Exploration Network Chapter 5

7/30/2019 Exploration Network Chapter 5

1/28

2007 Cisco Systems, Inc. All rights reserved. Cisco Public

ITE PC v4.0

Chapter 1 1

OSI Network Layer

Network Fundamentals Chapter 5


2/28

ITE PC v4.0

Chapter 1 2 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Objectives Identify the role of the Network Layer, as it describes

communication from one end device to another end device

Examine the most common Network Layer protocol, InternetProtocol (IP), and its features for providing connectionless andbest-effort service

Understand the principles used to guide the division or groupingof devices into networks

Understand the hierarchical addressing of devices and how thisallows communication between networks

Understand the fundamentals of routes, next hop addresses andpacket forwarding to a destination network


3/28

ITE PC v4.0


Network Layer Protocols and Internet Protocol(IP) The Network layer, or OSI Layer 3, provides services to

exchange the individual pieces of data over the networkbetween identified end devices. To accomplish thisend-to-end transport, Layer 3 uses four basicprocesses:

Addressing

Encapsulation

Routing

Decapsulation


4/28

ITE PC v4.0


Network Layer Protocols

Protocols implemented at the Network layer that carryuser data include:

Internet Protocol version 4 (IPv4)

Internet Protocol version 6 (IPv6)

Novell Internetwork Packet Exchange (IPX)

AppleTalk

Connectionless Network Service (CLNS/DECNet)


5/28

ITE PC v4.0


Network Layer Protocols and Internet Protocol(IP) Identify the basic characteristics and the role of the

IPv4 protocol


6/28

ITE PC v4.0


Network Layer Protocols and Internet Protocol(IP) Describe the implications for the use of the IP protocol

as it is connectionless


7/28ITE PC v4.0


Best Effort Service (unreliable)

Unreliable means simply that IP does not have thecapability to manage, and recover from, undelivered orcorrupt packets.

The header of an IP packet does not include fields

required for reliable data delivery. There are noacknowledgments of packet delivery. There is no errorcontrol for data. Nor is there any form of packettracking; therefore, there is no possibility for packetretransmissions.


8/28ITE PC v4.0


Media Independent

IPv4 and IPv6 operate independently of the media, any individualIP packet can be communicated electrically over cable, as optical

signals over fiber, or wirelessly as radio signals.

It is the responsibility of the OSI Data Link layer to take an IPpacket and prepare it for transmission over the communications

medium.

One major characteristic of the media that the Network layerconsiders: the maximum size of PDU that each medium cantransport. This characteristic is referred to as the MaximumTransmission Unit (MTU).

Fragmentation: Splitting a packet

to forwarding it from one media

to a media with a smaller MTU


9/28ITE PC v4.0


Packaging the Transport Layer PDU

IPv4 encapsulates, or packages, the Transport layer segment ordatagram so that the network can deliver it to the destination host.


10/28ITE PC v4.0


IPv4 Packet Header


11/28ITE PC v4.0


Conti IP Destination Address

IP Source Address

Time-to-Live

Protocol (ICMP, TCP, UDP) Type-of-Service (use for QoS e.g voice, video data etc)

Fragment Offset

Identifies the order in which to place the packetfragment in the reconstruction.

Flag

1) More Fragments flag

2) Don't Fragment flag


12/28ITE PC v4.0


Separating Hosts into Common groups

Dividing Networks

Geographic locationPurposeOwnership


13/28

ITE PC v4.0


Common issues with large networks

Performance degradation

Security issues

Address Management


14/28

ITE PC v4.0


Why separate Hosts into Networks

Improving Performance


15/28

ITE PC v4.0


Grouping Devices into Networks andHierarchical Addressing

Improving Security


16/28

ITE PC v4.0


Gateway

The gateway, also known as the default gateway, isneeded to send a packet out of the local network. If thenetwork portion of the destination address of the packetis different from the network of the originating host, thepacket has to be routed outside the original network.


17/28

ITE PC v4.0


Fundamentals of Routes, Next Hop Addressesand Packet Forwarding

Role of Gateway is to send packets to different networkwhen the destination is unknown. Router play the roleof Gateway but its interface must be on the sameNetwork/Subnet where source exist.


18/28

ITE PC v4.0


Next Hop Address

The next address/router interface to which the packetwill be route.


19/28

ITE PC v4.0


Routing Table

The routing table stores information about connected and remotenetworks.

Routes in a routing table have three main features:

Destination network

Next-hopMetric

To display routing table use

show ip route

Command.


20/28

ITE PC v4.0


Host Routing Table

A host creates the routes used to forward the packets it originates.These routes are derived from the connected network and theconfiguration of the default gateway.

The routing table of a computer host can be examined at thecommand line by issuing the netstat -r, route, or route PRINTcommands.


21/28

ITE PC v4.0



Define a route and its three key parts


22/28

ITE PC v4.0



Describe the purpose and use of the destinationnetwork in a route


23/28

ITE PC v4.0



Describe the purpose and use of the next hop in a route


24/28

ITE PC v4.0



Trace the steps of several IP packets as they arerouted through several gateways from devices on onesub network to devices on other sub networks


25/28

ITE PC v4.0



Describe the purpose of routing protocols and the needfor both static and dynamic routes


26/28

ITE PC v4.0



Explain how routes are manually configured to buildrouting table


27/28

ITE PC v4.0


Summary


28/28

Documents

Exploration Network Chapter 5