Networks Basics

C Viven Rajendraviven@cse.iitb.ac.in

Contents

• What is a network?

• How does it work?

• HUB, Switch, Router.

• Classifying network.

• Proxy, IP, Subnet, DNS.

• WiFi, netmon, simple applications.

Computer Network

• A computer network is a group of interconnected “network capable devices”.

• Components : Network Interface Cards, Hubs, Switches, Routers and galvanic cable.

How does it work?• What is communicated?

• When is it communicated?

• How is it communicated?

• Example : Talking, torch light communication.

• We need a protocol : Set of rules governing data

communication.

• TCP/IP is such a protocol.

Basic Hardware Components

• Network Interface Card (NIC)• Hub• Switch• Router• Cable

Network Interface Card

• Allows a network capable device access to a computer network such as the internet.

• The MAC address identifies the vendor and the serial number of the NIC which is unique to the card.

Hub

• A network hub or repeater hub is a device for connecting multiple twisted pair or fiber optic Ethernet devices together.

• When a packet arrives at one port, it is copied to all the ports of the hub for transmission

Switch

• A switch is a device that performs switching.

• It forwards and filters datagrams (chunk of data communication) between ports based on the Mac-Addresses in the packets.

Router

• Forward data packets between networks using headers and forwarding tables to determine the best path to forward the packets.

• Processor, OS, memory.

Router

Cables

• Category 5 cable, known as Cat 5 or "Cable and Telephone", is a twisted pair cable.(100 Mbps)

• An optical fiber is a glass or plastic fiber that carries light along its length.(40 Gbps)

Classifying Networks

• On the basis of scale or extent of reach of network :

LAN, MAN, WAN.

• On the basis of connection method : hardware

technology : Optical fibre, Ethernet, Wireless LAN.

• Functional relationship: Client-Server, Peer-to-peer.

• On the basis of network topology, Physical layout:

Mesh, Star, Bus, Ring, Hybrid

Local Area Network (LAN)

• Most current LANs run on Ethernet and use the IEEE 802.3 protocol for communication.

• IITB LAN is a very good example.

• Large computer networks usually spanning a city.

Metropolitan Area Network

Wide Area Network (WAN)

WAN (contd..)

• Covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries).

• The largest and most well-known example of a WAN is :

Networking basics

• What is a Proxy?• What is an IP address?• What is subnet mask?• What is Default gateway?• Domain Name System (DNS)

Proxy

• Interface between internal and external network(Internet)

• Primary advantages: – Security (from outside)– Access control ( sites, virus)– Efficient network utilization due to caching

Proxy configuration in browsers

• Institude wide : netmon.iitb.ac.in• Port 80 for netmon• LDAP username & password for netmon• Proxy not required for

– *.iitb.ac.in– 10.0.0.0/8

• Automatic proxy configuration URL: – http://www.cc.iitb.ac.in/autoproxy.pac

Proxy configuration in browsers

Proxy configuration in browsers

Proxy configuration in browsers

IP address• An Internet Protocol (IP) address is a numerical

identification that is assigned to devices participating in a computer network utilizing the Internet Protocol for communication between its nodes.

• The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255.

• Mine is 10.2.201.72

Subnet mask

• A portion of the network's computers and network devices that have a common, designated IP address routing prefix.

• A mask used to determine what subnet an IP address belongs to.

• An IP address has two components, the network address and the host address

• Hostel-2 subnet is 255.255.0.0, so allowed ip-addresses are 10.2.xxx.xxx

Default gateway

• A node (a router) on a computer network that serves as an access point to another network.

• Viewed simply as an entry point and an exit point in a network.

• A default gateway is used by a host when an IP packet's destination address belongs to someplace outside the local subnet.

• Hostel-2 has a computer : 10.2.250.1

Default gateway contd..

Domain Name System (DNS)

• Associates various information with domain names;

• It serves as the "phone book" for the Internet by translating human-readable computer hostnames, e.g. www.google.com, into IP addresses, e.g. 208.77.188.166, which networking equipment needs to deliver information

DNS Example

Suggested Material

• Kurose, Ross : Computer Networking: A Top-Down Approach.

• WikiPedia – Computer Network : http://en.wikipedia.org/wiki/Computer_network

• Subnet mask : http://www.tech-faq.com/subnet-mask.shtml

Demo

• SSH• Putty• Secure shell• Pine• IITB newsgroup

Thank You