch doesn't transmit the frame out any interface except for the destination interface. This preserves bandwidth on the other network segments and is called Frame Filtering.
When two switches are connected together, redundant links between the switches are a good idea because they help prevent complete network failures in the event one link stops working.
Redundant links are extremely helpful but they often cause more problems than they solve, this is because frames can be flooded down all redundant links silmatenously creating network loops.
Switches use a protocol called STP (Spanning Tree Protocol) created by Digital Equipment Corporation (DEC) now Compaq to avoid network loops by shutting down redundant links. With STP running, frames will be forwarded only on the premium STP-picked link.
This report exposes one to various aspects of computer networking, IP routing and IP switching and how to manage a network from an office network to larger networks. Areas covered in this report includes IP addressing, and Network Address Translation (NAT).
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