local area & ip networking

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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001

Local Area & IP Networking

Review of Week #1

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Course Overview

Network Fundamentals (w1)Medium Access Control (w2-3)Local Area Networking (w4)Routing Protocols (w5)Transport Protocols (w6)Examples/Review (w7) TEST 1IP Networking Support Protocols (w8)IP Design (w9-10) Group PresentationsApplication Support Protocols (w11-12)Network Security (w13)Makeup Week (w14) TEST 2Final Project Due last week of class

LANWAN425

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Required Reading

Computer Communications & Networking Technologies

pp. 229-274

RFC 1180 “A TCP/IP Tutorial”

Sections 1-5

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Lecture OutlineIEEE Standard LAN:

IEEE Standard LAN vs. OSI Model• LLC• MAC

Ethernet – 802.3• Overview• Frame Format

Other LAN Protocols:FDDI – ANSI X.3 (X3T9.5)

• Operation• Frame format

MAC Addressing

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Lecture Outline

IP Addressing:The IP Address

Subnetting (Classful, VLSM, CIDR)

Supernetting (CIDR)

Private vs. Public Addresses

• Address Resolution Protocol:ARP

Binding

RARP

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IP Addressing

The IP Address

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IP Addressing Scheme

A host is assigned a unique address for each network connection. The IP address is divided into a network ID and host ID. The host ID indicates the host’s connection to the network.

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IP Addressing Scheme (Cont..)

The IP address is represented by 32 bits. It is often convenient to represent the address in decimal-dot notation as shown below:

Decimal-dot : 111.23.129.8

Binary: 1101111.0010111.10000001.00001000

The Min value of an Octet (8bits) is 0, Max is 255 Network Ids assigned globally, host Ids assigned locally

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Dotted Decimal Notation

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IP AddressingThree Primary Classes

Class A : N.H.H.H Class B : N.N.H.H Class C : N.N.N.H

N = Network number assigned globally

H = Assigned by network administrator (host & subnets)

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Internet Classes

Class Range of VaulesA 0 through 126B 128 through 191C 192 through 223D 224 through 239E 240 through 255

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Internet Classes (Cont..)

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Internet Classes (Cont..)

Class A, B and C are primary classes Class D is used for multicast

- Internet hosts join a multicast group

- Packets are delivered to all members of group

- Routers manage delivery of single packet from source to all members of multicast group

- Used for mbone (multicast backbone) Class E is reserved

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Computing The Class Of An Address

First four bits Index Class 0000 0 A 0001 1 A 0010 2 A 0011 3 A 0100 4 A 0101 5 A 0110 6 A 0111 7 A 1000 8 B 1001 9 B 1010 10 B 1011 11 B 1100 12 C 1101 13 C 1110 14 D 1111 15 E

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Class Ranges Of Internet Addresses

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IP Addressing - Class A (example)

1.222.222.222 Network # : 1 Host # : 222.222.222

Range of network numbers is : 1-126 (0 and 127 reserved) Maximum number of class A networks : 126 Number of available hosts : 16,777,214 (all 0’s and all 1’s

reserved)

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IP Addressing - Class B (example)

128.128.222.222 Network # : 128.128 Host # : 222.222

Range of network numbers is : 128 - 191 Maximum number of networks : 16384 Number of available hosts : 65,534

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IP Addressing - Class C (example)

192.192.192.222 Network # : 192.192.192 Host # : 222

Range :192- 223 Maximum number of networks : 2097152 Number of available hosts : 264 per network

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IP First Octet Rule

1 - 126 : Class A 128 - 191 : Class B 192 - 223 : Class C

224 - 239 : Class D 240 - 254 : Class E

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Summary of Special IP Addresses

Prefix Suffix Type Purposeall 0s all 0s this computer used during bootstrap

network all 0s network identifies a network

network all 1s directed broadcast broadcasts on a specified net

all 1s all 1s limited broadcast broadcast on a local net

127 any loopback testing

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IP Addressing Example

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Reference Information

IP Address Class

Format Purpose High-Order Bit(s)

Address Range # of Bits Network/

Host

Max. Host

A N.H.H.H Large organizations

0 1.0.0.0 to 126.0.0.0

7/24 16,777,2142 (224-2)

B N.N.H.H Medium organizations

1,0 128.1.0.0 to 191.254.0.0

14/16 65,534 (216-2)

C N.N.N.H Small organizations

1,1,0 192.0.1.0 to

223.255.254.0

22/8 254 (28-2)

D N/A Multicast groups

1,1,1,0 224.0.0.0 to 239.255.255.255

N/A N/A

E N/A Experimental 1,1,1,1 240.0.0.0 to 254.255.255.255

N/A N/A

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CLASSFUL & SUBNET MASKING

PART 1

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CLASSFUL & SUBNET MASKING

• Classic natural mask addresses– Difficult to manage devices on each network

– A Class B address, for example, must manage large numbers of devices

• Subnetting– Simplified the address management process

– Better address optimization

• Original classful addressing– Did not anticipate Internet growth

– Originally allocated based on organization, not need

• Classful A, B, and C addressing– A concept that is easy to understand

– Still wasteful

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THE CONCEPT OF MASKING

A Class B address:

184 . 10 . 0 . 01011 1000 . 0000 1010 . 0000 0000 . 0000 0000

NetID HostID

1111 1111 . 1111 1111 . 0000 0000 . 0000 0000 255 . 255 . 0 . 0

The Mask:

Or:

In other words, we can write this as:

184.10.0.0/16

184 . 10 . 0 . 0 / 16

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1101 0000 . 1000 1000 . 0011 1010 . 0000 0000

1011 0111 . 1111 0000 . 0000 0000 . 0000 0000

CLASSFUL ADDRESSES

A Class B classful address:

183.248.0.0/16

A Class C classful address:

208.136.58.0/24

A Class A classful address:

0001 1100 . 0000 0000 . 0000 0000 . 0000 0000

28.0.0.0/8

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JUST A NOTE

Also written:

127/8

Or:

127.0.0.0/8

The Class A address:

127.0.0.0

Has been reserved for “Loopback” interface where a client and server are allowed to communicate with one another when they are located on the same host.

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HOW MANY NETWORKS/HOSTS ARE ALLOWED?

• Class B address ID allows for 214 - 2 networks, or 16,382

– Because first 2-bits define a Class B address, and

– All Os (set aside for an initialization process) and all 1s (set aside for

broadcast)

• Class B host ID allows for 216 - 2 hosts, or 65,534

– Because all 0s are set aside for meaning “this network” and

– All 1s are set aside for broadcasting to all hosts on this network

• This applies to Class A and Class C addresses as well

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SUBNETTING CLASSFUL ADDRESSES

• You are given a Class B address 141.6.0.0/16• This will give you 216 - 2 hosts or 65,534 devices on this network• Subnetting this classful address potentially makes this more manageable

NOTE: Subnetting steals from the HOSTs to give to the Network ID

/ 18

/ 24

/ 28

4 subnets & 16,382 hosts

256 subnets & 254 hosts


141 . 6 . 0 . 0

141 . 6 . 0 . 0

141 . 6 . 0 . 0

141 . 6 . 0 . 0

1000 1101 . 0000 0110 . 0000 0000 . 0000 0000

1000 1101 . 0000 0110 . 0000 0000 . 0000 0000

1000 1101 . 0000 0110 . 0000 0000 . 0000 0000

1000 1101 . 0000 0110 . 0000 0000 . 0000 0000

/ 16

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SUBNETTING CLASSFUL ADDRESSES

• Let us focus on the classful address 141.6.0.0/28

/ 28141 . 6 . 0 . 0

1000 1101 . 0000 0110 . 0000 0000 . 0000 0000

• 212 = 4096 subnets are possible but– All 0s and all 1s are potentially not allowed - RFC 950– Function of the Interior Gateway Protocol (IGP) in use– Today, all 0 and all 1subnet addresses ARE available

• 24 = 16 hosts are possible, but– All 0s and all 1s are still not allowed– Or 24 - 2 = 30 hosts on each subnetwork

• Therefore– 4096 subnests and– 30 hosts on each subnet

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AN EXAMPLE

• You are given the Class C address of


198 . 6 . 1 . 0 / 29

1100 0000 . 0000 0110 . 0000 0001 . 0000 0000

• Defining Subnet Numbers

Subnet O (000002)

Subnet 1 (000012)

• Thus, the address of Host 5 on Subnet 30 is 188.6.1.21 or

1100 0000 . 0000 0110 . 0000 0001 . 1111 0101

Subnet 31 (111112)

Subnet 30 (111102)

•••

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198 . 6 . 1 . 0 255 . 255 . 255 . 236

A 2nd EXAMPLE OF MASKING USING LOGICAL ‘AND’

• You are given the Class C address and mask of

32 subnets & 6 hosts1100 0110 . 0000 0110 . 0000 0001 . 0000 0000

• Defining Subnet and Host Numbers

• Thus, the address of Subnet 30 & Host 5 is 188.6.1.250 or

1100 0110 . 0000 0110 . 0000 0001 . 1111 1010

Subnet O (000x00xx2)

Subnet 1 (000x01xx2)



•••

1111 1111 . 1111 1111 . 1111 1111 . 1110 1100

Host 5 (xxx1xx102)

Host 4 (xxx1xx012)

•••

Host O (xxx0xx012)

Host 1 (xxx0xx102)

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TERMINOLOGIES

• You are given the Class B address of

1000 0010 . 0110 0101 . 0000 0000 . 0000 0000

130 . 101 . 0 . 0 / 24

1000 0010 . 0110 0101 . 0000 0000 . 0000 0000

• Masking terms– Natural mask also called the network-prefix

– Subnet mask

1000 0010 . 0110 0101 . 0000 0000 . 0000 0000

– Extended-network-prefix = natural plus subnet masks

1000 0010 . 0110 0101 . 0000 0000 . 0000 0000

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VARIABLE LENGTH SUBNET MASKS (VLSMs)

PART 2

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VARIABLE LENGTH SUBNET MASK (VLSM)

• With subnet masking, one network, one mask

• With VLSM, one network can be configured with different masks

• Example: You are assigned a Class C address of 196.4.1.0/24. You need to divide that network into 3 subnets

196.4.1.0/24 255.255.255.X

– Example: You are assigned a Class C address of 190.4.1.0/24. You need to divide that network into 3 subnets

– Subnet masking choices given X :

– Subnet 1 needs to host 100 devices

– Subnet 2 needs to host 50 devices, and

– Subnet 3 needs to host 50 devices.

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VLSM EXAMPLE

196.4.1.0/24255.255.255.X


X = 252 (1111 1100) - 64 subnets with 2 hosts each






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VLSM EXAMPLE - CONT’D

196.4.1.0/24255.255.255.X




Subnet 1 - 126 hosts

Subnet 2 - 126 hosts

Subnet 1 - 62 hosts

Subnet 2 - 62 hosts

Subnet 3 - 62 hosts

Subnet 4 - 62 hosts

Router

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196.4.1.0/26E4 1100 0100 . 0000 0100 . 0000 0001 . 11xx xxxx

196.4.1.0/26E3 1100 0100 . 0000 0100 . 0000 0001 . 10xx xxxx

196.4.1.0/25E1 1100 0100 . 0000 0100 . 0000 0001 . 0xxx xxxx

196.4.1.0/24E0 1100 0100 . 0000 0100 . 0000 0001 . xxxx xxxx


• The VLSM solution :

196.4.1.0/25E2 1100 0100 . 0000 0100 . 0000 0001 . 1xxx xxxx

E1 126 hosts

E4 62 hostsE3 62 hosts

E1 126 hosts

E3 126 hosts

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196.4.1.0/27E5 1100 0100 . 0000 0100 . 0000 0001 . 110x xxxx

196.4.1.0/27E6 1100 0100 . 0000 0100 . 0000 0001 . 111x xxxx

196.4.1.0/26E4 1100 0100 . 0000 0100 . 0000 0001 . 11xx xxxx

196.4.1.0/26E3 1100 0100 . 0000 0100 . 0000 0001 . 10xx xxxx

196.4.1.0/24E0 1100 0100 . 0000 0100 . 0000 0001 . xxxx xxxx


• More splitting :

E1 126 hosts

E3 62 hosts


E0254 hosts

196.4.1.0/25E1 1100 0100 . 0000 0100 . 0000 0001 . 0xxx xxxx

196.4.1.0/25E2 1100 0100 . 0000 0100 . 0000 0001 . 1xxx xxxx

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ANOTHER VIEW OF VLSM

E1126 hosts

E362 hosts

E630 hosts

E530 hosts

E2126 hosts

E462 hosts

E0254 hosts

E1 126 hosts

E3 62 hosts


E0254 hosts

Ethernet Hub

VLSM Cascaded Routers

Single VLSM Router

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AGGRIGATION & ADVERTIZMENTS

A real advantage. Here’s why:

Network-Prefix Host-Number

Two-Level Classful Hierarchy

SubnetNumber

HostNumber

Network-Prefix

Three-Level Classful Hierarchy

E1 141.6.32.0E2 141.6.64.0E3 141.6.96.0E4 141.6.128.0E5 141.6.160.0E6 141.6.192.0E7 141.6.224.0

IPNetwork

E0 141.6.0.0/ 24

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Autonomous Network

VLSM PERMITS ROUTE TABLE AGGRIGATION & ADVERTIZEMENT

11.1.1.0/2411.1.2.0/24

•••

11.1.253.0/2411.1.254.0/24

11.1.253.32/2711.1.253.64/27

••

11.1.253.160/2711.1.253.192/27

11.1.0.0/1611.2.0.0/1611.3.0.0/16

••

11.252.0.0/1611.253.0.0/1611.254.0.0/16

11.253.32.0/1911.253.64.0/19

••

11.253.160.0/1911.253.192.0/19

IPNetwork

11.1.0.0/16

B

D

11.1.253.0/2711.253.0.0/19

CNOTE: It may help to write these numbers in dot binary and use a marker to define the appropriate mask

11.0.0.0/8or 11/8 A

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VLSM PERMITS ROUTE TABLE AGGRIGATION & ADVERTIZEMENT (con’d)

Autonomous Network

11.1.1.0/2411.1.2.0/24

•••

11.1.253.0/2411.1.254.0/24

11.1.253.32/2711.1.253.64/27

••

11.1.253.160/2711.1.253.192/27

11.1.0.0/1611.2.0.0/1611.3.0.0/16

••

11.252.0.0/1611.253.0.0/1611.254.0.0/16

11.253.32.0/1911.253.64.0/19

••

11.253.160.0/1911.253.192.0/19

11.1.0.0/16

B

D

11.1.253.0/2711.253.0.0/19

C

000 1011.0000 0001.1111 1101.0010 0000 32000 1011.0000 0001.1111 1101.0100 0000 64000 1011.0000 0001.1111 1101.0110 0000 96000 1011.0000 0001.1111 1101.1000 0000 128000 1011.0000 0001.1111 1101.1010 0000 160000 1011.0000 0001.1111 1101.1100 0000 192

27

000 1011.1111 1101. 0010 0000 32000 1011.1111 1101. 0100 0000 64000 1011.1111 1101. 0110 0000 96000 1011.1111 1101. 1000 0000 128000 1011.1111 1101. 1010 0000 160000 1011.1111 1101. 1100 0000 192

19

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SUMMING UP SUBNETS & VLSM SO FAR

• Classic natural mask addresses– Difficult to use

– Very address wasteful

• Subnetting– Simplified the address management process

– Better address optimization

• VLSM– Also simplifies address management

– Also improves address optimization over subnetworking

– Simplifies routing tables

– Simplifies address advertising

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SUMMING UP SUBNETS & VLSM SO FAR

• Not all routing protocols can handle VLSM. Early network protocols did not– Routing Information Protocol (RIP) Version 1

– Interior Gateway Routing Protocol (IGRP) which is Cisco proprietary

• Today’s routing protocols do support VLSM– Open Shortest Path First (OSPF)

– Enhanced Internet Gateway Protocol (EIGRP), a Cisco proprietary protocol

– Intermediate System-to-Intermediate System (IS-IS)

– RIP Version 2

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Private vs. Public Addresses• Some IP Addresses have been reserved for private

use meaning that they cannot be routed over the Internet. Specifically, the following networks are reserved for private use.

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Private IP AddressesPrivate addresses can only be used for internal

networks. RFC 1918 spells out a set of addresses which are prohibited from being used on the Internet.

Network Address Available Allocation10.0.0.0 1 Class A network

172.16.0.0 through 172.31.0.0 16 Class B networks

192.168.255.0 through 192.168.255.0 255 Class C networks

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ARP - Binding

The interface between IP Addresses and MAC Addresses

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What Is Binding ?

Association between a protocol address and a hardware(MAC) address is called a binding

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What Is Address Resolution ?

Translation from a computer’s protocol address to an equivalent hardware address

or

Mapping between a protocol address and a hardware address

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Why Address Resolution ?

Upper levels of protocol stack use protocol addresses (example = IP addresses)

Network hardware must use hardware address for eventual delivery (example = MAC addresses)

Protocol address must be translated into hardware address for delivery (LAN Equipment, at layer 2, will bind MAC addresses to IP Addresses)

Translation occurs in data link layer

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A computer never resolves the MAC address of a computer attached to a remote network

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Address Resolution

How can Node A resolve the MAC address of Node B?How can it resolve the MAC address of Node F?How can it resolve the MAC address of Router R1?

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Address Resolution Techniques

Three techniques : Table lookup Closed-form computation Message exchange (dynamic)

TCP/IP can use any of the three methods

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Table Lookup

IP Address Hardware Address

197.15.3.2 0A:07:4B:12:82:36197.15.3.3 0A:9C:28:71:32:8D197.15.3.4 0A:11:C3:68:01:99197.15.3.5 0A:74:59:32:CC:1F197.15.3.6 0A:04:BC:00:03:28197.15.3.7 0A:77:81:0E:52:FA

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Table Lookup (Cont.......)

A0:14:52:44:F2:910A:07:4B:12:82:360A:9C:28:71:32:8D0A:11:C3:68:01:990A:74:59:32:CC:1F0A:04:BC:00:03:28

197.15.3 .5

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Closed-form Computation Network administrator can choose hardware address based

on IP address Example - hardware uses one octet address that can be

configured Simply choose hardware address to be hostid

hardware_address = ip_address & 0xff

THIS IS TECHNIQUE IS NOT ADVISED!!!!!

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Message Exchange (Dynamic Resolution)

S erver b ased D is trib u ted

M essag e exch an g e

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Message Exchange(Dynamic Resolution) (Cont.)

Use network to resolve IP addresses Message exchange with other computer(s) returns hardware address to source Server based :- computer sends message to server to

resolve address

Distributed (ARP):- all computers participate; destination

provides hardware address to host

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Distributed Dynamic Resolution Or Address Resolution Protocol

(ARP)

TCP/IP uses distributed resolution technique Address Resolution Protocol (ARP) - part of TCP/IP

protocol suite Two-part protocol

Request from source asking for hardware address Reply from destination carrying hardware address

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Distributed Dynamic Resolution Or Address Resolution Protocol (ARP)

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Distributed Dynamic Resolution Or Address Resolution protocol

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ARP Message Format

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ARP Message Format (Cont........)

HARDWARE ADDRESS TYPES= 1 for Ethernet PROTOCOL ADDRESS TYPES = 0x0800 for IP HADDR LEN & PADDR LEN (number of octets in

hardware & protocol address) OPERATION = 1 (for request);

= 2 (for response)

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Reverse ARP (RARP)

What is the IP address of a given hardware address ? Hardware to IP address resolution Used by diskless systems to find their own IP address

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RARP Illustrated

Ethernet : 0800.0020.1111IP = ????

IP = 131.108.3.1

I know who you are, here’s your IP

address

Here’s my MACaddress. What is my

IP address ?

131.108.3.20800.0020.1111

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IP Addressing Protocols

RARP

BOOTP

ICMP

DHCP

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Bootstrapping• Computer loads a simple boot program. The boot program

loads operating system

• When is protocol software loaded during booting?

• Protocol software may be:

- Run out of on-board PROM

- Loaded with bootstrap program from disk

- Loaded with operating system from disk

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Diskless Machines• Uses network as part of the bootstrap process

• The computer needs to know the network address of the o/s file

• It needs to know its own IP address

• It only knows its h/w address

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Configuration

• Protocols are software routines

• Protocol software employs parameters for operation on a specific hardware and network

• Different nodes have different parameters

“Configuration = setting the parameters”

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Example Parameters• IP address - depends on network, must be unique on

network

• Default router address - where to send packets aimed at remote network

• Subnet mask - to specify if subnet addressing is used and what the subnet is

• DNS server address - for DNS queries

• Server addresses

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Methods Of Protocol Configuration

Manual Loca l d isk file

R AR P IC MP BO O TP D H C P

Autom ated through network

Methods

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Automated Protocol Configuration

• How can host use network to get network address? • Use broadcast-based link-layer protocol

- RARP

- AppleTalk, etc.

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RARP

• Reverse ARP (remember): “What is the IP address of hardware address xx:xx:…..?”

• Host broadcasts RARP request with its MAC address

• But RARP uses IP => Needs IP address

• Solution: Use 00.00.00.00 as source address

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ICMP

• ICMP address mask request - find subnet mask

• ICMP gateway discovery - find default router

• Host broadcasts ICMP queries

• Problem: What is the bootfile name for IP address nn.nn.nn…?

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Sequence Of Protocols Used During Bootstrap

1. Broadcast RARP request

2. Extract IP address from RARP response

3. Broadcast ICMP address mask request

4. Extract subnet mask from ICMP address mask

reply

5. Broadcast ICMP gateway discovery request

6. Extract default router from ICMP gateway

discovery reply

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BOOTP• Allows remote booting from a server on the same network

or different physical network

• Broadcast BOOTP (Bootstrap protocol) request

• Reply: IP address, Boot Server IP address, Default router, Bootfile name, subnet mask

• Host gets boot image using a simple FTP program

- Trivial File Transfer Protocol (TFTP)

• Problem: Why waste an address when it is not being used

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BOOTP Message Format

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DHCPDynamic Host Configuration Protocol (DHCP), was

devised by the IETF to automate configuration of terminal IP addresses.– DHCP provides a mechanism that allows a computer to

join a new network an d obtain an IP address without manual intervention.

– Terminals use client software to send a DHCP Request when booted.

– A terminal running DHCP software will send a DHCP Reply containing an IP address and a default gateway to the terminal.

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DHCPIP addresses are leased for a finite period of time.

When a lease ends, the terminal must request another IP address or an extension to the lease.– Terminals must discover if a DHCP server exists

through a DHCP Discover message. The terminal will cach the server location for future use.

– DHCP message carry no information about DNS servers!

What happens to servers using DHCP that have entries in a DNS database?

local area & ip networking

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