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TCOM 509 – Internet Protocols (TCP/IP)

Lecture 02_b

Instructor: Dr. Li-Chuan ChenDate: 09/08/2003

Based in part upon slides of Prof. J. Kurose (U Mass), Prof. B. Yener (Rensselaer Polytechnic Institute)

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Outline

Chapter 4 – Classful Internet Address Chapter 5 Chapter 6 Chapter 7

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Flat vs. Hierarchical Addresses Flat addresses

• no structure in them to facilitate scalable routing.• e.g., Ethernet addresses

Hierarchical addresses• Network part (netid) and host part (hostid).• Helps identify direct or indirectly connected nodes.• Efficient for routers to send packets.

netid hostid

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Internet Addresses

Classful Internet Address• Class A• Class B• Class C• Class D• Class E

Goal: Allows any computer to communicate with any other computer in a global communication network.

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IP Address Formats

Class A netid hostid071 24 bits

netid hostid10142 16 bits

Class B:

netid hostid110213 8 bits

Class C:

Multicast Group addresses1110284 bits

Class D:

Class E: Reserved for future uses1111284 bits

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IP Addresses IP Address

• 32-bit global internet address• Network part (netid) and host part (hostid)• Class D addresses are for multicasting (packet is

delivered to a subset of hosts).• Unicast: a packet is delivered to a single host.• Reserved addresses

– All 0 (binary 0000000) is reserved– All 1s broadcast address (limited broadcast) can be used in

start-up to get its IP address. – Loopback 127.x.x.x– hostid 0 refers to the network itself, not individual host.– hostid consist of all 1s is for directed broadcast to all hosts on

the network.

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IP Addresses – Class A Class A – small networks with large number of

hosts.• Starts with binary 0, followed by 7-bit Network field, and

then 24-bit Host field• netid of 127 (binary 01111111) is reserved for loopback• Only 2 7 – 2 = 126 octets left, range 1.x.x.x to 126.x.x.x• Covers 50% (231) of the entire IP address space• 224 for each Class A network. Millions of Class A

addresses are wasted

netid hostid071 24 bits

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IP Addresses - Class B

Class B – intermediate size networks.• Starts with 10, followed by 14-bit Network field, and

then 16-bit Host field• Range 128.x.x.x to 191.x.x.x• 214 = 16,384 class B addresses• Covers 25% (230) of the entire IP address space• 216 for each Class A network. Many of Class B

addresses are wasted

netid hostid10142 16 bits

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IP Addresses - Class C Class C – large networks with small number of

hosts.• Starts with 110, followed by 21-bit Network field, and

then 8-bit Host field• Range 192.x.x.x to 223.x.x.x• 221 = 2,097,152 networks, 28 = 256 hosts in each

network• Covers 12.5% (229) of the entire IP address space

netid hostid110213 8 bits

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IP Addresses - Class D, E Class D – Multicasting

• Starts with 1110, followed by 28-bit multicast group address.• 228 multicast groups• Covers 6.25% (228) of the entire IP address space

Multicast Group addresses1110284 bits

Class E – Reserved• Starts with 1111, followed by 28-bit multicast group address.• Covers 6.25% (228) of the entire IP address space

Reserved for future uses1111284 bits

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Dotted Decimal Notation IP address (32 bits) can be written as four

decimal integers separated by decimal points.

IP address is divided into 4 parts, convert each part from binary to its equivalent decimal integer.

Example Binary: 10000000 000001010 00000010 00011110

Dotted Decimal: 128.10.2.30

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IP Addressing IP address: 32-bit identifier for

host, router interface Interface: connection between

host, router and physical link• router’s typically have

multiple interfaces • host may have multiple

interfaces• IP addresses associated

with interface, not host, router

Hosts in the same network have same network ID

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

223.1.1.1 = 11011111 00000001 00000001 00000001

223 1 11

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IP Address

Class Range

A 0 - 127

B 128 - 191

C 192 - 223

D 224 - 239

E 240 - 255

Lowest Address

Highest Address

1.0.0.0 126.0.0.0

128.1.0.0 191.255.0.0

192.0.1.0 223.255.255.0

224.0.0.0 239.255.255.255

240.0.0.0 255.255.255.254

Some values are reserved.

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Reserved Addresses Loopback: test for inter-process communication

on the local host. Hostid “this” (0s), “all” (1s)

All 0s Host

Network All 1s

All 0s

All 1s

127 anything

This host

Host on this network

Limited broadcast

Directed broadcast

Loopback

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IP Addresses - ConsIP Address Cons: IP address is associated with network connection, not to

the host. Difficult and time consuming to change network

addresses. e.g., when class C network grows to > 255 (28) hosts.

If a host has multiple addresses (multi-homed host), knowing one address may not be sufficient to reach it when this particular path to that address is down.

Nearly all allocated• Need next-generation IP protocol - IPv6

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Subnet and Supernet Extensions Classful addressing inefficient: Everyone wants

class B addresses Can we split class A, B addresses spaces and

accommodate more networks ?• Need another level of hierarchy. Defined by subnet

mask, specifies the sets of bits belonging to the network address and host address respectively .

Supernetting or classless addressing allows prefix and suffix to occur at an arbitrary point.

Network Host

Boundary is flexible, will cover in details later

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Network Byte Order Use standard byte ordering (Big Endian) within protocol

fields so all hosts interpret the IP addresses the same way.

Big Endian: integers are sent with the most significant byte first.

Little Endian: integers are sent with the least significant byte first.

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Chapter 4 Summary• IP address uses 32-bit binary number.• Unique IP address per interface.• Provision for broadcast, multicast, loopback

addresses.• Classful (A,B,C) address allocation not efficient.• Hierarchical addresses are more efficient with

smaller routing tables.• Extended address scheme: subnet and supernet

addressing improved address allocation efficiency (cover later).

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Homework 1Chapters Problems

2 7

4 1, 7

Due Monday 09/15/2003