Network Basics

Network Introduction

• A network is a collection of computers and other devices connected together so that they can communicate each other.
• In a network, connected devices can share files and peripherals such as modems, printers, tape backup drives, or CD-ROM drives etc..
• Connection medium is usually a wire (or cable), and also wireless communication between computers and peripherals is also possible.
• Each of the devices on the network can be thought of as a node and each node has a unique address.
  • Addresses are numeric quantities that are easy for computers to work with, but not for humans to remember.

    Example: 192.110.21.60
    

  • Some networks also provide names that humans can more easily remember than numeric numbers.

    Example: www.codingpointer.com
    This is corresponding to the numeric address mentioned above. 
    

• There are two types of network configuration, peer-to-peer networks and client/server networks.
• Networks interconnection is achieved using one or several of the following devices:
  • Bridge: is a device that links two different LANs based on the same protocol.
  • Router: is a communication device that connects different types of networks using different protocols.
  • B-router or Bridge/Router: is a single device that combines both the functions of bridge and router.
  • Gateway: is a network device that connects two different systems, using direct and systematic translation between protocols.
• Network Types:
  • Local Area Network(LAN) is usually confined to a limited geographic area, such as a single building or a college campus. LAN Technology – including Ethernet, Fast Ethernet, Gigabit Ethernet, 10 Gigabit Ethernet, ATM, PoE and Token Ring.
  • Wide area network(WAN) combines multiple LANs that are geographically separate and connecting the several LANs with dedicated leased lines such as a T1 or a T3, by dial-up phone lines (both synchronous and asynchronous), by satellite links and by data packet carrier services.
  • Wireless LANs, or WLANs, use radio frequency (RF) technology to transmit and receive data over the air. This minimizes the need for wired connections. WLANs give users mobility as they allow connection to a local area network without having to be physically connected by a cable.
  • Internet and its contributions to intranets and extranets.

Networking Basics

Ethernet

Ethernet is a networking protocol, specified by the IEEE 802.3 standard. Most wired network interface cards (NICs) communicate using Ethernet.

In an Ethernet network, the hosts connected to the network communicate by exchanging frames. Every host on an Ethernet network is uniquely identified by an address called the media access control (MAC) address.

VLANs

Subnets

IP addresses are broken up into two parts: a network number and a host identifier. Two hosts are on the same subnet if they have the same network number.

To find the network number from the IP address, needs to know the netmask associated with the IP.

A netmask indicates how many of the bits in the 32-bit IP address make up the network number.

There are two types to express a netmask:

• dotted quad: consider an IP address of 172.16.0.17, netmask would be written as 255.255.255.0
• classless inter-domain routing (CIDR): both includes IP address and netmask, example 172.16.0.17/24

DHCP

Hosts connected to a network use the Dynamic Host Configuration Protocol (DHCP) to dynamically obtain IP addresses. A DHCP server hands out the IP addresses to network hosts, which are the DHCP clients

IP

The Internet Protocol (IP) specifies how to route packets between hosts that are connected to different local networks. IP relies on special network hosts called routers or gateways.

In the OSI model of networking protocols IP occupies the third layer, known as the network layer.

TCP

Transmission Control Protocol (TCP) is the most commonly used layer 4 protocol in networked applications. TCP is a connection-oriented protocol: it uses a client-server model where a client connects to a server, where server refers to the application that receives connections.

UDP

User Datagram Protocol (UDP) is another layer 4 protocol that is the basis of several well-known networking protocols. UDP is a connectionless protocol: two applications that communicate over UDP do not need to establish a connection before exchanging data. UDP is also an unreliable protocol. The operating system does not attempt to retransmit or even detect lost UDP packets.

ICMP

Internet Control Message Protocol (ICMP) is a protocol used for sending control messages over an IP network.

Network components

Switches

Switches are Multi-Input Multi-Output (MIMO) devices to enable packets to travel from one node to another and connects the hosts that belong to the same layer-2 network. Switches are used to just forwarding of the packet received on one port (input) to another port (output).

Routers

Routers are special devices to enable packets to travel from one layer-3 network to another. Routers enable communication between two nodes on different layer-3 networks that are not directly connected to each other.

Firewalls

Firewalls are used to regulate traffic to and from a host or a network. A firewall can be either a specialized device connecting two networks or a software-based filtering mechanism implemented on an operating system

Load balancers

Load balancers can be software-based or hardware-based devices that allow traffic to evenly be distributed across several servers. By distributing the traffic across multiple servers, it avoids overload of a single server thereby preventing a single point of failure in the product. This further improves the performance, network throughput, and response time of the servers.