Tài liệu giảng dạy CCNA - module 01 chapter 05 - Fundamentals of IP

IP address classes To accommodate different size networks and aid in classifying these networks, IP addresses are divided into groups called classes..  To create a subnet address, a ne

Module 01 InterNetwork Overview

Chapter 05 Fundamentals of IP

1 Typical Features of OSI Layer 3

Routing overview

 Routing is an OSI Layer 3 function.

 Routing is the process of finding the most efficient path from one

device to another

 The primary device that performs the routing process is the router.

other routers know of changes in the network

topology.

interface, adds the necessary framing information for the interface, and then transmits the frame

Routing Logic: PC1 Sending to PC2

Token Ring

Destination Is

in another Group; Send

to Nearby Router. to that Group Is My Route

Out Serial Link.

My Route

to that Group Is Out Frame Relay.

Send Directly

to PC2

Network Layer and Data Link Layer

Encapsulation

Frame-Relay

Token Ring

Extract IP Packet and Encapsulate in HDLC

Extract IP Packet, and Encapsulate in Frame Relay

Extract IP Packet, and Encapsulate in Token Ring

TR IP Packet

Eth IP packet

HDLC IP packet

FR IP packet

Routing Protocol

• Routing protocols allow routers to choose the best

path for data from source to destination.

• Functions includes the following:

– Provides processes for sharing route information.

– Allows routers to communicate with other routers

to update and maintain the routing tables

IP Routing and Routing Protocols

Frame-Relay 150.150.3.0

Token Ring

Default router: 150.150.1.4

2 IP Addressing Fundamentals

IP address classes

 To accommodate different size networks and aid in classifying these networks, IP addresses are divided into groups called classes This

is known as classful addressing

Class A Network Host

IP address classes: Class A

IP address classes: Class A

 The first bit of a Class A address is always 0

 The first 8 bits to identify the network part of the address

 Possible network address from 1.0.0.0 to

126.0.0.0

 The remaining three octets can be used for the

host portion of the address

 Each class A network have up to 16,777,214

possible IP addresses( 224-2)

IP address classes: Class B

IP address classes: Class B

 The first 2 bits of a Class B address is always 10

 The first two octets to identify the network part of the address

 Possible network address from 128.0.0.0 to

191.255.0.0 (2 14)

 The remaining two octets can be used for the

host portion of the address

 Class B network have up to 65.534 possible IP

addresses (2 16 -2)

IP address classes: Class C

IP address classes: Class C

 The first 3 bits of a Class C address is always 110

 The first three octets to identify the network part

How IP Addresses Are Grouped

Why we need to divide network?

 Network administrators sometimes need to divide

networks, especially large ones, into smaller networks:

 Reduce the size of a broadcast domain.

 Improve network security.

 Implement the hierarchical managements.

 So we need more network addresses for your network

But I want the outside networks see our network as a

single network.

Without subnet

131.3.0.0

Divide network by three

131.108.3.0

•The NIC can assign one or a few network numbers to an

organization, and then the organization can subdivide

those networks into subnets of more usable sizes.

 To create a subnet address, a network administrator

“ borrows” bits from the original host portion and

designates them as the subnet field

 “Borrows” bits is always the leftmost host bit, the

one closest to the last network octet.

 Subnet addresses include the Class A, Class B, or

Class C network portion, plus a subnet field and a

host field.

 Subnet addresses are assigned locally, usually by a

network administrator.

Establishing the subnet mask

address

 “Extended Network Prefix”

 Give router the information to determines

which part of an IP address is the network field

and which part is the host field

 32 bits long, divided into four octets

 Network and Subnet portions all 1’s

 Host portions all 0’s

Subnet mask: Example

Class C Network address: 192.168.10.100/255.255.255.0 (or /24)

3 Network Layer Utilities

Address Resolution Protocol (ARP)

 In order for devices to communicate, the

sending devices need both the IP addresses and the MAC addresses of the destination devices

 When they try to communicate with devices

whose IP addresses they know, they must

determine the MAC addresses

 ARP enables a computer to find the MAC address

of the computer that is associated with an IP

address

Address resolution protocol

ARP table in host

RA M

RA M

197.15.22.33 IP

197.15.22.126 Data

ARP: Destination local

35

 The DNS server is a device on a network that

manages domain names and responds to

requests from clients to translate a domain

name into the associated IP address

 The DNS system is set up in a hierarchy that

creates different levels of DNS servers

.

DNS: Database

.

vn com

www – 203.162.50.100

www – 203.162.50.100

ctt – 203.162.50.1 aaa – 203.162.70.201 bbb – 203.160.9.7

ctt – 203.162.50.1

aaa – 203.162.70.201 bbb – 203.160.9.7

Address

of com server

Address

of com

server

Address of yahoo.com server

Address of

yahoo.com

server

Address of www.yahoo.com

ICMP Echo and the ping Command

Is B reachable

Yes, I am here.

B

ICMP echo reply ICMP echo request

 Reverse address resolution protocol (RARP) binds MAC

addresses to IP addresses.

its IP address in diskless workstations or dumb

terminals Devices using RARP require that a RARP

server

and an ARP request message.

direct them to start the RARP process, and locate the

RARP server.

IP of server Filename of boot file

IP Address Gateway

IP of server Filename of boot file

• A device uses BOOTstrap protocol (BOOTP)

when it starts up, to obtain an IP address BOOTP uses UDP to carry messages; the UDP message

is encapsulated in an IP datagram

• A computers uses BOOTP to send a broadcast

IP datagram (using a destination IP address of all 1s - 255.255.255.255), a BOOTP server receives

the broadcast and then sends a broadcast

• The client receives a datagram and checks the

MAC address, if it finds its own MAC address in

DHCP

a successor to BOOTP Unlike BOOTP, DHCP allows a host to

obtain an IP address quickly and dynamically.

 All that is required using DHCP is a defined range of IP addresses

on a DHCP server (commonly referred to as a scope)

 As hosts come online they contact the DHCP server and request

an address The DHCP server chooses an address and allocates it

to that host

DHCP Offer UDP Broadcast

DHCP server

IP1 IP2

Gateway

Gateway

IP of other servers

IP Address Lease time DHCP sever IP Address

IP Address Lease time DHCP sever IP Address