Networking & Fundamentals

Networking and its fundamentals

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Outline • • • • • • •

What is network? Basic requirements of a network Components of a network Protocols Classification of computer networks TCP/IP protocol stack Applications

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What is a network? • A computer network is "A set of data processing nodes that are interconnected for the purpose of data communication".

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Basic requirements for a network • In order for a network to function, it must meet three basic requirements: – It must provide connections • Connection refers to the hardware.

– It must provide communications • Communication is the way in which the devices talk to each other.

– It must provide services • Services are the things which are shared with the rest of the network. CORAL TELECOM LTD.

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Components of network • • • • •

Message Sender Receiver Protocol Medium

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Protocols • Set of rules governing data communication. • Integration of three basic functions: – What is communicated? – How is it communicated? – When is it communicated?

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Classification of computer networks • On the basis of scale or extent of reach of network – LAN, MAN, WAN

• On the basis of connection method – hardware technology: Wired, Wireless, Hybrid

• On the basis of functional relationship – Client-Server, – Peer-to-peer

• On the basis of network topology – Physical layout: Mesh, Star, Bus, Ring, Hybrid CORAL TELECOM LTD.

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Local Area Network • In general privately owned, which covers a small area • Network in a building

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Metropolitan Area Network • Extends over an entire city • It may be a single network or a means of connecting a number of LANs together.

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Metropolitan Area Network

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Wide area network • Generally covers a country, a continent and can be extended to the whole world • Example: Internet

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Mesh network • Point to point dedicated link between any two nodes • Elimination of traffic problem • Provides security and privacy of data • Robust • Not Scalable – Interface problem

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Mesh network

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Star network • Each node is connected to the central controller. • It does not allow direct traffic between devices. • Robust, provided the controller remains active • Scalable

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Star network

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Bus network • One long cable act as a backbone to link all the devices in a network. • Nodes are connected to bus cable by the drop lines and taps. • No security and privacy to data. • Broadcasting of data

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Bus network

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Ring network • Each device has a dedicated point to point connection only to the two devices on either side of it. • No broadcasting of data. • Scalable

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Ring network

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TCP/IP Protocol Stack

Fig.: TCP/IP Stack CORAL TELECOM LTD.

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Physical Layer • Task – Transmit raw bits over communication channel

• Fundamental unit of transfer: Bit • Examples – – – – –

Twisted pair Coaxial cable Optical fiber cable Radio transmission Microwave transmission

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Physical Layer – Example

Fig.: Physical Layer Example

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Data Link Layer • Task – Provide raw transmission across a link – Error detection and correction – Flow control

• Fundamental unit of transfer: Frame • Example – Protocols such as HDLC and PPP

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Data Link Layer Example

Fig.: Data Link Layer Example CORAL TELECOM LTD.

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Network Layer • Task – Host to host delivery – Routing – Congestion control

• Fundamental unit of transfer: Packet • Example – IP

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Network Layer – Example

Fig.: Network Layer Packet Transfer CORAL TELECOM LTD.

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Internet Protocol - IP

Fig.: IP Addressing CORAL TELECOM LTD.

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IP Example

Fig.: IP Addressing Example

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Transport Layer • Task – Process to process message delivery

• Fundamental unit of transfer: TPDU • Examples – TCP (Transmission Control Protocol) – UDP (User Datagram Protocol)

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Transport Layer Example

Fig.: Transport Layer Functioning CORAL TELECOM LTD.

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Application Layer • Task – Provides services to users

• Fundamental unit of transfer: Message • Examples – WWW – Email – Chat – Multimedia streaming CORAL TELECOM LTD.

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Layering – Physical Communication data application transport network link physical application transport network link physical

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network link physical

application transport network link physical 32

data application transport network link physical

Domain Name System DNS • Task – To resolve host name

• Internet name space – Over 200 domains: Generic and Countries – Sub domains – Hosts

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Accessing Website

Fig.: Path for www.iitb.ac.in CORAL TELECOM LTD.

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Accessing Website 3 2 8

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9 7

1 10

5 6

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Fig.: Looking up www.iitb.ac.in CORAL TELECOM LTD.

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Networking Devices • HUB • Bridge • Switch • Router

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Switching is done on the basis of the source and destination Ethernet addresses

Switching is done, based on the IP address of the endpoints

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Questions • What is difference between IP address and Ethernet Address? • What is a Public and Private IP? • How is data sent over internet? • How are IP addresses allocated to my PC? • What is difference between switch and router? CORAL TELECOM LTD.

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Questions • • • •

What is a layer 2 switch? Where and why do we use NAT? What is the significance of subnet mask? What is the difference between broadcast and Multicast? • What is streaming?

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IP Addresses • 32 bits in existing IP (IPv4), 128 bits in IPv6 (future). • Typically written in form xxx.xxx.xxx.xxx (e.g. 192.168.0.1) • Binary Representation: 11000000

10101000

00000000

00000001

• Logical Identification of a system in a network CORAL TELECOM LTD.

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IP Addresses • Hierarchical Division in IP Address: 

Network Part (Prefix)  describes which physical network



Host Part (Host Address)  describes which host on that network 192

168

0

1

11000000

10101000

00000000

00000001

Network

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Host

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Subnet Mask • Define which bits are used to describe the Network Part and which for hosts • Different Representations: – – – –

decimal dot notation: 255.255.255.0 binary: 11111111 11111111 11111111 00000000 hexadecimal: 0xFFFFFF00 number of network bits: /24

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Subnet Mask • For E.g. IP IP (Binary)

192

168

0

1

11000000 10101000 00000000 00000001

Netmask

255

255

255

0

(Binary)

11111111

11111111

11111111

00000000

Network

Host

• All 0’s in host part: Represents Network – e.g. 192.168.0.0/24

• All 1’s in host part:

Broadcast

– e.g. 192.168.0.255 (192.168.0.0/24)

• 127.0.0.0/8: Loopback address (127.0.0.1) CORAL TELECOM LTD.

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Allocating IP Addresses • The Subnet mask is used to define size of a network • E.g. a subnet mask of 255.255.255.0 or /24 implies 3224=8 host bits – 2^8 minus 2 = 254 possible hosts

• Similarly a subnet mask of 255.255.255.224 or /27 implies 32-27=5 hosts bits – 2^5 minus 2 = 30 possible hosts

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Public / Private IP Addresses • Public IP • Private IP • Public IP allotted by a world body – unique all around the world • Unlike public IP, private IP addresses are not valid on the Internet. • Range of Private IP addresses: – 10.0.0.0 to 10.255.255.255 – 172.16.0.0 to 172.31.255.255 – 192.168.0.0 to 192.168.255.255 CORAL TELECOM LTD.

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MAC Address • MAC Address – Media Access Control Address – A hardware address that uniquely identifies each node of a network • 48 – bit address • MAC Address are also called as Ethernet Address • MAC address are unique and they are allotted by the manufacturer of the Ethernet device • MAC address cannot be modified by the user CORAL TELECOM LTD.

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Router • A specialized device (computer) connected to more than one to transfer data packets from one network to another. • IP networks are packet-switched networks, which means that the packets can take different routes between a source and a destination host. • The whole Internet consists of a number of networks connected to each other via routers.

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Functions of Router • Routers operate at the Network Layer (OSI layer 3) • Layer 3: Network layer (e.g. IP) – Unreliable • if packet gets lost, network layer doesn’t care • higher layers can resend lost packets

– Forwards packets hop by hop

OSI Model Layers 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

• receive from one link, forward to another link • There can be many hops from source to destination • Packet-switched networks, packets can take different routes between a source and a destination host. 47

Functions of Router • Layer 3: Network layer (e.g. IP) – Makes routing decisions • how can the packet be sent closer to its destination? • routers can talk to each other to exchange information about network topology

• The addresses used by the IP protocol are 32-bit numbers. • IP addresses are split up into four 8-bit numbers called octets. For example, 193.12.15.1.

OSI Model Layers 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

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Router (Example) •

•

•

The first networks is identified by the IP-number 193.12.15.0 and the other network is identified by the IP-number 10.5.17.0. On every network there are two hosts. Observe that the first three octets in the IP-numbers are the same as in the IP-number of the networks. The router that connects the two networks has two interfaces with IP-numbers that belong to each respective network.

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Routing Decision •

The router algorithm includes four different steps. –

–

–

–

The first question is if the destination host is on a network that is directly connected to the router. If the answer to this question is yes the router makes a direct delivery to the destination host. Otherwise the next question is if the destination host is to be found in the routing table. If the answer is yes, then the router sends the packets to a router that is closer to the destination host. Otherwise the router looks to see if the network, to which the destination host is connected, is to be found in the routing table. If the answer is yes, then the router sends the packets to a router that is closer to the destination host. The last chance for the router is to use a default router to send the packet to. Now it is up to the default router to find the destination host. The default router is sometimes also called the default gateway.

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Routing Table • •

•

How does the router choose where to send the packets? The router keeps the routing information in a table. This information tells the router how to reach remote networks and hosts. A catchall entry, also called the default router must generally be supplied. All packets to an unknown network or host are sent to the default router. In the picture you see a router with its specific routing table. If the packets are to be delivered to the host with IP-number 192.1.5.10, the router sees that the destination host belongs to the network 192.1.5.0. The routing table says that this network can be reached via the router 192.1.8.2.

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Administrative Distances • The administrative distance (AD) is used to rate the trustworthiness of routing information received on a router from a neighbor router. • An administrative distance is an integer from 0 to 255, where 0 is the most trusted and 255 means no traffic will be passed via this route. • Lowest AD will be placed in the routing table

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Static Routing • Static routing is the term used to refer to the manual method used to set up routing. • Static Route has default administrative distance of 1 • Advantages: – Easy to predict and understand in small networks – Simple to setup

• Disadvantages: – An administrator enters routes into the router using configuration commands. – Requires extensive planning and has a high management overhead – When there is a change in the network or a failure occurs between two statically defined nodes, traffic will not be rerouted. 53

Dynamic Routing (Routing Protocols) • Routing protocols are used so that the routers in a network can learn things from other routers automatically. • Routing protocols are used when we have many different routers – if one link goes down, the routing protocol can teach other routers in the network a new way to the destination.

• No need for routing protocols in Point-to-Point network with no alternative routes. – Routing protocols just give you a lot of ”overhead” traffic in your network.

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Routing Protocols •

Two groups of routing protocols: –

–

•

Three examples of IGP protocols are: – –

–

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Interior Gateway Protocol, IGP which is used inside a local network. This network is also called an autonomous system or AS. Exterior Gateway Protocols, EGP, and is used between autonomous systems. EGP, is normally used by the Internet service providers.

RIP, which stands for Routing Information Protocol. IGRP, which stands for Interior Gateway Routing Protocol and EIGRP, which stands for Enhanced Interior Gateway Routing Protocol and they are two Cisco specific protocols. OSPF, which stands for Open Shortest Path First.

Two examples of EGP routing protocols are: – –

BGP, which stands for Border Gateway Protocol. GGP, which stands for Gateway to Gateway protocol. This protocol is history and is not used today.

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RIP (Routing Information Protocol) • Distance vector routing protocol, The distance-vector protocols find the best path to a remote network by judging distance. • RIP is stable, widely supported, and easy to configure • RIP uses hop count metric to measure distance, it only takes into consideration the number of routers you need to pass in order to reach the destination host. This is called the cost to reach the destination host. • RIP does not take into account the quality or bandwidths of the connected links.

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RIP (Routing Information Protocol) • RIP broadcasts its routing table every 30 seconds in order to share with other routers. This gives a lot of overhead traffic on the network. • The maximum number of hops in a path is 15. • If increasing the metric value by 1 causes the metric to be infinity (that is, 16), the network destination is considered unreachable. • RIP has default Administrative Distance value of 120

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RIP V 1/2 • RIP version 1 uses only classful routing, which means that all devices in the network must use the same subnet mask. • RIP version 1 doesn’t send updates with subnet mask information in tow. • RIP version 2 provides something called prefix routing, and does send subnet mask information with the route updates. This is called classless routing.

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RIP (Example) •

This picture shows three routers using RIP. The router B, for example was originally configured with the information about the directly connected networks. The rest of the information in the routing table has been learned from the other routers in the network.

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OSPF-Open Shortest Path First • Based on Dijkstra’s algorithm, first, a shortest path tree is constructed, and then the routing table is populated with the resulting best paths. • Link-state protocol, also called shortest-path-first protocols

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OSPF-Open Shortest Path First • Uses link state routing strategy – Each router keeps list of state of local links to network. – Transmits update state information to all other routers within the same area.

• Route computed on least cost based on user cost metric.

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OSPF-Network Hierarchy • OSPF is supposed to be designed in a hierarchical fashion, which basically means that you can separate the larger internetwork (AS) into smaller internetworks called areas. • OSPF must have an area 0 called Backbone Area, and all routers should connect to this area if at all possible • Routers that connect other areas to the backbone within an AS are called Area Border Routers (ABRs). • An area’s topology is invisible to entities outside the area. • OSPF backbone is responsible for inter area communication. It consists of all Area Border Routers, networks not wholly contained in any area, and their attached routers. • An ASBR is a router that is connected to more than one AS and that exchanges routing information with routers in other ASs. ASBRs typically also run a non-IGP routing protocol (e.g., BGP), or use static routes, or both. An ASBR is used to distribute routes received from other ASs throughout its own AS.

OSPF Design Example

OSPF-Features • OSPF provides the following features: – – – – – –

Consists of areas and autonomous systems Minimizes routing update traffic Allows scalability Supports VLSM/CIDR Has unlimited hop count Allows multi-vendor deployment (open standard)

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Redundancy •

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Redundancy means having more than one possible path to reach the destination host. In the picture you can see that there are two alternative ways between the host A and host B which gives us redundancy. On the Internet for example, there are many alternative ways to reach a host or a network, which means that Internet has a lot of redundancy.

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Dynamic Update •

•

To use all the benefits of a secure and redundant network structure a routing protocol is needed. The routing protocol must be used so that the routers can exchange information continuously about the status of the links between the different routers. This means that the router information is dynamically updated. In the picture you can see that a path between routers has been broken. With the help of routing protocols the information about the broken link is sent to other routers in the network. This means that the routers will send the packets using an alternative path.

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Some Terminologies • DHCP - Dynamic Host Control Protocol – DHCP automatically configures the PC's IP address, the gateway address and also the DNS address

• DNS - Domain Name Service – used to map domain names (e.g. www.coraltele.com) to IP address and vice-versa

• NAT – Network Address Translation – networking protocol that allows network of private IP address to be set up using a single Public IP address

• Gateway – a network point that acts as an entrance to another network

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Some Terminologies • Broadcast – Packets are transmitted to all user terminals in a network

• Multicast – Packets transmitted to selected multiple recipients who have joined the appropriate multicast group.

• Unicast – Packets transmitted to a single user.

• Streaming – Playing video or sound in real time as it is downloaded over the Internet

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Some Terminologies • PPP – Point-to-Point Protocol – Protocol encapsulating a connection to a TCP/IP network through a modem and a telephone line

• PPPoE – PPP over Ethernet – The transport of PPP frames over Ethernet

• ATM – Asynchronous Transfer Mode – A high bandwidth, High speed, controlled-delay fixed-size packet switching and transmission system integrating multiple data types (voice, video, and data).

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Thank You!

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