Chapter 4

Network LayerWith special emphasis on Internet

Protocol (IP)

Contents

• Functions of network layer• Internet protocol (IP)• IP Header• IP Addresses

• CIDR notation• Obtaining IP addresses• IP version 6

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Functions of the Network layer

• Transfer variable length data packets from a source network to a destination network via one or more networks

• This task is called Routing

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Functions of the Network layer

Router 3(R3)

Router 2(R2)

Router 1 (R1)

Web server

PC user

DL

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ion

= R

1's

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addr

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IP d

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n =

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r’s IP

ad

dres

s

IP d

ata

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dest

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ion

= R

2's

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addr

ess

IP d

estin

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n =

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eb s

erve

r’s IP

ad

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s

IP d

ata

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dest

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ion

= R

3's

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estin

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r’s IP

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IP d

ata

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dest

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ion

= W

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estin

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Routing and road trips

• Consider a long distance road trip

• The source and final destination are like network layer addresses

• Each interstate exit is like a data link layer address

IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Internet protocol (IP) overview

• Most common protocol at the Network Layer

• Specified in RFC 791 (Sep 1981)• First used on a large scale in BSD UNIX

– http://www.isoc.org/internet/history/brief.shtml– Now used by default in all operating systems

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP packet within data link frameD

ata-

Link

la

yer

Hea

der

IP Header

Data passed to IP from Transport layer

Dat

a-Li

nk

laye

r F

CS

Data from IP layer to data link

layer

IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP capabilities

• Highly adaptable– Most current uses of the Internet (http, IM, bit-

torrent, movie downloads) did not exist at the time of creation of IP

– Even email was only specified a year later in Aug 1982 in RFC 821

– But IP can serve all these applications– IP does not provide end-to-end reliability,

sequencing etc

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP Header

VersionHeader length

Type of service Total length

Identification Flags Fragment offset

Time to live Protocol Header checksum

Source address

Destination address

PaddingOptions

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Note: Each tick mark represents a bit position

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP Header fields

• Like other layers, IP header fields enable IP functionality– Used primarily by routers to find addresses

• Version

• Header length– Length of header in multiples of 32 bits – minimum value = 5

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addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP Header fields

• Type of service– Packets with higher value should get higher

priority– But generally not currently implemented

• Total length– Size of packet, including header and data

• ID– Used to re-assemble packet if it is fragmented by

intermediate routers11

IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP Header fields

• Flags– Indicates whether packet may be further

fragmented, and whether it has in fact, been fragmented

• Fragment offset– Location of packet with respect to TCP datagram

• Time to live

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP Header fields

• Protocol– Indicates protocol of IP user technology– Specified in RFC 790– E.g. TCP = 6, UDP = 21, ICMP = 1

• Checksum

• Options– Can be used to indicate source routing

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP Addresses

• An address is a unique label that helps locate an entity on a network

• 32-bit values in source and destination address fields

• Every computer on the Internet has an IP address

• Unlike MAC (Ethernet) addresses, IP addresses are assigned by network administrators

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Binary numbers overview

• Binary numbers are extremely important in data communications– IP addresses use binary numbers

• Maximum computer network sizes depend upon sizes of binary numbers

• You should be able to convert from 8-bit binary numbers to decimal and vice-versa

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Using binary numbers

• The most important use of binary numbers in this class is to assign computer addresses– In this chapter, we focus on assigning computers

with a unique label

– You should be able to determine the maximum number of addresses possible given the number of binary digits (bits) available for labeling/ addressing

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Binary numbers as labels

Bits Labels Number of labels

Formula for label count

1 0, 1 2 21

2 00, 01, 10, 11 4 22

3 000, 001, 010, 011, 100, 101, 110, 111

8 23

n 2n

ID: 0 ID: 1

ID: 00 ID: 01 ID: 10 ID: 11

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Converting from decimal to binary

128 64 32 16 8 4 2 1

• Used to compute subnet sizes, broadcast addresses etc.– You should be comfortable with binary numbers

with up to 8 digits• One technique is to fill-in-the-blanks

– Start with template below– Place 1 in the leftmost-possible position– Subtract place-value and repeat until subtraction

yields 0

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addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Place values

3 5 8 Digit

100 10 1 Decimal (Base 10) Place value

(102) (101) (100)

1 0 1 Digit

4 2 1 Binary (Base 2) Place value

(22) (21) (20)

IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Converting from decimal to binary

1

128 64 32 16 8 4 2 1

• e.g.: 133– 128 is less than 133– Hence place 1 over 128, remainder is 133 – 128 = 5

1 0 0 0 0 1

128 64 32 16 8 4 2 1

• Largest number less than 5 is 4– Hence place 1 over 4– Remainder is 5 - 4 = 1

• Largest number less than or equal to 1 is 1– Hence place 1 over 1– You get: 10000101

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Converting from decimal to binary

• Try converting the following numbers to binary– 134– 200– 240– 250

• Hint: When numbers become large, subtraction from 255 may be easier

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Converting from binary to decimal

1 1 1 0 0 0 1 1128 64 32 16 8 4 2 1

• In decimal, this number is:1*128 + 1*64 + 1*32 + 1*2 + 1*1

= 227

• Use the same template as before• Add the place values corresponding to the

locations that have 1 in the number• E.g.: 11100011

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Converting from binary to decimal

1 0 0 1 1 0 1 1128 64 32 16 8 4 2 1

• You should be comfortable working with binary numbers with up to 8 bits– e.g.: 10011011

• This number is equal to:1*128 + 0*64 + 0*32 + 1*16 + 1*8 + 0*4 + 1*2 + 1*1

= 155

• Largest possible number with 8 digits?23

IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Converting from binary to decimal

• Try converting the following numbers to decimal– 10000110– 11001000– 11110000– 11111010

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IP Header

Functions IPv6

Dotted decimal notation

• IP addresses are written in dotted decimal notation

– E.g.. 192.168.1.5

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IP Header

Functions IPv6

IP Addresses (dotted decimal notation)

• Examples

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11000000 10101000 00000001 00000101

192 . 168 . 1 5

IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP addresses – structure

• IP addresses are not assigned at random like MAC addresses– Or even on first-come-first-serve basis

• The first few address bits define the organization to which the address belongs– Remaining bits are unique to the computer (host)

within the organization

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IP Header

Functions IPv6

IP addresses – structure

• This is similar to phone numbers– (813) 974 - 6716– Tampa USF Office

• Or credit card numbers– 4 31412 34 5678 4321– Visa Bank Account number

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IP Header

Functions IPv6

IP addresses – structure

• Or zip codes– 3 36 47– State group Region Delivery address (PO)

• Visualization at http://benfry.com/zipdecode

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addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP Addresses - structure

• IP addresses are split into network part and host part

• Network part identifies the network (autonomous system) to which the address belongs– Most commonly associated with telecom carriers– Also, with large organizations such as state universities

• Host part identifies the host within the network• Host part is generally broken further into subnets

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addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP Address classes

• Network parts of IP addresses were initially classified into 3 address classes

• An organization could request an address block best suited to its needs– Class A for the largest organizations– Class B for organizations like Universities such as

USF– Class C for small businesses

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addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Class A networks

• First octet in the range 0 – 127• 24 bits for host address in each network• 7 bits for network ID• 27 = 128 possible Class A networks• Each network has 224 = 16,777,216 IP

addresses

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addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Class B and C networks

• Class B networks– First octet in the range 128-191– 16 bits for host address in each network

• Each network has 216 = 65,536 IP addresses– 14 bits for network ID

• 214 = 16,384 possible Class B networks

• Class C networks– First octet in the range 192-223– 8 bits for host address in each network

• Each network has 28 = 256 IP addresses– 21 bits for network ID

• 221 = 2,097,152 possible Class C networks

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addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Address classes0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

0 Network ID Host address within network

Class A addresses

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

1 Network ID Host address within network

Class B addresses

0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

1 Network ID Host address within network

Class C addresses

1 0

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Address classes and network addresses

• The class of an address is uniquely identifiable from the address itself

• Examples– 66.3.5.2: Class ?– 131.247.16.8: Class ?– 221.45.67.198: Class ?

• We will see in later chapters that network part of address is very important for routing

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Addresses by class

Class A addresses

Total number of hosts that can have class A addresses

= 27 * 224 = 231

= 2,147,483,648 Other addresses and unallocated addresses

= 536,870,912

Class C addresses

Total number of hosts that can have class C

addresses

= 221 * 28 = 229

= 536,870,912

Class B addresses

Total number of hosts that can have class B addresses

= 214 * 216 = 230

= 1,073,741,824

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

CIDR

• Stands for Classless Inter-Domain Routing– Eliminates address classes

• Defined in RFC 1519– Focus here on addressing component of RFC

• Aims to solve two problems with classed addresses

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addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

CIDR

• Address blocks can be of arbitrary length– Block sizes of any power of 2 are available

• Primary beneficiaries of CIDR addressing are medium-sized organizations– Too big for Class C (~250 hosts), too small for Class

B (~65,000 hosts)

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

CIDR notation

• Address class is no longer uniquely identifiable from the address– We must find a way of telling routers the size of

the network part of the address– Done by including a number along with the

network address

– E.g. 73.5.0.0/ 17

IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

CIDR notation

• In the above example, the first 17 bits of the address are the network part

• You can search for more example CIDR address blocks at http://www.arin.net

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addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Obtaining IP addresses

• Regional registries– IP addresses distributed around the globe

• American Registry for Internet Numbers

• RIPE Network Coordination Centre (RIPE NCC)– Europe, the Middle East and Central Asia

• Asia-Pacific Network Information Centre (APNIC)– Asia and the Pacific region

• Latin American and Caribbean Internet Address Registry (LACNIC)

• African Network Information Centre (AfriNIC)

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IP Header

Functions IPv6

Obtaining IP addresses

• Registries prefer allocating large address pools to large carriers

• RFC 2050– Sec 2.1: ISPs who exchange routing information with

other ISPs at multiple locations and operate without default routing may request space directly from the regional registry in its geographical area

• Most organizations will obtain IP addresses from these carriers (ISPs)

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

Obtaining IP addresses

• Requesting initial allocation from ARIN– http://www.arin.net/registration/guidelines/ipv4_

initial_alloc.html• ARIN allocation pre-requisites

– http://www.arin.net/policy/nrpm.html#four• Assigned network addresses

– RFC 790 (1981)– http://www.iana.org/assignments/ipv4-address-sp

ace (current)

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addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP version 6

• Current version of IP is 4– IPv4 has one major limitation

– Total IPv4 address pool• 232 = 4,294,967,296 (about 4 billion)• Approx 1 IP address per person• But allocation is not very efficient

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP version 6 overview

• IPv6 defined in RFC 2460• Primarily expands source and destination

address fields• Also simplifies packet processing at routers

– Eliminates header checksum

• And adds some telecom carrier-friendly features such as flow labels

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP version 6 address pool

• IP version 6 is mainly intended to eliminate shortage of IP addresses– Total address pool = 2128 addresses =

• 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses (340 * 1036)

• Surface area of earth = 510,007,200,000,000 m2 (510*1012 m2)– 600 billion trillion IP addresses per square meter

of the Earth’s surface (including oceans, deserts etc)

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP version 6 header

Version Traffic class Flow label

Payload length Next header Hop limit

Source address

Destination address

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Note: Each tick mark represents a bit position47

IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP version 6 header fields

• Version– 6

• Traffic class– Similar to IPv4 TOS field– Allows sender to specify service priority for data

• Flow label– Allows sender to label a few packets for special

handling

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IPIP

addressesObtaining IP addressesCIDR

IP Header

Functions IPv6

IP version 6 header fields

• Payload length– Length of data in packet– Similar to total length field in IPv4

• Next header– Transport layer user of IP

• Same as protocol field in IPv4• Specified in RFC 1700

• Hop limit– Same as TTL field of IPv4

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Summary

• Functions of IP• Why different parts of IP addresses• Why CIDR• Obtaining IP addresses• IP version 6

Case study – networks in the retail sector

• Both Wal-Mart and K-Mart started in 1962• K-Mart grew rapidly at first

– 250 stores in 1967, compared to 18 Wal-Marts– Each K-Mart store had 6 times the revenue of a

Wal-Mart store• 2002

– K-Mart filed for bankruptcy– For the first time, Wal-Mart was the largest

company in America by revenue

Among other factors

• Wal-Mart relied on IT– First computer network using phone lines in 1977

• To improve inventory refills

– Satellite network in 1987• Cut credit card processing time by half

– EDI, RetailLink• K-Mart relied on managerial expertise

– Used spreadsheets to track supply and demand

Hands-on exercise

• ipconfig for IP addresses• ARIN for address block ownership• ping

– Round trip times– Pinging to check network connectivity

Network design

• Estimate of IP address requirements

• Address block requirement