Routing Fundamentals and Subnets Introduction to IT and Communications Technology CE00378-1.

Routing Fundamentals and Subnets

Introduction to IT and Communications Technology

CE00378-1

Content Describe routed protocols List the steps of data encapsulation in an internetwork as

data is routed to Layer 3 devices Describe connectionless and connection-oriented

delivery Name the IP packet fields Describe how data is routed Compare and contrast different types of routing protocols List and describe several metrics used by routing

protocols List several uses for subnetting Determine the subnet mask for a given situation Use a subnet mask to determine the subnet ID

IP Address A packet of data can be sent to a particular

network by ANDing it with the network MaskFor a Class C Address this would be

255.255.255.0All of the bits which represent the network ID are

set to 1 the rest are set to 0When the IP address converted to binary is AND’d

with the network mask only the Network ID is displayed

This network address can then be used for routing the packet to the correct interface

IP Address Example

IP address grouping

•All of these addresses can be represented in a routing table by the network address•192.168.10.0

•Rather than the full 254 addresses which could be added

Routed protocol A routed protocol

Is one where it is used carry out addressing across the network

The most common example would be IP

Network layer devices in data flowE

ncap

sula

te Decapsulate

A IP Packet being transferred across a network with three routers

Router protocol stripping As a packet of information is transported

between two pointsThe level 1 and 2 frame information will be

stripped and replacedThis can be done due to a different technology

being connected on the next segment of the journey

It may be changing the header with the address of the next point on the route

The IP and above layers (3 to 7) will remain the same throughout the transport of the packet

Router protocol stripping Example

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Connectionless network services•In connectionless services the packets are just transferred between devices

•No communications are agreed before sending data, all of the packets may take different routes to the same destination based on local conditions•Commonly referred to as Packet switched communications

Connection orientated services•In connection orientated services, the route is worked out before communications start

•A telephone network is an example of this•Commonly referred to as Circuit Switched networks

Network layer fields

All of the field lengths are fixed except for IP Options and Padding fields

•The most common Network layer (Routed) protocol is IPv4 at the moment•Below is the layout of the protocol with the additional information which needs to be transferred with the data element

Routing metrics•The routing metrics are the values which are used to work out the best route between two points when offered more than one route

•Metrics can be•Delay•Hop Count•Bandwidth•Load•Cost•Reliability

Data encapsulation Encapsulation

Is the adding of information to the packet Decapsulation

Is the removal of this information

En

cap

sulation

Dec

apsu

latio

n

The network layer routing•The switch will allow routing in the local LAN

•A packet of information will be forwarded out of a particular interface based on the MAC address of the device attached to it

•Routers forward based on the IP address (Network layer) information

Layer 2 switching & layer 3 routing

ARP tables & routing tables

Router and switch feature comparison

Routed protocol

Routing protocol•A routing protocol is used to work out the best route based on metrics between multiple points

Routing process

Routing tables

Routing algorithms and metrics

Interior & exterior gateway protocols

Link-state & distance-vector

Distance Vector protocols Use the distance, direction and vector to any point in the network

RIP Distance Vector

IGRP Distance Vector

EIGRP Distance Vector

Link State protocols Send periodic updates to the network regarding the knowledge they

have OSPF

Link State

IP address bit patternsIP Protocols are made up two parts

NETWORK ID and Host IDDepending on the class is how many bits are represented by each part

IP Subnets IP Addresses are made up of

Network ID Host ID Depending on the class this dictates the size of each

element. The host ID part though can be split again to extend

the length of the Network ID Example would be a Class C address by default

Network ID is 24 bits and Host ID is 8 bits By borrowing bits from the host id the network ID is expanded

The disadvantage is that the number of possible hosts are reduced hosts

Subdividing the host octets of a class C address

Subdividing the host octets of a class B address

Subdividing the host octets of a class A address

Subnetting chart (bit position and value)

Subnetting chart for a class C address (subnet mask identifier)

Subnetting

Subnetting chart

Subnet scheme

Borrowing 3 bits – therefore subnetwork addresses go up in multiples of 32

Subnetting chart

•The logical ANDing process•This process is used to work out the network part of the IP address for routing purposes

Calculating the subnet ID

Summary of lecture

IP AddressingRouting of these protocols Subnets Class C

Routing Protocols Serial Interfaces for WAN’s