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The Internet, IPv4 and IPv6

ICT Technical Update Module

Post Graduate Certificate in Professional Development Slide 2

Presentation Outline• Internetworking in practice:

– How are networks interconnected?

– What devices are used?

– What is encapsulation and why is it necessary?

– How is addressing performed in the Internet?

– What is the Internet Protocol v4?

– How will the Next Generation Network use IPv6?


Objectives• You will be able to explain the various terms used for

internetworking• You will be able to explain the concepts of fragmentation

and reassembly as they apply to Internet packets• You will be able to explain why packets can be received out

of order and the mechanisms for preventing this• You will be able to perform subnet masking tasks with

Internet addresses• You will be able to identify the various special addresses

and their purposes• You will be able to compare and contrast the two versions

of the Internet Protocol.


Connecting Networks


How Networks Differ

By connect time, by packet, by byte, or not at allAccounting

Different timeouts, flow specifications, etc.Parameters

Privacy rules, encryption, etc.Security

Leaky bucket, token bucket, RED, choke packets, etc.Congestion control

Sliding window, rate control, other, or noneFlow control

Reliable, ordered, and unordered deliveryError handling

Present or absent; many different kindsQuality of service

Every network has its own maximumPacket size

Present or absent (also broadcasting)Multicasting

Flat (802) versus hierarchical (IP)Addressing

IP, IPX, SNA, ATM, MPLS, AppleTalk, etc.Protocols

Connection oriented versus connectionlessService offered

Some PossibilitiesItem


How Networks can be Connected

(a) Two Ethernets connected by a switch (b) Two Ethernets connected by a router

When to use a Hub?When you have a small network, 2 - 8 computers. Recommended with only 1 protocol, i.e. TCP/IP. Where speed is not of primeimportance, and all computers are on the same subnet.When to use a Switch?When you have a small to medium network, 5 - x computers. Recommended with only 1 protocol. Where speed is ofimportance, and all computers are on the same subnet.Where to use a Router?When you have any number of computers on different subnets. Or when you have many computers you would like to separatefrom the Public IP network. Using any number of protocols and security is of potential importance.


Internetworking• Key functions typically performed by a protocol include

– encapsulation,– fragmentation and reassembly,– connection control,– ordered delivery,– flow control,– error control,– addressing and– multiplexing

• An internet consists of multiple separate networks that areinterconnected by routers.

• Data are transmitted in packets from a source system to adestination across a path involving multiple networks androuters.

• Most widely used protocol for internetworking is theInternet Protocol (IP).

• A next generation IP, known as IPv6, has been defined.


Internetworking Terms - 1• Communications Network

– Facility that provides data transfer service

• An internet– Collection of communications networks interconnected

by bridges and/or routers

• The Internet (note the upper case I)– The global collection of thousands of individual

machines and networks

• Intranet– Corporate internet operating within the organization-

Uses Internet (TCP/IP and http) technology to deliverdocuments and


Internetworking Terms - 2• End System (ES)

– Device attached to one of the networks of an internet– Supports end-user applications or services

• Intermediate System (IS)– Device used to connect two networks– Permits communication between end systems attached to

different networks• Bridge

– Is used to connect two LANs using similar LAN protocols– Accept frames, examine the MAC addresses, and forward the

frames to different networks while doing minor protocoltranslation in the process

– OSI layer 2 (Data Link)• Router

– Connects two (possibly dissimilar) networks


Protocol Functions• Encapsulation• Fragmentation and reassembly• Connection control• Ordered delivery• Flow control• Error control• Addressing• Multiplexing• Transmission services


Encapsulation• Data, accepted or generated by entity, is usually

transferred in blocks, called Protocol Data Units(PDUs)– Each PDU contains data and control information– Some PDUs contain only control information

• Three categories of control– Address

• Of sender and/or receiver– Error-detecting code

• E.g. frame check sequence– Protocol control

• Additional information to implement protocol functions

• Addition of control information to data is referredto as encapsulation.


Fragmentation and Reassembly(Segmentation – OSI)

• To exchange data (Application level message) between twoentities, characterised as a sequence of PDUs of somebounded size, lower-level protocols may need to break dataup into smaller blocks because:– Communications network may only accept blocks of up to a

certain size• ATM 53 octets• Ethernet 1526 octets

– Error control may be more efficient with smaller PDU size• Smaller retransmission

– Fairer: more equitable access to shared transmissionfacilities, with shorter delay, can be provided, Prevent stationmonopolizing medium

– A small PDU size may mean that the receiving entities canallocate a smaller buffer.


Reassembly• Segmented data must be reassembled into

messages• More complex if PDUs are out of order….• General process is illustrated below:

Application Data PDU

Transportheader

Transportheader

Networkheader

Networkheader

Transportprotocol data units

Networkprotocol data units

(packets)


Connection Control• Connectionless data transfer

– Each PDU treated independently– E.g. datagram

• Connection-oriented data transfer– E.g. virtual circuit

• Connection-oriented preferred (even required) forlengthy exchange of data

• Three phases occur– Connection establishment– Data transfer– Connection termination– There may be interrupt and recovery phases to handle

errors


Phases of Connection - OrientedTransfer

ProtocolEntity

Connection request

Connection accept

Data

Acknowledgement

Terminate-connection request

Terminate-connection accept

ProtocolEntity

Tim

e


Ordered Delivery• PDUs may arrive out of order

– Caused by different paths through the network

• In order to maintain PDUs in order, PDUs need tobe sequentially numbered


Flow Control• Performed by receiving entity to limit the amount

or rate of data being sent• Stop and wait protocol, sliding window

techniques are both example of this approach.


Error Control• Guard against loss or damage• Error detection and retransmission

– Sender inserts error-detecting code in PDU– Receiver checks code on incoming PDU– If error, discard– If transmitter doesn't get an acknowledgment in a

reasonable time, retransmit

• Error- correction code• Error control is performed at various layers of the

protocol stack– Between station and network– Inside network


Introduction to the Internet• Interconnects tens of millions of computers

around the world and is continuing to grow veryrapidly!

• Consistently doubled in size from 1969 onwards• Started as a research project involving about 4

computers in 1969.• Users can:

– Exchange electronic mail– Read and post to electronic news bulletins– Access files on remote computers anywhere in the

world– Publish information to other Internet users


The Internet

• Collection of networks organised into a multi-level hierarchy• Independent of hardware type.• At the lowest level of this hierarchy, we have up to about 100 computers

connected to each other and to a router using a local area network.• Routers at the lowest level are typically connected to routers in a local

area or campus-wide network.• At the next level, the routers in the campus network are connected to

routers belonging to an Internet Service Provider (ISP).• These routers are finally connected to a high-speed wide area network

that is called a backbone network.


3 Concepts Underpinning the Internet• The key concepts that underpin the Internet are:

– Addressing• People need to be able to send data to you through the

network. This requires a method for identifying you as theintended recipient! Hence the need to have an addresswhere you can be reached.

– Routing• There needs to be a methodology to send messages

around the network based on prevailing networkconditions, speeds of the links, availability of capacity etc.

– Internet Protocol• All the devices in the network need to speak the same

“language” and this is a protocol for ensuring that themessages can be delivered correctly to their intendedaddressee.

Note:Note: Each of these concepts is designed to be scalable to largenetworks


Internet Technology

• Two principal ideas support Internettechnology:

– Packets– Store and forward transmission

InformationInformation

PacketsPackets

Illustration of the Store and Forward technique:

Packetising of a message:

StartStart EndEnd


Packets

• Packet consists of– Header (meta-data)– Payload

• Header consists of– Source and destination addresses– Data length information– Sequence numbers– Type of data stored in the payload

• Payload– User information

Payload Header


Problems with Packets• Packets are quite efficient as a means of transferring

data, but applications such as voice or other real-timeservices may experience some problems.

• Consider digitising voice at the rate of 8000 samplesper second. Suppose that each sample is just 1 byte.– How long will it take to fill a 500-byte packet?– If interactive voice can only tolerate 100msec of delay,

what fraction of the 100msec is actually spent onpacketisation?

•• Answers:Answers:– Each sample corresponds to 1/8000 seconds so 500

samples take 500/8000 = 62.5msec.– As a fraction of 100msec we can see that 62.5% of the

delay budget is taken up with packetising the voice!!!


Store and Forward Operation• Store and forward operation is used in both

message and packet switching:

Message SwitchingA

BC

D

Message is first passed to B in its entirety and then it ispassed to C in its entirety and finally to node D.

Packet SwitchingA

BC

D

As for the messageswitching case but inpackets.


Problems with Store and ForwardOperation

• Store and forward networks are less expensive to operatethan circuit switched networks, but users do find someproblems with store and forward operation:

– Users cannot control how long their packets will take totraverse the network - how long will packets be delayed?

– By definition, packets are stored at the network nodes. Bufferspace can be expensive.

– Buffers are finite in size and so there is a chance that it will beinsufficient if many users send data via the same node -leading to loss of packets if the buffer is full. Controls may beneeded to ensure that packets won’t be dropped.

Packet arrivals Buffer SpaceServer


3 Concepts Underpinning the Internet(Revision)

• The key concepts that underpin the Internet are:– Addressing

• People need to be able to send data to you through the network.This requires a method for identifying you as the intendedrecipient! Hence the need to have an address where you can bereached.

– Routing• There needs to be a methodology to send messages around the

network based on prevailing network conditions, speeds of thelinks, availability of capacity etc.


“language” and this is a protocol for ensuring that the messagescan be delivered correctly to their intended addressee.

• The key concepts that underpin the Internet are:– Addressing

• People need to be able to send data to you through the network.This requires a method for identifying you as the intendedrecipient! Hence the need to have an address where you can bereached.

– Routing• There needs to be a methodology to send messages around the

network based on prevailing network conditions, speeds of thelinks, availability of capacity etc.


“language” and this is a protocol for ensuring that the messagescan be delivered correctly to their intended addressee.

Note:Note: Each of these concepts is designed to be scalable to large networks


Addressing - 1

• An Internet Protocol address (“IP address”) corresponds to a host-interface card - ie a device that connects a computer to a network.

• If a computer has more than one interface card it will require more thanone IP address.

• IP addresses are set up in a two-part hierarchy:– Network number– Interface number (also called a host number)

• Both the network and interface numbers are unique so that we canuniquely identify the device/card that is connected to the network.


Addressing - 2• A central authority allocates a network operator with a

unique network number range.• Once this number has been assigned, the operator can

allocate a globally unique IP address with the prefix andthis allows decentralised control of the address space.

• If addresses had not been based on this hierarchicalstructure, we would require a central authority to checkevery IP address for uniqueness!!!

Network Number102.54.94

Interface number97

rhino.acme.com


Address Classes - 1

• An important aspect of addressing is to work out how toallocate bits to the network and interface numbers.

• If the Internet had many networks but few interfaces then itwould be better to allocate more bits to the network address. Ifthe opposite case prevailed, then we would obviously reversethe situation.

• In IP Version 4, the addresses are 3232 bits in length:– If we use 24 bits for the address of the network number and the

remaining 8 bits for the interface number then we could have 224

networks (16,772,216) and 28 = 256 interfaces per network.– A total of 4,294,967,296 computer cards/interfaces are possible!


Address Classes - 2

• Internet designers initially thought there would only be 256networks so the situation described would have beenreversed!

• In fact, a rather more flexible scheme was adopted, viz:– Partition the address space into Class A, Class B, Class C and

Class D addresses with different numbers of bits assigned tothe network and interface numbers in each class.

– A Class A address has 8 bits for the network number and 24bits for the interface number.

– A single large part of the Internet would use a Class Aaddress.

– But by contrast, a Class C address has 24 bits of networknumber and only 8 bits of interface number. This means thatonly 256 hosts can be accommodated in a Class C network.


Address Classes - 3

• The network can distinguishbetween the 4 classes of addressby the first few bits of the networknumber:

– Class A - first bit is ‘0’– Class B - first two bits are ‘10’– Class C - first three bits are ‘110’– Class D - first four bits are ‘1110’– Class E - first four bits are ‘1111’

• Used for experimental purposesonly.

• Using these bits from the network number has the effect of reducing the overallnumber of networks in each of the classes.

• Class A networks are only 7 bits long so there can only be 128 large class networks.• Class B networks consists of 14 bits so there can only be 16,384 medium class

networks.

0

0

01

1

Class A

Class B

Class C

Class D

1

0

Class E

1


Address Classes - 4• As mentioned above, there are 5 classes of

address format in the Internet.• The following table shows the allocations of bits

for these classes:

High order bits010

11011101111

Format7 bits net, 24 bits host14 bits net, 16 bits host21 bits net, 8 bits host28 bits multicast group #reserved for experiments

ClassABCDE


Exercise

• Compute the number of Class C networkspossible.

• Hint: A class C address consists of 21 bits for thenetwork number and 8 bits for the interfacenumber. Refer to previous slide…..

•• Your Answer:Your Answer:


Address Class Problems - 1

• We have stated that IP Version 4 addresses are 32 bits long andcan theoretically address a total of 4,294,967,296 computercards/interfaces.

• In practice, we find that after the central authority hands out theaddress space allocations, there is little control that can beexercised over how much of that space is used. In earlier times,Class A and B spaces were rather freely allocated and rathersparsely used and cannot be reclaimed.

• To solve this problem, IP Version 6 - or IPng has been proposed- this will be discussed at another time.


Address Class Problems - 2

• If a campus network had more than 256 nodes, it would need aClass B address. This provides 65,536 nodes in the address space,but this is a very large number and typically the campus networkwould not have this many hosts.– Thus, there is considerable wastage if we adopt this approach.

• A solution is to use Classless Inter Domain Routing addresses(CIDR).– In this form of addressing, the network number can be an arbitrary

number of bits long so that the size of the network can be bounded bysome power of 2.


Internet Addresses - 2• Addresses are usually represented as four

decimal numbers separated using dots.• Each number represents an octet of the address.

– For example, consider 10.0.0.1– The binary representations are

• 00001010 00000000 00000000 00000001

High order bits0

10110

11101111

Format7 bits net, 24 bits host14 bits net, 16 bits host21 bits net, 8 bits host28 bits multicast group #reserved for experiments

ClassABCDE


Internet Addresses - 3• The two level hierarchy (network and host

numbers) were initially thought to be sufficient,but by 1984, it became clear that a thirdhierarchical level was needed and so the“subnet” was added to the hierarchy at that time.

• This leads to the following format:

Network number Subnet Host


Internet Addresses - 4• Consider a general B-class address as shown below.

By using a more flexible arrangement when we wantmore than 256 but fewer than 65,536 hosts, we couldflexibly rearrange the address like this:




More subnets and fewer hosts

Fewer subnets and more hosts

This flexibility is enabled using a device known as a subnet mask


Internet Addresses - 5• Here are some example B-class network options:

Network number 14 bits 2 bits



16,384 subnets 4 hosts




64 subnets 1,024 hosts

10

10

10

10

……………………………………………………


Internet Addresses - 6

• The subnet field can have any length - it isspecified by a 32-bit “mask”.

• You find an address belongs to a subnet bycomparison using a mask operation:– This means that all bits of the address for which

the corresponding mask bit is null are zeroedand the result compared to the subnet identifier.

Mask Address Net Subnet Host

0xFFFF00000xFFFFFE00

0xFFFFFFC0

10.27.32.100136.27.33.100136.27.34.141193.27.32.197

A: 10 27 32.100B: 136.27 16 (32) 1.100

136.27 17 (34) 0.141C: 193.27.32 3 (192) 5


Internet Addresses - 7• Here are three examples of the masks given on the

previous slide in their Hex, Binary and “Dot” formats:

FFFF0000

1111 1111 1111 1111 0000 0000 0000 0000

255 . 255 . 0 . 0

Hex Format

Binary Format

Dot Format

FFFFFE00

255 . 255 . 254 . 0

1111 1111 1111 1111 1111 1110 0000 0000

Hex Format

Binary Format

Dot Format

FFFFFFC0

255 . 255 . 255 . 192

1111 1111 1111 1111 1111 1111 1100 0000

Hex Format

Binary Format

Dot Format


Exercise• Use the masks shown on the previous slide to

show the Net/Subnet/Host results on the righthand side of the table are correct.

•• Answer:Answer:


Answers - 1• First we convert the address into binary form:

10.27.32.100

0000 1010 0001 1001 0010 0000 0110 0100 Then we add the mask in binary form:

1111 1111 1111 1111 0000 0000 0000 0000 (Mask)

0000 1010 0001 1001 0000 0000 0000 0000 Then we perform the masking:

A-class address!

Result:

Net: 10 Subnet: 27 Comparison

Host: 32.100

We note that the length of the subnet mask here was the samelength as the length of a normal A-class address in this case.

We note that the length of the subnet mask here was the samelength as the length of a normal A-class address in this case.


Answers - 2 First we convert the address into binary form:

136.27.33.100


1111 1111 1111 1111 1111 1110 0000 0000 (Mask: FFFFFE00)


B-class address!

Result:

Net: 136.27 Comparison

Host: 1.100Subnet: 16

Normal B-class address specification: 10 + 14 bit net address + 16 bits for hostsArrangement illustrated above:

10 + 14 bit net address + 7 bit subnet address + 9 bit host addressLeads to 128 subnet addresses and 512 hosts per subnet possible.





136.27.34.141


1111 1111 1111 1111 1111 1110 0000 0000 (Mask: FFFFFE00)


B-class address!

Result:

Net: 136.27 Comparison

Host: 0.141Subnet: 17







193.27.32.197


1111 1111 1111 1111 1111 1111 1100 0000 (Mask: FFFFFFC0)


C-class address!

Result:

Net: 193.27.32 Comparison

Host: 5Subnet: 3

Normal C-class address specification: 110 + 21 bit net address + 8 bits for hostsArrangement illustrated above:


Normal C-class address specification: 110 + 21 bit net address + 8 bits for hostsArrangement illustrated above:



One more for you to try!

130.50.15.6

1000 0010 0011 0010 0000 1111 0000 0110

1111 1111 1111 1111 1111 1100 0000 0000 (Mask: FFFFFC00)

?-class address?

You do the rest!You do the rest!


Special Purpose Addresses - 1• It can be the case that a host does not know its IP

address or the IP address of its neighbour - forexample when the host boots up.

• Several addresses have been established forhandling this type of situation

• When the network number is unknown, a hostcan use ‘0’ as a substitute.

• The special address 0.0.0.0 means “the host onthis network”.– The special address can only be used as a source

address - eg when the host is booting– An address of 0.X.Y.Z means the host X.Y.Z on this

network.


Special Purpose Addresses - 2

• The special address 255.255.255.255 isknown as the limited broadcast address– This address can only be used as a destination

address• Send a packet to all the hosts on the local subnet.• Packets cannot be relayed to any other network

outside of the local one.

• The special addresses A.255.255.255 orB.B.255.255 or C.C.C.255 are referred to asdirected broadcast message addresses.– Packets sent to these addresses are intended to

reach all hosts within the Class A, B or Cnetworks respectively.


Special Purpose Addresses - 3

• A consequence of this special purpose addressing is thatno subnet is allowed to have a null number, or a numberthat is expressed entirely in binary ones.– If we use 3 bits for the subnet number, for example, then we

can use only the values from 1 - 6.– In addition, we cannot have a subnet with a number that is

only one bit long!!!

• In addition to the above special addresses, Internetnumbering authorities have reserved other special“multicast” addresses as well.


Special Purpose Addresses - 4• Multicast addresses

– 224.0.0.1 = All systems on this subnet– 224.0.0.2 = All routers on this subnet

• Examples

Some unknown host (source)Any host (destination)Host 3 in Class B network 129.34Some host in network 129.34 (source)Any host in 129.34 (destination)Host number 3 on this network (source)This host (local loop)

Addresses Description

0.0.0.0255.255.255.255129.34.0.3129.34.0.0129.34.255.2550.0.0.3127.0.0.1


Internet Protocol - Introduction• The Internet Protocol will now be presented in

more detail.• The components of interest are:

– Formats– Procedures

• Service types• Fragmentation• Reassembly• Options


Internet Header - 1

012345678901234567890123456789011 2 3

Version IHL Type of service Total Length

Identification

Protocol

Flags

Header Checksum

Source Address

Destination Address

PaddingOptions

Fragment Offset

Time to live

• The following diagram shows the Internet Headerdetails:


Internet Header - 2• The header must carry source and destination information,

parameters for use by the routers in the network and optiondetails.

• We review the first 32 bits of the header below:

IHL Type of service Total LengthVersion

Version: Currently is version ‘4’

IHL: Internet header length, expressed in 32-bit words(Varies from 5 to 15 depending on options present)

Type of Service: Packet’s precedence and desired routing.

Total Length: Number of octets contained in the packet(including the packet header). As this field is 16 bits longthis limits the packet size to 65,535 octets.


Internet Header - 3• The identification, flags and fragment offset will

be considered in more detail a little later.• The second 32 bit section is presented below:

Identification Flags Fragment Offset


Internet Header - 4• The third 32 bit word of the header:

Time to live Protocol Header Checksum

Time to live: This was supposed to be measured in seconds andrepresented the maximum lifetime in the network.Decremented by one after passing through a router. Ifzero, the packet should be destroyed. More detail later.

Protocol: When the packet reaches its destination, this field isused to determine which program should be passedthe packet. (See later for possible programs.)

Header Checksum:This is computed as the 16-bit one’s complement sumof all 16-bit words in the header after zeroing thechecksum field itself.


Internet Header - 5• The fourth and fifth 32 bit words from the header

are the source and destination addresses

Source Address

Destination Address


Internet Header - 6• The Sixth 32 bit word from the header

Options Padding

Options: This field was defined for the specific purpose of requestingparticular routing for some packets. A packet can carry severaloptional parameters - all concatenated together.

Padding: This field simply contains “No Op” fields to follow the optionsinformation where required.


Protocol Numbers• As mentioned above, the protocol field is used to identify the

program to run when the packet is received at the destination.• The following table lists some of these programs:

01234568

172938808889

255

ProtocolKeywordDecimal

ICMPIGMPGGPIPSTTCPEGPUDPISO-TP4IDPR-CMTPISO-IPIGRPOSPF

ReservedInternet Control MessageInternet Group ManagementGateway to GatewayIP in IP (encapsulation)StreamTransmission ControlExterior Gateway ProtocolUser DatagramISO-Transport Protocol Class 4IDPR-Control Messager Transport ProtocolISO- Internet Protocol (CLNP)IGRPOpen Shortest Path FirstReserved


Precedence and Type of ServiceField

• The type of service field actually carries two sub-fields– Precedence

• An indication of priority

– Type of service• An indication for routing

Precedence Type of service

D T R C

0 1 2 3 4 5 6 7

D - Delay; T - Throughput; R - Reliability; C - Cost


Precedence• The precedence indicator affects queueing.• If several packets are awaiting transmission on

the same channel, the one with the highestprecedence is supposed to be sent first.

• There are eight preference values, viz:

111 - Network Control110 - Inter-network Control101 - CRITIC-ECP100 - Flash Override011 - Flash010 - Immediate001 - Priority000 - Routine


Type of Service• Often there is more than one route to a

destination. These routes may have quitedifferent characteristics. Eg telephone circuits,satellite links, radio channels,…

• We want to indicate to the routing protocols howwe would like the packet to be routed.

• As indicated above, the four types of service areD, T, R and C:

– D - Delay: This is a mechanism for requesting low delays (avoidsatellite links)

– T - Throughput: Select path with highest throughput (avoid telephonelinks)

– R - Reliability: Highest reliability (avoid radio channels)– C - Cost: Cheapest route


Fragmentation and Reassembly - 1

• Internetworking programs need to pass packets from one networkto another.

• Sometimes this means that the packets are the wrong size andthey would be rejected or broken into more manageable pieces.

• The sizes used may be related to the maximum size but it is morecommon to have them related to the data rate of the network or tothe expected/known error rate.

• The IP Header contains specific fields to manage thefragmentation and reassembly process involved in interworkingbetween networks.


Identification Flags Fragment Offset

Network


Fragmentation and Reassembly - 2

• The flags field has three bits.• The first bit is reserved for future use and must

be set to zero.• The DF bit means don’t fragment. If this bit is set,

then the router should discard the packet if it istoo large. (An ICMP error message needs to bereturned to the source address - if possible.)

• The MF bit means more fragments to follow.

Flags0

DF

MF

0 1 2


Options and Header Processing• Options are not used very often in modern

internets and intranets– There is an overhead penalty in processing these

options in the header.– Alternative approaches have been found - particularly

for high speed networks.

Where to now?IP Version 6/IPng

The future of the Internet Protocol

Professor Richard Harris

Presentation Outline• IP Version 6 Background/History• IPv6 Overview• New Header format• Extension Headers and Options• Quality of Service• Security• ICMP Version 6• Migration Issues


Objectives• You will be able to discuss the reasons for the

new generation Internet Protocol• You will be able to describe the new header

format and the extended capabilities of theprotocol that result from these changes.

• You will understand the need for QoS and QoSparameters

• You will have an appreciation of the issuesinvolved in migrating from the current version ofIP (v4) to the new version IPng.


History - 1• The Internet Protocol was introduced in the ARPANET in the mid-

1970s.• The version of IP in common use today is IP version 4 (IPv4),

described in Request for Comments (RFC) 791 (September 1981).• IPv4 was never intended for the Internet that we have today, either

in terms of the number of hosts, types of applications, or securityconcerns.

• In the early 1990s, the Internet Engineering Task Force (IETF)recognised that the only way to cope with these changes was todesign a new version of IP to become the successor to IPv4.

• The IETF formed the IP next generation (IPng) Working Group todefine this transitional protocol to ensure long-term compatibilitybetween the current and new IP versions, and support for currentand emerging IP-based applications.

• Work started on IPng in 1991 and several IPng proposals weresubsequently drafted.


History - 2• The result of this effort was IP version 6 (IPv6),

described in RFCs 1883-1886.• These four RFCs were officially listed in

December 1995.• IPv6 is designed as an evolution from IPv4 rather

than as a radical change.• Useful features of IPv4 were carried over in IPv6

and less useful features were dropped.


IP Version 6 Overview• The key changes from IPv4 to IPv6 can be

summarised as:– Expanded addressing range– Simplified header format– More support for extensions and options– Quality of service capabilities using “flow labelling”.– Extensions to support authentication and privacy issues


‘New’ Terminology in IPv6• There have been improvements made to terminology to

make things clearer! Here are some examples:• Packet: An IPv6 protocol data unit (PDU), comprising a header

and the associated payload. In IPv4, this would have beentermed packet or datagram.

• Node: A device that implements IPv6.• Router: An IPv6 node that forwards packets, based on the IP

address, not explicitly addressed to itself. In former TCP/IPterminology, this device was often referred to as a gateway.

• Host: Any node that is not a router; these are typically end-usersystems.

• Link: A medium over which nodes communicate with each otherat the Data Link Layer (such as an ATM, frame relay, SMDS widearea network, an Ethernet or token ring LAN).

• Neighbours: Nodes attached to the same link.


Addressing• Expanded Addressing Capabilities:

– The IP address size is increased from 32 bits to 128 bitsin IPv6, supporting a much greater number ofaddressable nodes, more levels of addressinghierarchy, and simpler auto configuration of addressesfor remote users.

– The scalability of multicast routing is improved byadding a Scope field to multicast addresses.

– A new type of address, called anycast, is also defined.

• According to some sources, 2128 is greater thanthe number of molecules that are present in theuniverse!


New IPng Header Format• Header Format Simplification: Some IPv4 header fields

have been dropped or made optional to reduce packetprocessing and to limit the bandwidth cost of the IPv6header.

• Note that although IPv6 addresses are four times the size ofIPv4 addresses, the basic IPv6 header is only twice the sizeof an IPv4 header, thus decreasing the impact of the largeraddress fields.

• The old and new header formats are shown in the next fewslides.


Old IP Version 4 Header

012345678901234567890123456789011 2 3


Identification

Protocol

Flags

Header Checksum

Source Address

Destination Address

PaddingOptions

Fragment Offset

Time to live

This is the old header format used in Version 4.


The New Header Format

012345678901234567890123456789011 2 3

Version Priority Flow Label

Payload Length Next Header

Source Address - 1

Destination Address - 4

Hop Limit

Source Address - 2

Source Address - 3

Source Address - 4




IPv6 Header Format (from RFC 1883)


Flow Label

Header Content - 1• The first 32 bits of the new header:

• Version: IP version number (4 bits). This field's size is 6 forIPv6 (and 4 for IPv4). Note that this field is in the samelocation as the Version field in the IPv4 header, making itsimple for an IP node to quickly distinguish an IPv4 packetfrom an IPv6 packet.

• Priority: Enables a source to identify the desired deliverypriority of this packet (4 bits).

• Flow Label: Used by a source to identify associatedpackets needing the same type of special handling, suchas a real-time service between a pair of hosts (24 bits).

Version Priority


Header Content - 2

• Second 32 bits of the new header:– Payload Length: Length of the payload (the portion of the packet following the

header), in octets (16 bits).• The maximum value in this field is 65,535; if this field contains zero, it means that the

packet contains a payload larger than 64KB and the actual payload length value iscarried in a Jumbo Payload hop-by-hop option.

– Next Header: Identifies the type of header immediately following the IPv6header; uses the same values as the IPv4 Protocol field, where applicable (8bits).

• The Next Header field can indicate an options header, higher layer protocol, or noprotocol above IP.

– Hop Limit: Specifies the maximum number of hops that a packet may takebefore it is discarded (8 bits).

• This value is set by the source and decremented by 1 by each node that forwards thepacket; the packet is discarded if the Hop Limit reaches zero. The comparable field inIPv4 is the Time to Live (TTL) field; it was renamed for IPv6 because the value limitsthe number of hops, not the amount of time that a packet can stay in the network.

Payload Length Next Header Hop Limit


Header Content - 3• Address Fields:

Source Address: IPv6 address of the originator of the packet(128 bits).

Destination Address: IPv6 address of the intended recipient(s)of the packet (128 bits).

Source Address - 1


Source Address - 2

Source Address - 3

Source Address - 4





Extension Headers and Options• Improved Support for Extensions and Options:

– IPv6 header options are encoded in such a way to allowfor more efficient forwarding, less stringent limits on thelength of options, and greater flexibility for introducingnew options in the future.

– Some fields of an IPv4 header have been made optionalin IPv6.


Values for the Next Header Field

Value Contents of the next header1 Internet Control Message Protocol (ICMP)6 Transmission Control Protocol (TCP)17 User Datagram Protocol (UDP)43 Routing header44 Fragment header58 Internet Control Message Protocol version 6 (ICMPv6)59 Nothing; this is the final header60 Destination Options header89 Open Shortest Path First (OSPF)

This table gives possible values for the next headerfield:


Quality of Service - 1

• Flow Labelling Capability:– A new quality-of-service (QOS) capability has been added to enable the labelling

of packets belonging to particular traffic “flows” for which the sender requestsspecial handling, such as a real-time service.

– It should be noted that the concept of a flow in IP is a major departure from IPv4and most other connectionless protocols.

– Special handling for non-default quality-of-service is an important capability inorder to support applications that require guaranteed throughput, end-to-enddelay, and/or jitter, such as multimedia or real-time communication. These QOSparameters are an extension of IPv4's Type of Service (TOS) capability.

– The Priority field allows the source to identify the desired priority of a packet.Values 0–7 are used for congestion-controlled traffic, or traffic that backs off inresponse to network congestion, such as TCP segments.


Quality of Service - 2

Uncharacterised traffic“Filler” traffic (eg. Netnews)Unattended data transfer (eg. e-mail)(reserved)Attended bulk transfer (eg. FTP, HTTP, NFS)(reserved)Interactive traffic (eg. Telnet, X)Internet control traffic (eg. routing protocols, SNMP)

Priority Description

01234567

The following table lists the priority values thatare recommended for congestion-controlled traffic:

For non-congestion controlled traffic, the values of priority start at ‘8’ for packetsthat could be discarded up to priority ‘15’ that are least willing to be discarded.

For non-congestion controlled traffic, the values of priority start at ‘8’ for packetsthat could be discarded up to priority ‘15’ that are least willing to be discarded.


Security• Authentication and Privacy Capabilities:

– Extensions to support security options, such asauthentication, data integrity, and data confidentiality,are built-in to IPv6.

• IP Version 4 had very few, if any security featuresand this has become a problem in recent years.

• IP Version 6 has two special security features:(see RFC 1826 and RFC 1827 for details)– The IP Authentication Header– The IP Encapsulating Security Payload (ESP)

• These features should add to the overall securityof the new protocol.


ICMP Version 6 - 1• As previously discussed, the Internet Control

Message Protocol (ICMP) provides error andinformation messages that are beyond thecapabilities of IP to provide.

• ICMP for IPv6 (ICMPv6) is functionally similar toICMP for IPv4 and uses a similar message format,and forms an important and integral part of IPv6.

• ICMPv6 messages are carried in an IPv6datagram with a Next Header field value of 58.


ICMP Version 6 - 2• ICMPv6 error messages are:

• Destination Unreachable: Sent when a packet cannot bedelivered to its destination address for reasons other thancongestion

• Packet Too Big: Sent by a router when it has a packet thatit cannot forward because the packet is larger than theMTU of the outgoing link

• Time Exceeded: Sent by a router that when the packet'sHop Limit reaches zero or if all fragments of a datagramare not received within the fragment reassembly time

• Parameter Problem: Sent by a node that finds someproblem in a field in the packet header that results in aninability to process the header).


Migration Issues

• Before IPv6 can be widely deployed, the networkinfrastructure must be upgraded to employ software thataccommodates the new protocol.

• In addition, the new address format must be accommodatedby every TCP/IP protocol that uses addresses.

– The Domain Name System (DNS), for example, has defined anAAAA resource record for IPv6 128-bit addresses (IPv4's 32-bitaddresses use an A record) and the IP6.INT address domain(IPv4 uses the ARPA address domain).

– Other protocols that must be modified for IPv6 include DHCP,the Address Resolution Protocol (ARP) family, and IP routingprotocols such as the Routing Information Protocol (RIP), OpenShortest Path First (OSPF) protocol, and the Border GatewayProtocol (BGP). Only after the routers and the backbones areupgraded will hosts start to transition to the new protocol andapplications be modified to take advantage of IPv6'scapabilities.


IPv4 and IPv6 Co-existence

• The above diagram shows a possible scenario forfuture co-existence in the transition period.

IPv4Network

IPv6Network IPv4/IPv6

RouterIPv4/IPv6

Router

IPv6Network

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