Network Layer Addressing in TCP/IP

May 20, 2015May 20, 2015 BMK, AKGEC, GhaziabadBMK, AKGEC, Ghaziabad 11
Computer NetworksComputer Networks
(ECS - 601)(ECS - 601)
BM KalraBM Kalra
Professor and HoDProfessor and HoD
Computer Science and EngineeringComputer Science and Engineering
Ajay Kumar Garg Engineering College, GhaziabadAjay Kumar Garg Engineering College, Ghaziabad

Lecture 33Lecture 33
(20 Mar 2015)(20 Mar 2015)
Network LayerNetwork Layer
AddressingAddressing

OSI Model - Summary of layersOSI Model - Summary of layers

Network LayerNetwork Layer
 Responsible for source to destination delivery – data link layerResponsible for source to destination delivery – data link layer
oversees the delivery of packet between two systems on the sameoversees the delivery of packet between two systems on the same
network (link)network (link)
 To provide internetworking – to move the packet through differentTo provide internetworking – to move the packet through different
networksnetworks
 Provides logical addressing – IP Address – network layer adds aProvides logical addressing – IP Address – network layer adds a
header that includes the logical addresses of the sender and theheader that includes the logical addresses of the sender and the
receiverreceiver
 Uses IP in TCP/IP protocol suiteUses IP in TCP/IP protocol suite
 Delivery of individual packets from the source to the destination hostDelivery of individual packets from the source to the destination host
 A delivery mechanism used by TCP/UDPA delivery mechanism used by TCP/UDP
 unreliable and connectionless datagram protocolunreliable and connectionless datagram protocol
 provides a best effort delivery serviceprovides a best effort delivery service
 Provides no error control or flow controlProvides no error control or flow control
 Only provides error detectionOnly provides error detection
 IP supporting protocolsIP supporting protocols
 ARP – Address Resolution ProtocolARP – Address Resolution Protocol
 RARP – Reverse Address Resolution ProtocolRARP – Reverse Address Resolution Protocol
 ICMP – Internet Control Message ProtocolICMP – Internet Control Message Protocol
 IGMP – Internet Group Message ProtocolIGMP – Internet Group Message Protocol

Links Between Two HostsLinks Between Two Hosts

Network layer in anNetwork layer in an
internetworkinternetwork

Network Layer at Source &Network Layer at Source &
DestinationDestination

Network Layer at the RouterNetwork Layer at the Router

AddressesAddresses
AnalogyAnalogy
If you want to know any info about me fromIf you want to know any info about me from
somebody or want to send some info to mesomebody or want to send some info to me
How do you identify me?How do you identify me?
What is my identity?What is my identity?
My NameMy Name
My AddressMy Address
To send information on the net-To send information on the net-
whom to send?whom to send?
How do you identify a machine onHow do you identify a machine on
the network?the network?

AddressesAddresses
 FlatFlat
 voter-idvoter-id
 i-card numbersi-card numbers
 HierarchicalHierarchical
 Postal PIN numbersPostal PIN numbers
 International telephone numberingInternational telephone numbering
schemescheme
 What is a MAC address?What is a MAC address?

Flat AddressingFlat Addressing
 In a flat routing infrastructure, each network ID isIn a flat routing infrastructure, each network ID is
represented individually in the routing table.represented individually in the routing table.
 The network IDs have no network/subnet structureThe network IDs have no network/subnet structure
and cannot be summarized.and cannot be summarized.
 RIP-based IPX internetworks use flat networkRIP-based IPX internetworks use flat network
addressing and have a flat routing infrastructure.addressing and have a flat routing infrastructure.
.

IP Address HierarchyIP Address Hierarchy
 Does a telephone switch in California know howDoes a telephone switch in California know how
to reach a specific phone in Virginia?to reach a specific phone in Virginia?
(1-703-555-1212)(1-703-555-1212)

(1-703-555-1212)(1-703-555-1212)
Long (remote)
distance
Local
office
California
Path to 1
(A number
indicates
destination
is remote)

(1-703-555-1212)(1-703-555-1212)
Long (remote)
distance
Long distance
Virginia
Path to 703
(An area code
summarizes
an area in VA)
Local
office
California
Path to 1
(A number
indicates
destination
is remote)

 Does a telephone switch in California know how toDoes a telephone switch in California know how to
reach a specific phone in Virginia?reach a specific phone in Virginia?
(1-703-555-1212)(1-703-555-1212)
Long (remote)
distance
Long distance
Virginia
Path to 703
(An area code
summarizes
an area in VA)
Path to 555
(A prefix
summarizes
a smaller area
in VA)
Local office
Alexandria
Local
office
California
Path to 1
(A number
indicates
destination
is remote)

 Does a telephone switch in California know how to reach aDoes a telephone switch in California know how to reach a
specific phone in Virginia?specific phone in Virginia?
(1-703-555-1212)(1-703-555-1212)
Long (Remote)-
Distance
Long-Distance
Virginia
Path to 703
(An Area Code
Summarizes
an Area in VA)
Path to 555
(A Prefix
Summarizes
a Smaller Area
in VA)
Path to 1212
(Number)
Local Office
Alexandria
Local
Office
Aunt JudyCalifornia
Path to 1
(A Number
Indicates
Destination
Is Remote)

Benefits of HierarchicalBenefits of Hierarchical
 Reduced number of route table entriesReduced number of route table entries
Summarize multiple addresses into routeSummarize multiple addresses into route
summariessummaries
 Efficient allocation of addressesEfficient allocation of addresses
Contiguous address assignment allows you toContiguous address assignment allows you to
use all possible addressesuse all possible addresses

Hierarchical AddressingHierarchical Addressing
 groups of network IDs can be represented as a single
routing table entry through route summarization
 The network IDs in a hierarchical internetwork have a
network/subnet/sub-subnet structure
 A routing table entry for the highest level (the network)
is also the route used for the subnets and sub-subnets
of the network
 simplifes routing tables and lower the amount of
routing information that is exchanged, but they require
more planning
 IP implements hierarchical network addressing, and IP
internetworks can have a hierarchical routing
structure

AddressesAddresses
Each communication endpoint mustEach communication endpoint must
have an address.have an address.
Consider 2 processesConsider 2 processes
communicating over an internet:communicating over an internet:
 the network must be specifiedthe network must be specified
 the host must be specifiedthe host must be specified
 the process must be specified.the process must be specified.

AddressesAddresses
Physical LayerPhysical Layer: no address necessary: no address necessary
Data Link LayerData Link Layer - address must be able toaddress must be able to
select any host on the network.select any host on the network.
Network LayerNetwork Layer - address must be able toaddress must be able to
provide information to enable routing.provide information to enable routing.
Transport LayerTransport Layer - address must identify theaddress must identify the
destination process.destination process.

Addresses in TCP/IPAddresses in TCP/IP

AddressesAddresses
Three typesThree types
 Port AddressPort Address
 Layer 4 addressLayer 4 address
 For running different applicationsFor running different applications
 Logical AddressLogical Address
 Layer3 addressLayer3 address
 IP address and it is set by the operating systemIP address and it is set by the operating system
 Changes with location changeChanges with location change
 Physical AddressPhysical Address
 Layer2 addressLayer2 address
 MAC addressMAC address
 generated by the manufacturergenerated by the manufacturer
 The MAC address is unique In a Local Area Network (LAN)The MAC address is unique In a Local Area Network (LAN)
 Fixed – does not changeFixed – does not change

Logical & Physical AddressesLogical & Physical Addresses
AnalogyAnalogy
 My Name: Physical AddressMy Name: Physical Address
 My Home Address: Logical AddressMy Home Address: Logical Address

IPv4 AddressingIPv4 Addressing
An IPv4 address is a 32-bit addressAn IPv4 address is a 32-bit address
thatthat uniquelyuniquely andand universallyuniversally definesdefines
the connection of a device (forthe connection of a device (for
example, a computer or a router) toexample, a computer or a router) to
the Internetthe Internet
 UniqueUnique – two devices on the internet– two devices on the internet
can never have the same address at thecan never have the same address at the
same timesame time
 UniversalUniversal – addressing system must be– addressing system must be
accepted by any host that wants to beaccepted by any host that wants to be
connected to the Internetconnected to the Internet

 Logical AddressLogical Address
 Layer3 AddressingLayer3 Addressing
 Example - IPv4/IPv6Example - IPv4/IPv6
 IPv4 addresses are unique & universalIPv4 addresses are unique & universal
 Two Level Hierarchical AddressingTwo Level Hierarchical Addressing
 Network id + Host idNetwork id + Host id
 IPv4 – 32 bit addressing systemIPv4 – 32 bit addressing system
 223232
= 4,294,967,296(more than 4 Billion IP Addresses)= 4,294,967,296(more than 4 Billion IP Addresses)
Network IDNetwork ID
(8 to 24 bits)(8 to 24 bits)
Host IDHost ID
(24 to 8 bits)(24 to 8 bits)

IPv4 /Internet/Global /LogicalIPv4 /Internet/Global /Logical
AddressAddress

The IPv4 addresses are unique
and universal.
NoteNote

The address space of IPv4 is
232
or 4,294,967,296 (more than 4 billion)
NoteNote

Layer 3 AddressesLayer 3 Addresses
Network IDNetwork ID
 Assigned byAssigned by
ARINARIN
(www.arin.net)(www.arin.net)
 Identifies theIdentifies the
network tonetwork to
which a devicewhich a device
is attached.is attached.
 May beMay be
identified byidentified by
one, two, orone, two, or
three of thethree of the
first threefirst three
octets.octets.
Host IDHost ID
 Assigned by aAssigned by a
networknetwork
administrator.administrator.
 Identifies the specificIdentifies the specific
device on thatdevice on that
network.network.
 May be identified byMay be identified by
one, two, or three ofone, two, or three of
the last three octets.the last three octets.

IP Address: NotationIP Address: Notation
Binary NotationBinary Notation
 In binary notation, the IPv4 address is displayed as 32 bits.In binary notation, the IPv4 address is displayed as 32 bits.
 Each octet is often referred to as a byte. So it is common to hear anEach octet is often referred to as a byte. So it is common to hear an
IPv4 address referred to as a 32-bit address or a 4-byte address. (MACIPv4 address referred to as a 32-bit address or a 4-byte address. (MAC
Address – 6 bytes)Address – 6 bytes)
 The following is an example of an IPv4 address in binary notation:The following is an example of an IPv4 address in binary notation:
01110101 10010101 00011101 0000001001110101 10010101 00011101 00000010
Dotted-Decimal NotationDotted-Decimal Notation
 To make the IPv4 address more compact and easier to read, InternetTo make the IPv4 address more compact and easier to read, Internet
addresses are usually written in decimal form with a decimal pointaddresses are usually written in decimal form with a decimal point
(dot) separating the bytes.(dot) separating the bytes.
 The following is the dotted-decimal notation of the above address:The following is the dotted-decimal notation of the above address:
117.149.29.2117.149.29.2
 One octet – 8 bitsOne octet – 8 bits
 total numbers – 2total numbers – 288
=256 (0-255)=256 (0-255)
 So, highest number 255So, highest number 255

Dotted-decimal notation andDotted-decimal notation and
binary notation for an IPv4binary notation for an IPv4
addressaddress

Dotted - Decimal NotationDotted - Decimal Notation
Network layer addresses are 32 bits longNetwork layer addresses are 32 bits long
1000010010100011100000000001000110000100101000111000000000010001
This binary number can be divided into fourThis binary number can be divided into four
octetsoctets
10000100 10100011 10000000 0001000110000100 10100011 10000000 00010001
Each octet (or byte) can be converted toEach octet (or byte) can be converted to
decimal numberdecimal number
132 163 128 17132 163 128 17
Finally the address can be written in dottedFinally the address can be written in dotted
decimal notationdecimal notation
132.163.128.17132.163.128.17

Example 19.1Example 19.1
Change the following IPv4 addresses fromChange the following IPv4 addresses from
binary notation to dotted-decimal notation.binary notation to dotted-decimal notation.
SolutionSolution
We replace each group of 8 bits with itsWe replace each group of 8 bits with its
equivalent decimal number and add dots forequivalent decimal number and add dots for
separation.separation.

Change the following IPv4 addresses fromChange the following IPv4 addresses from
dotted-decimal notation to binary notation.dotted-decimal notation to binary notation.
SolutionSolution
We replace each decimal number with itsWe replace each decimal number with its
binary equivalentbinary equivalent

Find the error, if any, in the following IPv4 addresses.Find the error, if any, in the following IPv4 addresses.
a.a. 111.56.045.78111.56.045.78
b.b. 221.34.7.8.20221.34.7.8.20
c.c. 75.45.301.1475.45.301.14
d.d. 11100010.23.14.6711100010.23.14.67
SolutionSolution
a.a. There must be no leading zero (There must be no leading zero (0045).45).
b.b. There can be no more than four numbers.There can be no more than four numbers.
c.c. Each number needs to be less than or equal to 255.Each number needs to be less than or equal to 255.
d.d. A mixture of binary notation and dotted-decimalA mixture of binary notation and dotted-decimal
notation is not allowed.notation is not allowed.

Classful IP AddressesClassful IP Addresses
Three major organizationsThree major organizations
Large OrganizationLarge Organization with a largewith a large
number of attached hosts or routersnumber of attached hosts or routers
Midsize organizationMidsize organization with tens andwith tens and
thousands of attached hosts orthousands of attached hosts or
routersrouters
Small organizationSmall organization with a smallwith a small
number of attached hosts or routersnumber of attached hosts or routers

In classful addressing, the address
space is divided into five classes:
A, B, C, D, and E.
NoteNote

Three major classesThree major classes
Class AClass A: Small number of Networks: Small number of Networks
– Large number of hosts– Large number of hosts
Class BClass B: Medium number of: Medium number of
Networks – Medium number of hostsNetworks – Medium number of hosts
Class CClass C: Large number of Networks: Large number of Networks
– Small number of hosts– Small number of hosts

N – NetworkN – Network
H – HostH – Host
FirstFirst
OctetOctet
SecondSecond
OctetOctet
ThirdThird
OctetOctet
FourthFourth
OctetOctet
Class AClass A NN HH HH HH
Class BClass B NN NN HH HH
Class CClass C NN NN NN HH
Class DClass D
Class EClass E

Classes – Binary & DottedClasses – Binary & Dotted
DecimalDecimal
Class D: for multicastingClass D: for multicasting
Class E: for future/research useClass E: for future/research use

First OctetFirst Octet
 Class AClass A
 00 00000000000000 00
 00 11111111111111 127127
 Class BClass B
 1010 000000000000 128128
 1010 111111111111 191191
 Class CClass C
 110110 0000000000 192192
 110110 1111111111 223223
 Class D:Class D: MulticastMulticast
 11101110 00000000 224224
 11101110 11111111 239239
 Class E:Class E: ExperimentalExperimental
 11111111 00000000 240240
 11111111 11111111 255255

Address Class UsageAddress Class Usage
AddressAddress classes A, B, and Cclasses A, B, and C are available forare available for
Internet useInternet use
Class DClass D addresses are used foraddresses are used for multicastingmulticasting
 Some Class D multicast addresses areSome Class D multicast addresses are used byused by
routing protocolsrouting protocols
OSPF—224.0.0.5, 224.0.0.6OSPF—224.0.0.5, 224.0.0.6
RIPv2—224.0.0.9RIPv2—224.0.0.9
EIGRP—224.0.0.10EIGRP—224.0.0.10
 Other Class D multicast addresses are used byOther Class D multicast addresses are used by
videoconferencing or other applicationsvideoconferencing or other applications
Class EClass E addresses are reserved for future useaddresses are reserved for future use
and for research purposesand for research purposes

What Class?What Class?
 How do you know what class an IP address is in?How do you know what class an IP address is in?
For Dotted Decimal AddressFor Dotted Decimal Address
 If the first octet is between:If the first octet is between:
 0 – 1270 – 127 Class A addressesClass A addresses
 128 – 191128 – 191 Class B AddressesClass B Addresses
 192 – 223192 – 223 Class C AddressesClass C Addresses
 224 – 239224 – 239 Class D AddressesClass D Addresses
 240 – 255240 – 255 Class E AddressesClass E Addresses
For Binary IP AddressFor Binary IP Address
 The first bit is 0The first bit is 0 Class A AddressClass A Address
 The first 2 bits are 10The first 2 bits are 10 Class B AddressClass B Address
 First three bits are 110First three bits are 110 Class C AddressClass C Address
 First four bits are 1110First four bits are 1110 Class D AddressClass D Address
 First four bits are 1111First four bits are 1111 Class E AddressClass E Address

Find the class of each addressFind the class of each address
a.a. 000000001 00001011 00001011 111011110000001 00001011 00001011 11101111
b.b. 11011000001 10000011 00011011 1111111100001 10000011 00011011 11111111
c.c. 1414.23.120.8.23.120.8
d.d. 252252.5.15.111.5.15.111
SolutionSolution
a.a. The first bit is 0. This is a class A address.The first bit is 0. This is a class A address.
b.b. The first 2 bits are 1; the third bit is 0. This is a class CThe first 2 bits are 1; the third bit is 0. This is a class C
address.address.
c.c. The first byte is 14; the class is A.The first byte is 14; the class is A.
d.d. The first byte is 252; the class is E.The first byte is 252; the class is E.

Number of NetworksNumber of Networks
Number of networks in each classNumber of networks in each class
 Class A has 128 networks (0 to 127)Class A has 128 networks (0 to 127)
 Class B has 16,384 networksClass B has 16,384 networks
 Class C has 2,097,152 networksClass C has 2,097,152 networks

Number of HostsNumber of Hosts
Maximum number of hosts vary for eachMaximum number of hosts vary for each
classclass
 Class A has 16,777,214 available hosts (2Class A has 16,777,214 available hosts (22424
–2)–2)
 Class B has 65,534 available hosts (2Class B has 65,534 available hosts (21616
–2)–2)
 Class C has 254 available hosts (2Class C has 254 available hosts (288
–2)–2)
The first address in each network isThe first address in each network is
reserved for thereserved for the Network AddressNetwork Address (all zeros)(all zeros)
and the last address is reserved for theand the last address is reserved for the
Broadcast AddressBroadcast Address (all ones)(all ones)

No. of blocks and block sizeNo. of blocks and block size

In classful addressing, a large part of
the available addresses were wasted.
NoteNote

(20 Mar 2015)(20 Mar 2015)
IP AddressingIP Addressing

Reserved AddressesReserved Addresses
Network Address (wire address)Network Address (wire address) – This is an– This is an
IP address that ends with binaryIP address that ends with binary 0s in all0s in all
host bits.host bits.
Class A Network Address example:Class A Network Address example:
 113.0.0.0113.0.0.0
Hosts on a network can only communicateHosts on a network can only communicate
directlydirectly with other hosts if they have thewith other hosts if they have the
same network ID.same network ID.
If they don’t, they will not be able toIf they don’t, they will not be able to
communicate unless there iscommunicate unless there is another deviceanother device
connecting the networks.connecting the networks.

Broadcast AddressBroadcast Address – is used to send data– is used to send data
to all of the devices on a network.to all of the devices on a network.
Broadcast IP addresses end with binaryBroadcast IP addresses end with binary 1s1s
in the host partin the host part of the address.of the address.
Class B Broadcast Address example:Class B Broadcast Address example:
 176.10.255.255176.10.255.255
(Remember decimal 255 = binary 11111111)(Remember decimal 255 = binary 11111111)

Special AddressSpecial Address
 Host ID “all 0s” is reserved to refer toHost ID “all 0s” is reserved to refer to networknetwork
numbernumber
 192.168.100.0192.168.100.0
 158.108.0.0158.108.0.0
 18.0.0.018.0.0.0
 Host ID “all 1s” is reserved toHost ID “all 1s” is reserved to broadcastbroadcast to allto all
hosts on a specific networkhosts on a specific network
 192.168.100.255192.168.100.255
 158.108.255.255158.108.255.255
 18.255.255.25518.255.255.255
 Address 0.0.0.0 means “Address 0.0.0.0 means “default routedefault route””
 Address 127.0.0.0 means “Address 127.0.0.0 means “this nodethis node””
 Address 127.0.0.1Address 127.0.0.1 ((local loopbacklocal loopback). Message sent). Message sent
to this address will never leave the local hostto this address will never leave the local host
 Address 255.255.255.255 is reserveAddress 255.255.255.255 is reservedd to broadcastto broadcast
to every host on the local network (limitedto every host on the local network (limited
broadcast)broadcast)

Netid and HostidNetid and Hostid
Netid and host id are of varying length –Netid and host id are of varying length –
depending on class of the addressdepending on class of the address
FirstFirst
OctetOctet
SecondSecond
OctetOctet
ThirdThird
OctetOctet
FourthFourth
OctetOctet
Class AClass A NN HH HH HH
Class BClass B NN NN HH HH
Class CClass C NN NN NN HH
Class DClass D
Class EClass E

Netid and HostidNetid and Hostid

MaskMask
 Although the length of the netid and hostid (inAlthough the length of the netid and hostid (in
bits) is predetermined in classful addressing,bits) is predetermined in classful addressing,
 we can also use a mask (also called the defaultwe can also use a mask (also called the default
mask), a 32-bit number made of contiguous 1smask), a 32-bit number made of contiguous 1s
followed by contiguous 0s.followed by contiguous 0s.
 The mask can help us to find the netid and theThe mask can help us to find the netid and the
hostid.hostid.
 For example, the mask for a class A address hasFor example, the mask for a class A address has
eight 1s, which means the first 8 bits of anyeight 1s, which means the first 8 bits of any
address in class A define the netid; the next 24address in class A define the netid; the next 24
bits define the hostid.bits define the hostid.
 The concept does not apply to classes D and E.The concept does not apply to classes D and E.

MaskingMasking

Default Mask for classfulDefault Mask for classful
addressingaddressing
 The last column shows the mask in the form /nThe last column shows the mask in the form /n
where n can be 8, 16, or 24 in classful addressing.where n can be 8, 16, or 24 in classful addressing.
 This notation is also calledThis notation is also called slash notationslash notation oror
Classless Interdomain RoutingClassless Interdomain Routing (CIDR) notation.(CIDR) notation.
 Classful addressing is a special case of classlessClassful addressing is a special case of classless
addressing.addressing.

Crisis & SolutionsCrisis & Solutions

Flaw in Classful AddressFlaw in Classful Address
We can see the flaw in this design.We can see the flaw in this design.
A block in class A address is too large forA block in class A address is too large for
almost any organizationalmost any organization
A block in class B is also very large,A block in class B is also very large,
probably too large for any of theprobably too large for any of the
organizations that received a class B block.organizations that received a class B block.
A block in class C is probably too small.A block in class C is probably too small.
A and B always wasted. But C is always notA and B always wasted. But C is always not
enuff!!!enuff!!!

Issues with IP AddressingIssues with IP Addressing
 IP address exhaustionIP address exhaustion
 Routing table growthRouting table growth
U N I V E R S I T YU N I V E R S I T Y
Internet

IP Addressing SolutionsIP Addressing Solutions
SubnettingSubnetting (RFCs 950, 1812)(RFCs 950, 1812)
Private AddressesPrivate Addresses (RFC 1918)(RFC 1918)
 Network Address Translation (NAT)Network Address Translation (NAT)
(RFC 1631)(RFC 1631)
Classless Interdomain Routing (CIDR)Classless Interdomain Routing (CIDR)
(RFCs 1518, 1519, 2050)(RFCs 1518, 1519, 2050)
Route summarizationRoute summarization (RFC 1518)(RFC 1518)
Variable Length Subnet MaskingVariable Length Subnet Masking
(VLSM)(VLSM) (RFC 1812)(RFC 1812)

SubnettingSubnetting

Basics of SubnettingBasics of Subnetting
 Subnetwork is a smaller divisions of a networksSubnetwork is a smaller divisions of a networks
 A larger network is split into several smaller partsA larger network is split into several smaller parts
for internal use – say different departments of afor internal use – say different departments of a
college – but still act like a single network to thecollege – but still act like a single network to the
outside worldoutside world

Basically without subnetting, most ofBasically without subnetting, most of
organization is limited to two levelsorganization is limited to two levels
of hierarchyof hierarchy
 In this case, the hosts cannot beIn this case, the hosts cannot be
organized into groups, and all of theorganized into groups, and all of the
hosts are at the same level.hosts are at the same level.
 As a result the organization has oneAs a result the organization has one
network with many many hostsnetwork with many many hosts

A Network with Two Levels ofA Network with Two Levels of
HierarchyHierarchy

To make a network more organize,To make a network more organize,
three levels of hierarchy isthree levels of hierarchy is
implemented.implemented.
Subnetting creates an intermediateSubnetting creates an intermediate
level of hierarchy in the IP addressinglevel of hierarchy in the IP addressing
system.system.
Now we have 3 levels:Now we have 3 levels:
 NetidNetid
 subnetid, andsubnetid, and
 hostid.hostid.

Subnet AddressesSubnet Addresses
 Changing from 2 Level hierarchy to 3 LevelChanging from 2 Level hierarchy to 3 Level
hierarchyhierarchy
 Include Class A, B, or C network portion plus aInclude Class A, B, or C network portion plus a
subnet field and a host field.subnet field and a host field.
 Bits are borrowed from the host field and areBits are borrowed from the host field and are
designated as the subnet field.designated as the subnet field.
NetworkNetwork SubnetSubnet HostHost
NetworkNetwork HostHost

A Network with Three Levels ofA Network with Three Levels of
HierarchyHierarchy

Basics of SubnettingBasics of Subnetting
They provide addressing flexibilityThey provide addressing flexibility
Less wastage of IP addressesLess wastage of IP addresses
Better logical organizationBetter logical organization
Provides a logical network structure thatProvides a logical network structure that
is hidden from the outside worldis hidden from the outside world
A.K.A. subnetsA.K.A. subnets
Subnet addresses are assigned locally,Subnet addresses are assigned locally,
usually by a network administrator.usually by a network administrator.
Subnets reduce a broadcast domain.Subnets reduce a broadcast domain.
RFC 950 (1985)RFC 950 (1985)

SupernettingSupernetting
 The time came when most of the class A and class BThe time came when most of the class A and class B
addresses were depleted; however, here was still aaddresses were depleted; however, here was still a
huge demand for midsize blocks.huge demand for midsize blocks.
 The size of a class C block with a maximum number ofThe size of a class C block with a maximum number of
256 addresses did not satisfy the needs of most256 addresses did not satisfy the needs of most
organizations.organizations.
 Even a midsize organization needed more addresses.Even a midsize organization needed more addresses.
 One solution was supernetting.One solution was supernetting.
 In supernetting, an organization can combine severalIn supernetting, an organization can combine several
class C blocks to create a larger range of addresses.class C blocks to create a larger range of addresses.
 In other words, several networks are combined toIn other words, several networks are combined to
create a supernetwork or a supernet.create a supernetwork or a supernet.

SupernettingSupernetting
 An organization can apply for a set of class C blocksAn organization can apply for a set of class C blocks
instead of just one.instead of just one.
 For example, an organization that needs 1000For example, an organization that needs 1000
addresses can be granted four contiguous class Caddresses can be granted four contiguous class C
blocks.blocks.
 The organization can then use these addresses toThe organization can then use these addresses to
create one supernetwork.create one supernetwork.
 Supernetting decreases the number of 1s in the mask.Supernetting decreases the number of 1s in the mask.
 For example, if an organization is given four class CFor example, if an organization is given four class C
addresses, the mask changes from /24 to /22.addresses, the mask changes from /24 to /22.
 We will see that classless addressing eliminated theWe will see that classless addressing eliminated the
need for supernetting.need for supernetting.

Addresses with and withoutAddresses with and without

Subnet MaskSubnet Mask
To implement subnetting, mainTo implement subnetting, main
router needs a subnet mask – thatrouter needs a subnet mask – that
indicates the network + subnetindicates the network + subnet
portion and the host portionportion and the host portion
Subnet mask is also 32 bit longSubnet mask is also 32 bit long
Written in dotted decimal notationWritten in dotted decimal notation
with a slash followed by the numberwith a slash followed by the number
of bits in the network + subnet partof bits in the network + subnet part

Subnet MaskSubnet Mask
Subnet mask can be written asSubnet mask can be written as
255.255.252.0255.255.252.0
Alternative notationAlternative notation /22/22 – indicates– indicates
that the subnet mask is 22 bit longthat the subnet mask is 22 bit long

Classful addressing, which is almost
obsolete, is replaced with classless
addressing.
Note

ClasslessClassless
Interdomain Routing (CIDR)Interdomain Routing (CIDR)
“cider”“cider”

Classless AddressingClassless Addressing
 To overcome address depletion and give more organizationsTo overcome address depletion and give more organizations
access to the Internet, classless addressing was designed andaccess to the Internet, classless addressing was designed and
implemented.implemented.
 In this scheme,In this scheme, there are no classesthere are no classes, but the addresses are still, but the addresses are still
granted in blocks.granted in blocks.
Address BlocksAddress Blocks
 In classless addressing, when an entity, small or large, needsIn classless addressing, when an entity, small or large, needs
to be connected to the Internet, it is granted a block (range) ofto be connected to the Internet, it is granted a block (range) of
addresses.addresses.
 The size of the block (the number of addresses) varies basedThe size of the block (the number of addresses) varies based
on the nature and size of the entity.on the nature and size of the entity.
 For example,For example,
 a household may be given only two addresses;a household may be given only two addresses;
 a large organization may be given thousands of addressesa large organization may be given thousands of addresses
 an ISP, as the Internet service provider, may be given thousandsan ISP, as the Internet service provider, may be given thousands
or hundreds of thousands based on the number of customers itor hundreds of thousands based on the number of customers it
may serve.may serve.

Classless AddressingClassless Addressing
To simplify the handling of addresses,To simplify the handling of addresses,
the Internet authorities impose threethe Internet authorities impose three
restrictions on classless addressrestrictions on classless address
blocks:blocks:
 1. The addresses in a block must be1. The addresses in a block must be
contiguous, one after another.contiguous, one after another.
 2. The number of addresses in a block2. The number of addresses in a block
must be a power of 2 (I, 2, 4, 8, ... ).must be a power of 2 (I, 2, 4, 8, ... ).
 3. The first address must be evenly3. The first address must be evenly
divisible by the number of addresses.divisible by the number of addresses.

Figure 19.3 shows a block ofFigure 19.3 shows a block of
addresses, in both binary and dotted-addresses, in both binary and dotted-
decimal notation, granted to a smalldecimal notation, granted to a small
business that needs 16 addresses.business that needs 16 addresses.

Figure 19.3, A block of 16 addresses granted to a small organizationFigure 19.3, A block of 16 addresses granted to a small organization
 We can see that the restrictions are applied to this block.We can see that the restrictions are applied to this block.
 The addresses are contiguous.The addresses are contiguous.
 The number of addresses is a power of 2 (16 = 24), andThe number of addresses is a power of 2 (16 = 24), and
 The first address is divisible by 16.The first address is divisible by 16.
 The first address, when converted to a decimal number, isThe first address, when converted to a decimal number, is
3,440,387,360, which when divided by 16 results in 215,024,2103,440,387,360, which when divided by 16 results in 215,024,210

MaskMask
A better way to define a block of addresses isA better way to define a block of addresses is
to select any address in the block and theto select any address in the block and the
mask.mask.
As we discussed before, a mask is a 32-bitAs we discussed before, a mask is a 32-bit
number in which thenumber in which the n leftmost bits are 1sn leftmost bits are 1s
and the 32 - n rightmost bits are 0s.and the 32 - n rightmost bits are 0s.
However, in classless addressing the maskHowever, in classless addressing the mask
for a block can take any value from 0 to 32.for a block can take any value from 0 to 32.
It is very convenient to give just the value ofIt is very convenient to give just the value of
n preceded by a slash (CIDR notation).n preceded by a slash (CIDR notation).

MaskMask
In IPv4 addressing, a block ofIn IPv4 addressing, a block of
addresses can be defined asaddresses can be defined as
x.y.z.t /x.y.z.t /nn
in which x.y.z.t defines one of thein which x.y.z.t defines one of the
addresses and the /addresses and the /nn defines the maskdefines the mask
Where n is the number of 1s in the maskWhere n is the number of 1s in the mask
NoteNote

MaskMask
The address and the /n notationThe address and the /n notation
completely define the whole block (thecompletely define the whole block (the
first address, the last address, and thefirst address, the last address, and the
number of addresses).number of addresses).
First Address:First Address:
Network AddressNetwork Address (host part 0s)(host part 0s)
The first address in the block can beThe first address in the block can be
found by setting thefound by setting the (32 – n) rightmost(32 – n) rightmost
bitsbits in the binary notation of thein the binary notation of the
address toaddress to 0s0s..

MaskMask
The first address in the block can be
found by setting the rightmost
32 − n bits to 0s.
NoteNote

A block of addresses is granted to a smallA block of addresses is granted to a small
organization. We know that one of the addresses isorganization. We know that one of the addresses is
205.16.37.39/28205.16.37.39/28. What is the first address in the. What is the first address in the
block?block?
SolutionSolution
The binary representation of the given address isThe binary representation of the given address is
11001101 00010000 00100101 0010011111001101 00010000 00100101 00100111
If we set 32−28 rightmost bits to 0, we getIf we set 32−28 rightmost bits to 0, we get
11001101 00010000 00100101 001000011001101 00010000 00100101 0010000
oror
205.16.37.32205.16.37.32
This is actually the block shown in Figure 19.3.This is actually the block shown in Figure 19.3.

Last Address:Last Address:
Broadcast Address (host part 1s)Broadcast Address (host part 1s)
The last address in the block can beThe last address in the block can be
found by setting thefound by setting the (32 – n) rightmost(32 – n) rightmost
bitsbits in the binary notation of thein the binary notation of the
address toaddress to 1s1s..

The last address in the block can be
found by setting the rightmost
32 − n bits to 1s.
NoteNote

Find the last addressFind the last address for the block in Example 19.6.
A block of addresses is granted to a small organization.A block of addresses is granted to a small organization.
We know that one of the addresses isWe know that one of the addresses is 205.16.37.39/28205.16.37.39/28..
What is the first address in the block?What is the first address in the block?
Solution
The binary representation of the given address is
11001101 00010000 00100101 00100111
If we set 32 − 28 rightmost bits to 1, we get
11001101 00010000 00100101 00101111
or
205.16.37.47
This is actually the block shown in Figure 19.3.

Number of AddressesNumber of Addresses
The number of addresses in theThe number of addresses in the
block is the difference between theblock is the difference between the
last and first address.last and first address.
It can easily be found using theIt can easily be found using the
formulaformula 2232- n32- n
..

The number of addresses in the block
can be found by using the formula
232−n
.
NoteNote

Find the number of addresses in ExampleFind the number of addresses in Example
19.6.19.6.
A block of addresses is granted to a smallA block of addresses is granted to a small
organization. We know that one of theorganization. We know that one of the
addresses isaddresses is 205.16.37.39/28205.16.37.39/28. What is the first. What is the first
address in the block?address in the block?
SolutionSolution
formulaformula 2232- n32- n
The value of n is 28, which means thatThe value of n is 28, which means that
number of addresses is 2number of addresses is 2 32−2832−28
or 16.or 16.

 Another way to find the first address, the lastAnother way to find the first address, the last
address, and the number of addresses is toaddress, and the number of addresses is to
represent the mask as arepresent the mask as a 32-bit binary32-bit binary (or 8-digit(or 8-digit
hexadecimal) number.hexadecimal) number.
 This is particularly useful when we are writing aThis is particularly useful when we are writing a
program to find these pieces of information.program to find these pieces of information.
 In Example 19.5 the /28 can be represented asIn Example 19.5 the /28 can be represented as
11111111 11111111 11111111 1111000011111111 11111111 11111111 11110000
(twenty-eight 1s and four 0s).(twenty-eight 1s and four 0s).
FindFind
a.a. The first addressThe first address
b.b. The last addressThe last address
c.c. The number of addresses.The number of addresses.

Solution
a. The first address can be found by
ANDing the given addresses with the
mask. ANDing here is done bit by bit.
The result of ANDing 2 bits is 1 if both
bits are 1s; the result is 0 otherwise.

b.The last address can be found by ORing the
given addresses with the complement of the
mask. ORing here is done bit by bit. The
result of ORing 2 bits is 0 if both bits are 0s;
the result is 1 otherwise. The complement of
a number is found by changing each 1to 0
and each 0 to 1.

c. The number of addresses can be
found by complementing the mask,
interpreting it as a decimal number,
and adding 1 to it.

(1 4Mar 2014)(1 4Mar 2014)

Network AddressesNetwork Addresses
 When an organization is given a block ofWhen an organization is given a block of
addresses, the organization is free to allocate theaddresses, the organization is free to allocate the
addresses to the devices that need to beaddresses to the devices that need to be
connected to the Internet.connected to the Internet.
 The first address in the class, however, isThe first address in the class, however, is
normally (not always) treated as a specialnormally (not always) treated as a special
address.address.
 TheThe first address is called the network addressfirst address is called the network address
andand defines the organization networkdefines the organization network..
 It defines the organization itself to the rest of theIt defines the organization itself to the rest of the
world.world.
 The first address is the one that isThe first address is the one that is used byused by
routers to direct the message sent to therouters to direct the message sent to the
organizationorganization from the outside.from the outside.

The first address in a block is
normally not assigned to any device;
it is used as the network address that
represents the organization
to the rest of the world.
Note

Figure 19.5 Two levels of hierarchy in an IPv4 address

Two-Level Hierarchy: NoTwo-Level Hierarchy: No
 An IP address can define only two levels of hierarchyAn IP address can define only two levels of hierarchy
when not subnetted.when not subnetted.
 PrefixPrefix: The part of the address that defines the: The part of the address that defines the
network is called the prefix - Thenetwork is called the prefix - The n leftmost bitsn leftmost bits ofof
the address x.y.z.t/n define the network (organizationthe address x.y.z.t/n define the network (organization
network)network)
 SuffixSuffix: the part that defines the host is called the: the part that defines the host is called the
suffix - thesuffix - the (32-n)(32-n) rightmost bits define the particularrightmost bits define the particular
host (computer or router) to the network.host (computer or router) to the network.

Each address in the block can be
considered as a two-level
hierarchical structure:
the leftmost n bits (prefix) define
the network;
the rightmost 32 − n (suffix) bits define
the host.
NoteNote

Three-Levels of Hierarchy:Three-Levels of Hierarchy:
 An organization that is granted a large block ofAn organization that is granted a large block of
addresses may want to create clusters of networksaddresses may want to create clusters of networks
(called subnets) and divide the addresses between(called subnets) and divide the addresses between
the different subnets.the different subnets.
 The rest of the world still sees the organization asThe rest of the world still sees the organization as
one entity; however, internally there are severalone entity; however, internally there are several
subnets.subnets.
 All messages are sent to the router address thatAll messages are sent to the router address that
connects the organization to the rest of the Internet;connects the organization to the rest of the Internet;
the router routes the message to the appropriatethe router routes the message to the appropriate
subnets.subnets.
 The organization, however, needs to create small subThe organization, however, needs to create small sub
blocks of addresses, each assigned to specificblocks of addresses, each assigned to specific
subnets.subnets.
 The organization has its own mask;The organization has its own mask; each subneteach subnet
must also have its own mask.must also have its own mask.

Three-Level Hierarchy in an IPv4Three-Level Hierarchy in an IPv4
AddressAddress
subnet prefix length can differ for thesubnet prefix length can differ for the
subnetssubnets

ExampleExample
 suppose an organization is given the block 17.12.40.0/26,suppose an organization is given the block 17.12.40.0/26,
which contains 64 addresses.which contains 64 addresses.
 The organization has three offices and needs to divide theThe organization has three offices and needs to divide the
addresses into three sub blocks of 32, 16, and 16 addresses.addresses into three sub blocks of 32, 16, and 16 addresses.
SolutionSolution
 We canWe can find the new masksfind the new masks by using the following arguments:by using the following arguments:
 1. Suppose the mask for the first subnet is n1, then 21. Suppose the mask for the first subnet is n1, then 232- n132- n1
must bemust be
32, which means that n1 =27.32, which means that n1 =27.
 2. Suppose the mask for the second subnet is n2, then 22. Suppose the mask for the second subnet is n2, then 232- n232- n2
mustmust
be 16, which means that n2 = 28.be 16, which means that n2 = 28.
 3. Suppose the mask for the third subnet is n3, then 23. Suppose the mask for the third subnet is n3, then 232- n332- n3
must bemust be
16, which means that n3 =28.16, which means that n3 =28.
 This means that we have the masksThis means that we have the masks 27, 28, 2827, 28, 28 with thewith the
organization mask beingorganization mask being 2626..
 Figure shows one configuration for the above scenario.Figure shows one configuration for the above scenario.
Three-Levels of Hierarchy:Three-Levels of Hierarchy:

Configuration & Addresses: SubnettedConfiguration & Addresses: Subnetted
NetworkNetwork

Finding subnet addresses from oneFinding subnet addresses from one
of the addresses in the subnet.of the addresses in the subnet.
In subnet 1In subnet 1, the address 17.12.14.29/27 can, the address 17.12.14.29/27 can
give us the subnet address if we use thegive us the subnet address if we use the
subnet mask /27subnet mask /27
HostHost::
00010001 00001100 00001110 0001110100010001 00001100 00001110 00011101
ANDing with MaskANDing with Mask: /27 (27 1s): /27 (27 1s)
11111111 11111111 11111111 1110000011111111 11111111 11111111 11100000
We get theWe get the subnetsubnet::
00010001 00001100 00001110 0000000000010001 00001100 00001110 00000000
17.12.14.017.12.14.0

subnet mask /28subnet mask /28
HostHost::
00010001 00001100 00001110 0010110100010001 00001100 00001110 00101101
11111111 11111111 11111111 1111000011111111 11111111 11111111 11110000
We get the subnetWe get the subnet::
00010001 00001100 00001110 0010000000010001 00001100 00001110 00100000
17.12.14.3217.12.14.32

subnet mask /28 becausesubnet mask /28 because
HostHost::
00010001 00001100 00001110 0011001000010001 00001100 00001110 00110010
11111111 11111111 11111111 1111000011111111 11111111 11111111 11110000
We get the subnetWe get the subnet::
00010001 00001100 00001110 0011000000010001 00001100 00001110 00110000
17.12.14.4817.12.14.48

More Levels of HierarchyMore Levels of Hierarchy
 The structure of classless addressing does notThe structure of classless addressing does not
restrict the number of hierarchical levels.restrict the number of hierarchical levels.
 An organization can divide the granted block ofAn organization can divide the granted block of
addresses into subblocks.addresses into subblocks.
 Each subblock can in turn be divided into smallerEach subblock can in turn be divided into smaller
subblocks. And so on.subblocks. And so on.
 One example of this is seen in the ISPs.One example of this is seen in the ISPs.
 A national ISP can divide a granted large block into smallerA national ISP can divide a granted large block into smaller
blocks and assign each of them to a regional ISP.blocks and assign each of them to a regional ISP.
 A regional ISP can divide the block received from theA regional ISP can divide the block received from the
national ISP into smaller blocks and assign each one to anational ISP into smaller blocks and assign each one to a
local ISP.local ISP.
 A local ISP can divide the block received from the regionalA local ISP can divide the block received from the regional
ISP into smaller blocks and assign each one to a differentISP into smaller blocks and assign each one to a different
organization.organization.
 Finally, an organization can divide the received block andFinally, an organization can divide the received block and
make several subnets out of it.make several subnets out of it.

Address AllocationAddress Allocation
 The ultimate responsibility of address allocationThe ultimate responsibility of address allocation
is given to a global authority called the Internetis given to a global authority called the Internet
Corporation for Assigned Names and AddressesCorporation for Assigned Names and Addresses
(ICANN).(ICANN).
 However, ICANN does not normally allocateHowever, ICANN does not normally allocate
addresses to individual organizations.addresses to individual organizations.
 It assigns a large block of addresses to an ISP.It assigns a large block of addresses to an ISP.
 Each ISP, in turn, divides its assigned block intoEach ISP, in turn, divides its assigned block into
smaller subblocks and grants the subblocks tosmaller subblocks and grants the subblocks to
its customers.its customers.
 In other words, an ISP receives one large block toIn other words, an ISP receives one large block to
be distributed to its Internet users.be distributed to its Internet users.
 This is calledThis is called address aggregationaddress aggregation: many blocks: many blocks
of addresses are aggregated in one block andof addresses are aggregated in one block and
granted to one ISP.granted to one ISP.

An ISP is granted a block of addresses startingAn ISP is granted a block of addresses starting
with 190.100.0.0/16 (65,536 addresses). The ISPwith 190.100.0.0/16 (65,536 addresses). The ISP
needs to distribute these addresses to threeneeds to distribute these addresses to three
groups of customers as follows:groups of customers as follows:
a.a. The first group hasThe first group has 64 customers64 customers; each needs; each needs
256 addresses256 addresses..
b.b. The second group hasThe second group has 128 customers128 customers; each; each
needsneeds 128 addresses128 addresses..
c.c. The third group hasThe third group has 128 customers128 customers; each needs; each needs
64 addresses64 addresses..
Design the sub blocks and find out how manyDesign the sub blocks and find out how many
addresses are still available after theseaddresses are still available after these
allocations.allocations.

Solution
Figure 19.9 shows the situation.
Group 1
For this group, each customer needs 256 addresses. This
means that 8 (log2 256) bits are needed to define each
host. The prefix length is then 32 − 8 = 24. The addresses
are
Example 19.10 (contd….)Example 19.10 (contd….)

Group 2
means that 7 (log2 128) bits are needed to define each
host. The prefix length is then 32 − 7 = 25. The addresses
are

Group 3
means that 6 (log264) bits are needed to each host. The
prefix length is then 32 − 6 = 26. The addresses are
Number of granted addresses to the ISP: 65,536
Number of allocated addresses by the ISP: 40,960
Number of available addresses: 24,576

Address allocation and distribution byAddress allocation and distribution by
an ISPan ISP

(26 Mar 2014)(26 Mar 2014)
IP v6IP v6

IPv6IPv6
IPngIPng
Next-Generation IPNext-Generation IP

Why A New IP?Why A New IP?
 Inefficient usage of available IP addresses – classfulInefficient usage of available IP addresses – classful
schemescheme
 IP address depletion/exhaustionIP address depletion/exhaustion
 Aug ‘90 - Class B exhausted by Mar ‘94Aug ‘90 - Class B exhausted by Mar ‘94
 Backbone routing table growthBackbone routing table growth
 Too much data to exchangeToo much data to exchange
 Routing calculation complexityRouting calculation complexity
 Other issuesOther issues
 Security - No security mechanism (no encryption andSecurity - No security mechanism (no encryption and
authentication is provided by IPv4).authentication is provided by IPv4).
 Quality of Service - Inadequate QoS for nowadaysQuality of Service - Inadequate QoS for nowadays
application such as real-time audio and video transmissionapplication such as real-time audio and video transmission
(due to delay & resource reservation) strategy(due to delay & resource reservation) strategy

ADVANTAGE OF IPv6ADVANTAGE OF IPv6
 Larger address spaceLarger address space: IPv4 only 2: IPv4 only 23232
. IPv6 2. IPv6 2128128
340,282,366,920,938,463,463,374,607,431,768,211,340,282,366,920,938,463,463,374,607,431,768,211,
456 addresses. Can stand more than 150 years456 addresses. Can stand more than 150 years
 BetterBetter header formatheader format
 New optionsNew options: allow for additional functionalities: allow for additional functionalities
for future usefor future use
 Allowance for extensionAllowance for extension: allow the extension of: allow the extension of
the protocol if required by new technologies orthe protocol if required by new technologies or
applications.applications.
 Support for resource allocationSupport for resource allocation.- to support.- to support
traffic such as real-time audio and video verytraffic such as real-time audio and video very
very efficiently compared to IPv4.very efficiently compared to IPv4.
 Support for more securitySupport for more security. The encryption and. The encryption and
authentication options in IPv6 provideauthentication options in IPv6 provide
confidentiality and integrity of the packet.confidentiality and integrity of the packet.

Features of IPv6Features of IPv6
 Larger Address SpaceLarger Address Space
 Efficient and hierarchical addressing and routingEfficient and hierarchical addressing and routing
infrastructureinfrastructure
 efficient, hierarchical, and summarizable routingefficient, hierarchical, and summarizable routing
infrastructureinfrastructure
 Aggregation-based address hierarchy – EfficientAggregation-based address hierarchy – Efficient
backbone routing – smaller routing tablesbackbone routing – smaller routing tables
 Efficient and Extensible IP datagramEfficient and Extensible IP datagram
 Efficient Header FormatEfficient Header Format
 The IPv6 header has a new format that is designed toThe IPv6 header has a new format that is designed to
minimize header overhead.minimize header overhead.
 This is achieved by moving both nonessential fields andThis is achieved by moving both nonessential fields and
option fields to extension headers that are placed afteroption fields to extension headers that are placed after
the IPv6 header.the IPv6 header.
 The streamlined IPv6 header provides more efficientThe streamlined IPv6 header provides more efficient
processing at intermediate routers.processing at intermediate routers.

Features of IPv6Features of IPv6
 Auto-configuration - To simplify host configuration,Auto-configuration - To simplify host configuration,
 Stateless and stateful address configurationStateless and stateful address configuration
 stateful address configuration, such as address configuration in thestateful address configuration, such as address configuration in the
presence of a DHCP server - hosts on a link automatically configurepresence of a DHCP server - hosts on a link automatically configure
themselves with IPv6 addresses for the link (link-local addresses)themselves with IPv6 addresses for the link (link-local addresses)
 stateless address configuration (address configuration in the absence ofstateless address configuration (address configuration in the absence of
a DHCP server) - are derived from prefixes advertised by local routers.a DHCP server) - are derived from prefixes advertised by local routers.
 Even in the absence of a router, hosts on the same link can automaticallyEven in the absence of a router, hosts on the same link can automatically
configure themselves with link-local addresses and communicateconfigure themselves with link-local addresses and communicate
without manual configuration.without manual configuration.
 Built-in security - IPsec mandatoryBuilt-in security - IPsec mandatory
 Better support for quality of service (QoS) - New fields in the IPv6Better support for quality of service (QoS) - New fields in the IPv6
header define how traffic is handled and identified - traffic isheader define how traffic is handled and identified - traffic is
identified in the IPv6 header, support for QoS can be easily achievedidentified in the IPv6 header, support for QoS can be easily achieved
even when the packet payload is encrypted with IPSeceven when the packet payload is encrypted with IPSec
 New protocol for neighboring node interaction - The NeighborNew protocol for neighboring node interaction - The Neighbor
Discovery protocol for IPv6 - Neighbor Discovery replaces AddressDiscovery protocol for IPv6 - Neighbor Discovery replaces Address
Resolution Protocol (ARP)Resolution Protocol (ARP)
 Extensibility - IPv6 can be extended for new features by addingExtensibility - IPv6 can be extended for new features by adding
extension headers after the IPv6 header.extension headers after the IPv6 header.
 MobilityMobility

IPv6 – Improvements over IPv4IPv6 – Improvements over IPv4
 Longer addresses than IPv4Longer addresses than IPv4
 16 Bytes – 128 bits long16 Bytes – 128 bits long
 Provides unlimited supply of Internet AddressesProvides unlimited supply of Internet Addresses
 Simplification of the headerSimplification of the header
 Contains 7 fields (13 in IPv4)Contains 7 fields (13 in IPv4)
 Allows routers to process packets fasterAllows routers to process packets faster
 Improves throughput and delayImproves throughput and delay
 Better support for optionsBetter support for options
 Required because fields previously required for IPv4 are nowRequired because fields previously required for IPv4 are now
optionaloptional
 Options are represented in a different way – makes simple forOptions are represented in a different way – makes simple for
routers to skip over options not intended for them – this featurerouters to skip over options not intended for them – this feature
speeds up packet processing timespeeds up packet processing time
 Big advance in securityBig advance in security
 Authentication and privacy are key featuresAuthentication and privacy are key features
 More attention to Quality of service (QoS)More attention to Quality of service (QoS)
 AutoconfigurationAutoconfiguration

IPv6 AddressesIPv6 Addresses
128-bit long. Fixed size128-bit long. Fixed size
Larger Address space - 2Larger Address space - 2128128
= 3.4×10= 3.4×103838
addressesaddresses
⇒⇒ 665×10665×102121
addresses per sq. m of earth surfaceaddresses per sq. m of earth surface
If assigned at the rate of 10If assigned at the rate of 1066
//µµs, it would take 20s, it would take 20
yearsyears
Expected to support 8×10Expected to support 8×101717
to 2×10to 2×103333
addressesaddresses
8×108×101717
⇒⇒ 1,564 address per sq. m1,564 address per sq. m
Allows multiple interfaces per host.Allows multiple interfaces per host.
Allows multiple addresses per interfaceAllows multiple addresses per interface
Allows unicast, multicast, anycastAllows unicast, multicast, anycast
Allows provider based, site-local, link-localAllows provider based, site-local, link-local
85% of the space is unassigned85% of the space is unassigned

128 bit addresses!128 bit addresses!
 340,282,366,920,938,463,463,374,607,431340,282,366,920,938,463,463,374,607,431
,768,211,456 addresses!,768,211,456 addresses!
 Uses hierarchical addressing structureUses hierarchical addressing structure
 Allows embedding of IEEE 802 addressAllows embedding of IEEE 802 address
as EUI-64 identifiersas EUI-64 identifiers
 Specified as 8 16-bit hexadecimalSpecified as 8 16-bit hexadecimal
numbers separated by colonsnumbers separated by colons

Hexadecimal Colon NotationHexadecimal Colon Notation
 Written asWritten as eight sectionseight sections each of 2 byte length separated by colonseach of 2 byte length separated by colons
 2 bytes (16 bits) in hexadecimal requires2 bytes (16 bits) in hexadecimal requires four hexadecimal digitsfour hexadecimal digits
 Therefore address contain 32 hexadecimal digits with every four digits separated byTherefore address contain 32 hexadecimal digits with every four digits separated by
a colona colon
So, There are:So, There are:
 8 groups of 4 hexadecimal digits.8 groups of 4 hexadecimal digits.
 Each group represents 16 bits (4 hexa digits X 4 bit)Each group represents 16 bits (4 hexa digits X 4 bit)
 Separator is “:” (colon)Separator is “:” (colon)
 Hex digits are not case sensitive, so “DBCA” is same as “dbca” or “DBca”…Hex digits are not case sensitive, so “DBCA” is same as “dbca” or “DBca”…

Abbreviated IPv6 AddressesAbbreviated IPv6 Addresses
 TheThe leading zeros within a group can be omittedleading zeros within a group can be omitted – only the leading zeros can be– only the leading zeros can be
dropped, not the trailing zerosdropped, not the trailing zeros
 Further abbreviations are possible if there areFurther abbreviations are possible if there are consecutive sectionsconsecutive sections consistingconsisting
of zeros only.of zeros only.
 One or more consecutive groups of zeros can be replaced by a pair of colons –One or more consecutive groups of zeros can be replaced by a pair of colons –
allowed only once per addressallowed only once per address
 Re-expansion of the abbreviated address is very simple: Align the unabbreviatedRe-expansion of the abbreviated address is very simple: Align the unabbreviated
portions and insert zeros to get the original expanded address.portions and insert zeros to get the original expanded address.

Expand the address 0:15::1:12:1213 to its original.
Solution
We first need to align the left side of the double colon to
the left of the original pattern and the right side of the
double colon to the right of the original pattern to find
how many 0s we need to replace the double colon.
This means that the original address is.

Prefix and Interface IDPrefix and Interface ID
IPv6 (128-bit) address contains two parts:IPv6 (128-bit) address contains two parts:
 The first 64-bits is known as theThe first 64-bits is known as the prefixprefix. The prefix. The prefix
includes the network and subnet address. Becauseincludes the network and subnet address. Because
addresses are allocated based on physical location, theaddresses are allocated based on physical location, the
prefix also includes global routing information. The 64-prefix also includes global routing information. The 64-
bit prefix is often referred to as the global routingbit prefix is often referred to as the global routing
prefix.prefix.
 The last 64-bits is theThe last 64-bits is the interface IDinterface ID. This is the unique. This is the unique
address assigned to an interface.address assigned to an interface.
NoteNote: Addresses are assigned to interfaces (network: Addresses are assigned to interfaces (network
connections), not to the host. Each interface can haveconnections), not to the host. Each interface can have
more than one IPv6 address.more than one IPv6 address.

IPv6 Addressing In UseIPv6 Addressing In Use
IPv6 uses theIPv6 uses the “/” notation“/” notation to denote howto denote how
many bits in the IPv6 address representmany bits in the IPv6 address represent
the subnet.the subnet.
The full syntax of IPv6 isThe full syntax of IPv6 is
ipv6-address/prefix-lengthipv6-address/prefix-length
wherewhere
ipv6-address is the 128-bit IPv6 addressipv6-address is the 128-bit IPv6 address
/prefix-length is a decimal value/prefix-length is a decimal value
representing how many of the left mostrepresenting how many of the left most
contiguous bits of the address comprisecontiguous bits of the address comprise
the prefix.the prefix.

IPv6 Addressing In UseIPv6 Addressing In Use
Let’s analyze an example:Let’s analyze an example:
2001:C:7:ABCD::1/642001:C:7:ABCD::1/64 is reallyis really
2001:000C:0007:ABCD2001:000C:0007:ABCD::0000:0000:0000:00010000:0000:0000:0001//6464
The first 64-bitsThe first 64-bits 2001:000C:0007:ABCD2001:000C:0007:ABCD is theis the
address prefixaddress prefix
The last 64-bitsThe last 64-bits 0000:0000:0000:00010000:0000:0000:0001 is theis the
interface IDinterface ID
/64/64 is theis the prefix lengthprefix length (/64 is well-known and(/64 is well-known and
also the prefix length in most cases)also the prefix length in most cases)

Address SpaceAddress Space
IPv6 is divided intoIPv6 is divided into several categoriesseveral categories..
A few leftmost bits, called theA few leftmost bits, called the typetype
prefixprefix, in each address define its, in each address define its
category.category.
The type prefix isThe type prefix is variable in lengthvariable in length

Type Prefixes for IPv6Type Prefixes for IPv6
AddressesAddresses

IPv6IPv6
IPv6 supports 3 types of addressesIPv6 supports 3 types of addresses
 UnicastUnicast
 MulticastMulticast
 AnycastAnycast

IPv6 Address TypesIPv6 Address Types
A single interface may be assigned multiple IPv6
addresses of any type (unicast, anycast, multicast)
Address TypeAddress Type DescriptionDescription
UnicastUnicast
One to One (Global, Link local, Site local)
+ An address destined for a single interface.
MulticastMulticast
One to Many
+ An address for a set of interfaces
+ Delivered to a group of interfaces identified by that
address.
+ Replaces IPv4 “broadcast”
AnycastAnycast
One to Nearest (Allocated from Unicast)
+ Delivered to the closest interface as determined by
the IGP

(27 Mar 2014)(27 Mar 2014)
IP v6 contdIP v6 contd ……..

Unicast AddressesUnicast Addresses
Unicast addresses identify a singleUnicast addresses identify a single
interface, so defines a single computer.interface, so defines a single computer.
The packet sent to a unicast address mustThe packet sent to a unicast address must
be delivered to that specific computer.be delivered to that specific computer.
IPv6 defines two types of unicastIPv6 defines two types of unicast
addresses:addresses:
 Geographically based, andGeographically based, and
 provider-based - the provider-based address isprovider-based - the provider-based address is
generally used by a normal host as a unicastgenerally used by a normal host as a unicast
address.address.

Multicast AddressesMulticast Addresses
Multicast addresses identify a group ofMulticast addresses identify a group of
interfaces - which define a group of hostsinterfaces - which define a group of hosts
instead of just one.instead of just one.
A packet sent to a multicast address isA packet sent to a multicast address is
delivered to all of the interfaces in thedelivered to all of the interfaces in the
group – in turn delivered to each membergroup – in turn delivered to each member
of the group.of the group.
NOTE: There are no broadcast addresses inNOTE: There are no broadcast addresses in
IPv6, their function being superseded byIPv6, their function being superseded by
multicast addresses.multicast addresses.

Anycast AddressesAnycast Addresses
 IPv6 also defines anycast addresses.IPv6 also defines anycast addresses.
 Anycast addresses identify a set of interfaces such that aAnycast addresses identify a set of interfaces such that a
packet sent to a anycast address will be delivered to onepacket sent to a anycast address will be delivered to one
member of the set.member of the set.
 An anycast address, like a multicast address, alsoAn anycast address, like a multicast address, also defines adefines a
group of nodesgroup of nodes..
 However, a packet destined for an anycast address isHowever, a packet destined for an anycast address is
delivered to only one of the members of the anycast group,delivered to only one of the members of the anycast group,
thethe nearest onenearest one (the one with the shortest route).(the one with the shortest route).
 Although the definition of an anycast address is stillAlthough the definition of an anycast address is still
debatable, one possible use is to assign an anycastdebatable, one possible use is to assign an anycast
address to all routers of an ISP that covers a large logicaladdress to all routers of an ISP that covers a large logical
area in the Internet.area in the Internet.
 The routers outside the ISP deliver a packet destined forThe routers outside the ISP deliver a packet destined for
the ISP to the nearest ISP router.the ISP to the nearest ISP router.
 No block is assigned for anycast addresses.No block is assigned for anycast addresses.

Another category in the addressAnother category in the address
space is the reserved address.space is the reserved address.
These addresses start with eight OsThese addresses start with eight Os
(type prefix is 00000000).(type prefix is 00000000).
A few subcategories are furtherA few subcategories are further
defined in this categorydefined in this category

Reserved Addresses in IPv6Reserved Addresses in IPv6

Local AddressesLocal Addresses
These addresses are used when anThese addresses are used when an
organization wants to use IPv6 protocolorganization wants to use IPv6 protocol
without being connected to the globalwithout being connected to the global
Internet.Internet.
In other words, they provide addressingIn other words, they provide addressing
for private networks.for private networks.
Nobody outside the organization can sendNobody outside the organization can send
a message to the nodes using thesea message to the nodes using these
addresses.addresses.
Two types of addresses are defined forTwo types of addresses are defined for
this purposethis purpose
 Link LocalLink Local
 Site LocalSite Local

SecuritySecurity
IPv6 adds three security servicesIPv6 adds three security services
 Packet authenticationPacket authentication
 Packet integrityPacket integrity
 Packet confidentialityPacket confidentiality
Implemented using theImplemented using the
Authentication Header and theAuthentication Header and the
Encapsulating Security PayloadEncapsulating Security Payload
HeaderHeader

IPv6 HeadersIPv6 Headers
Simpler header - faster processingSimpler header - faster processing
by routers.by routers.
 No optional fields - fixed size (40 bytes)No optional fields - fixed size (40 bytes)
 No fragmentation fields.No fragmentation fields.
 No checksumNo checksum
Support for multiple headersSupport for multiple headers
 more flexible than simple “protocol”more flexible than simple “protocol”
field.field.

IPv4 HeaderIPv4 Header
VERS HL
Fragment Offset
Fragment LengthService
Datagram ID FLAG
TTL Protocol Header Checksum
Source Address
Destination Address
Options (if any)
Data
1 byte1 byte 1 byte 1 byte

IPv6 HeaderIPv6 Header
VERS PRIO
Hop Limit
Flow Label
Payload Length Next Header
1 byte1 byte 1 byte 1 byte
Source Address (128 bits - 16 bytes)
Dest. Address (128 bits - 16 bytes)

IPv6 Header FieldsIPv6 Header Fields
 VERS:VERS: IP version number – 6 (4 for IPv4)IP version number – 6 (4 for IPv4)
 Priority/Traffic Class:Priority/Traffic Class: will be used in congestionwill be used in congestion
control – to distinguish between packet withcontrol – to distinguish between packet with
different real-time delivery requirementsdifferent real-time delivery requirements
 Flow Label:Flow Label: experimental - sender can label aexperimental - sender can label a
sequence of packets as being in the same flow.sequence of packets as being in the same flow.
 Payload LengthPayload Length: number of bytes following the 40: number of bytes following the 40
byte headerbyte header
 Next Header:Next Header: tells which of the six extensiontells which of the six extension
headers follow this oneheaders follow this one
 Hop Limit:Hop Limit: same as TTL field in IPv4same as TTL field in IPv4
 Source/Destination Address:Source/Destination Address: 16 Bytes each16 Bytes each

Extension HeadersExtension Headers

Extension HeadersExtension Headers
Hop-by-Hop Option – Special options thatHop-by-Hop Option – Special options that
require hop-by-hop processingrequire hop-by-hop processing
Destination Options – Optional information toDestination Options – Optional information to
be examined by the destination nodebe examined by the destination node
Routing – Extended routing, like IPv4 loose listRouting – Extended routing, like IPv4 loose list
of routers to visitof routers to visit
Fragmentation – Fragmentation andFragmentation – Fragmentation and
reassemblyreassembly
Authentication – Integrity and authentication,Authentication – Integrity and authentication,
securitysecurity
Encrypted Security payload – ConfidentialityEncrypted Security payload – Confidentiality

IPv6 Vs IPv4 HeaderIPv6 Vs IPv4 Header
IPv6 twice the size of IPv4 headerIPv6 twice the size of IPv4 header
Version: only field with same position andVersion: only field with same position and
meaningmeaning
RemovedRemoved::
 Header length, fragmentation fieldsHeader length, fragmentation fields
(identification, flags, fragment offset),(identification, flags, fragment offset),
header checksumheader checksum
ReplacedReplaced::
 Datagram length by payload lengthDatagram length by payload length
 Protocol type by next headerProtocol type by next header
 Time to live by hop limitTime to live by hop limit
 Type of service by “class” octetType of service by “class” octet

Major Improvements of IPv6Major Improvements of IPv6
HeaderHeader
No option fieldNo option field: Replaced by: Replaced by
extension header. Result in a fixedextension header. Result in a fixed
length, 40-byte IP header.length, 40-byte IP header.
No header checksumNo header checksum: Result in fast: Result in fast
processing.processing.
No fragmentation at intermediateNo fragmentation at intermediate
nodesnodes: Result in fast IP forwarding.: Result in fast IP forwarding.

4040
bytesbytes
6060
bytesbytes
IPv4IPv4
IPv6IPv6
00 1515 1616 3131
vers IHL TOS total lengthvers IHL TOS total length
identification flags frag-offsetidentification flags frag-offset
TTL protocol header checksumTTL protocol header checksum
source addresssource address
destination addressdestination address
options and paddingoptions and padding
vers traffic class flow-labelvers traffic class flow-label
payload length next header hop limitpayload length next header hop limit
source addresssource address
destination addressdestination address
Removed (6)Removed (6)
• IHL, TOSIHL, TOS
• ID, flags, frag offsetID, flags, frag offset
• header checksumheader checksum
Changed (3)Changed (3)
Added (2)Added (2)
ExpandedExpanded
• total length => payloadtotal length => payload
• protocol => next headerprotocol => next header
• TTL => hop limitTTL => hop limit
• traffic classtraffic class
• flow labelflow label
• address 32 to 128 bitsaddress 32 to 128 bits
Header comparisonHeader comparison

IPv6 vs IPv4IPv6 vs IPv4
AddedAdded: flow label: flow label
All fields -All fields - fixed sizefixed size
No OptionalNo Optional fields. Replaced byfields. Replaced by ExtensionExtension
Headers.Headers.
 Idea:Idea: avoid unnecessary processing byavoid unnecessary processing by
intermediate routers w/o sacrificingintermediate routers w/o sacrificing thethe
flexibilityflexibility

Transition from IPv4 TO IPv6Transition from IPv4 TO IPv6
Because of the huge number ofBecause of the huge number of
systems on the Internet, thesystems on the Internet, the
transition from IPv4 to IPv6 cannottransition from IPv4 to IPv6 cannot
happen drastically.happen drastically.
Takes a large amount of time beforeTakes a large amount of time before
it will happenit will happen
The transition must be smooth toThe transition must be smooth to
prevent any problems between IPv4prevent any problems between IPv4
to IPv6 systems.to IPv6 systems.
The strategies have been devised byThe strategies have been devised by
the IETF to help the transitionthe IETF to help the transition

Three Transition StrategiesThree Transition Strategies

Dual stackDual stack
It is recommended that all hosts,It is recommended that all hosts,
before migrating completely tobefore migrating completely to
version 6, have a dual stack ofversion 6, have a dual stack of
protocols.protocols.
In other words a station must runIn other words a station must run
IPv4 and IPv6 simultaneously until allIPv4 and IPv6 simultaneously until all
the Internet uses IPv6. see fig. 20.19the Internet uses IPv6. see fig. 20.19

Dual stackDual stack

TunnelingTunneling
A strategy used when twoA strategy used when two
computers using IPv6 want tocomputers using IPv6 want to
communicate with each other andcommunicate with each other and
the packet must pass thru a regionthe packet must pass thru a region
that uses IPv4.that uses IPv4.
To pass thru this region, the packetTo pass thru this region, the packet
must have an IPv4 address.must have an IPv4 address.
So the IPv6 packet is encapsulatedSo the IPv6 packet is encapsulated
in an IPv4 packet when it enters thein an IPv4 packet when it enters the
region, and it leaves its capsuleregion, and it leaves its capsule
when exits the region.when exits the region.

Tunneling StrategyTunneling Strategy

Header TranslationHeader Translation
Header translation is necessaryHeader translation is necessary
when the majority of the internet haswhen the majority of the internet has
moved to IPv6 but some systems stillmoved to IPv6 but some systems still
use IPv4.use IPv4.
E.g. the sender wants to use IPv6,E.g. the sender wants to use IPv6,
but the receiver does not understandbut the receiver does not understand
IPv6. see fig. 20.21.IPv6. see fig. 20.21.
Tunneling doesn’t work in thisTunneling doesn’t work in this
situation bcoz the packet must be insituation bcoz the packet must be in
IPv4 format to be understood by theIPv4 format to be understood by the
receiver.receiver.

Header Translation StrategyHeader Translation Strategy

Summary – IPv6Summary – IPv6
 IPv6 uses 128-bit addressesIPv6 uses 128-bit addresses
 Allows provider-based, site-local, link-local, multicast,Allows provider-based, site-local, link-local, multicast,
anycast addressesanycast addresses
 Fixed header size. Extension headers instead ofFixed header size. Extension headers instead of
options for provider selection, security etcoptions for provider selection, security etc
 Allows auto-configurationAllows auto-configuration
 Dual-IP, 6-to-4 etcDual-IP, 6-to-4 etc for transitionfor transition

SUMMARYSUMMARY
 At the network layer, a global identificationAt the network layer, a global identification
system that uniquely identifies every host andsystem that uniquely identifies every host and
router is necessary for delivery of a packet fromrouter is necessary for delivery of a packet from
host to host.host to host.
 An IPv4 address is 32 bits long and uniquely andAn IPv4 address is 32 bits long and uniquely and
universally defines a host or router on theuniversally defines a host or router on the
Internet.Internet.
 In classful addressing, the portion of the IPIn classful addressing, the portion of the IP
address that identifies the network is called theaddress that identifies the network is called the
netid.netid.
 In classful addressing, the portion of the IPIn classful addressing, the portion of the IP
address that identifies the host or router on theaddress that identifies the host or router on the
network is called the hostid.network is called the hostid.

Network Layer Addressing in TCP/IP

Network Layer Addressing in TCP/IP

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