Guide to TCP/IP, Third Edition

Chapter 13: Internet Protocol Version 6

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Objectives

• Understand the limitations of IPv4 and how the creation of IPv6 helps to overcome them

• Understand the structure and capabilities of the new IPv6 address space

• Consider how routing is affected under IPv6

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Objectives (continued)

• Understand IPv6 packet formats

• Discuss new and enhanced IPv6 features

• Understand how IPv6 and IPv4 coexist, and how to use both versions simultaneously

• Understand impediments involved in transitioning from IPv4 to IPv6

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Why Create a New Version of IP?

• IPv4 address space– Recognizes only four billion unique IP addresses in

round numbers

• Usable address space– Number of hosts that could actually be connected to

the Internet

• Most critical shortcoming of IPv4 – Lack of universally valid IP addresses

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The IPv6 Address Space

• IPv6 solves address shortage problem by – Creating address space that is more than 20 orders

of magnitude larger than IPv4’s address space

• IPv6 address space – Provides hierarchy in a flexible and well-articulated

fashion with room for future growth

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Address Format and Allocations

• IPv6 address – 128 bits long– String that uniquely identifies one single network

interface on the global Internet

• If entity is on the same subnet as the host– Both share a large part of that address

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Address Format and Allocations (continued)

• Scope identifier– Four-bit field that limits the valid range for a multicast

address

• IPv6– Requires each single interface within each device to

have its own unique interface identifier– Specifies that interface identifiers follow the Modified

EUI-64 format

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Address Format and Allocations (continued)

• IPv4-compatible address and the IPv4-mapped address– IETF defined type IPv6 addresses that contain IPv4

addresses within them

• RFC 2732– Describes a method to express IPv6 addresses in a

form compatible with HTTP URLs

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Address Types

• Unspecified address – All zeroes and can be represented as two colon

characters (::) in normal notation

• No broadcast address in IPv6

• Multicast addresses in IPv6– Used to send an identical message to multiple hosts

• Solicited node address– Used to support Neighbor Solicitation (NS)

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Address Types (continued)

• Anycast address – Used to address functions commonly deployed on

the Internet at multiple network locations

• Unicast address– Sent to one network interface

• Aggregatable global unicast address– Can be combined with other addresses into a single

entry in the router table

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Address Types (continued)

• Link-local address – Has its first 10 (leftmost) bits set to 1111111010

• Site-local address– Has its first 10 (leftmost) bits set to 1111111011

• IPv6– Pre-allocates only about 15% of its available

addresses– Address space set aside for addresses using

Network Service Access Point (NSAP) type addressing

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Routing Considerations

• IPv6 – Designed from the ground up with routing efficiency

and throughput in mind– Designed to reduce the workload of Internet routers– Allocation schemes attempt to build in as much

aggregatability as possible without “tyrannizing” users

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Neighbor Discovery and Router Advertisement

• ND uses five ICMP message types– Router Solicitation (RS)– RouterAdvertisement (RA)– Neighbor Solicitation (NS)– Neighbor Advertisement (NA)– Redirect

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Path MTU Discovery and Changes in Fragmentation

• Senders are required to – Check the Path MTU (PMTU) between themselves

and the destination before they send– Size packets accordingly

• Every network segment or link has its own MTU

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Working with IPv6 Protocols

• Mechanisms that IPv6 uses to handle name resolution

• Native packet formats and field layouts used in IPv6

• Mechanisms used to support automatic address assignment or allocation

• Security enhancements

• Manage service levels and priorities for different types of traffic

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Nam Resolution in IPv6

• Domain Name System (DNS) – Continues to operate in IPv6 environments where it

is known as DNSv6

• What IPv6 offers that IPv4 does not– Backup service that can stand in for DNS

• Link Local Multicast Name Resolution (LLMNR) protocol – Uses same message format that conventional DNS

also uses, but runs on different ports

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IPv6 Packet Formats

• IPv6 packets – Consist of a fixed, constant format 40-byte header,

optional extension headers, and the payload (data) • All encapsulated within a Data Link layer frame

• IPv6 header – Designed to reduce processing time at the

destination and on intervening routers

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Basic IPv6 Header Format

• IPv6 header format differs from IPv4 packet structure in the following ways– Six IPv4 header fields were removed

• Internet Header Length, Type of Service

• Identification, Flags, Fragment Offset

• Header Checksum

– Three IPv4 fields were renamed or altered• Total Length, Protocol, and Time to Live

– Two new fields were added• Class and Flow Label

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Extension Headers

• Recommended order for the extension headers– 1. Hop-by-Hop Options– 2. Destination Options– 3. Routing– 4. Fragment– 5. Authentication– 6. Encapsulating Security Payload (ESP)– 7. Destination Options

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New and Enhanced IPv6 Features

• Autoconfiguration – Allows host to find the information it needs to set up

its own IP networking parameters

• DHCP – Common autoconfiguration tool deployed across

many parts of the Internet today

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Autoconfiguration

• Three things combine to make autoconfiguration important for the Internet– The sheer number of nodes to be configured– The rate of change and the frequency of

renumbering– User mobility

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Stateless Autoconfiguration

• RFC 2462 – Proposes tools to support stateless

autoconfiguration of attached nodes

• Stateless autoconfiguration – Can be used alone or in conjunction with a stateful

autoconfiguration method, such as DHCPv6

• Routers on the local link – Can be configured to provide pointers to DHCPv6

servers

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Security

• May mean – The ability to detect alterations made to a

communication after some point in time– The ability to check the credentials of a user to keep

or share a secret

• Biggest change from IPv4 to IPv6 – Security, in the form of IPSec, is a required part of

IPv6

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Terms of Encryption

• Computer security– Based on sets of mathematical manipulations called

transformations

• Encryption – Used to keep communications secret or private

• Ciphertext– Scrambled document

• Compression – Attempts to find patterns in the plain text and

express those patterns in fewer characters

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Quality of Service

• The ability of a network to provide better service to specific types of network traffic

• Handled by the diffserv working group at the IETF

• Resource Reservation Protocol (RSVP) – Early attempt to promote a more formal approach to

dynamic resource allocation on the Internet

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Router Alerts and Hop-by-Hop Options

• IPv6 header – Eliminates all the fields relating to QoS

• RFC 2711 – Defines the router alert option in the Hop-by-Hop

Options extension header

• Router alert option– Tells intervening routers to examine the packet more

closely for important information

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Mobile Users

• Micro-mobility– Generally dealt with at the link layer, below IP – Maintains connectivity to a local link over a wireless

connection

• Ordinary mobility– Takes place on a slightly larger scale, such as

logging onto a network in Copenhagen

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Coexistence of IPv4 and IPv6

• Dual stack – Implementations for individuals or small offices may

work as experiments, but• Are limited by the availability of dual stack routers at

ISPs at the edge of the Internet

• Most important dual stack machines – Will be the routers themselves

• Dual stack router– Can provide a connection between the IPv4 Internet

and an office that already made the switch to IPv6

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Tunneling Through the IPv4 Cloud

• Internet– Will probably move to IPv6 “from the edges in”

• IPv6 will be adopted– First by smaller organizations with greater flexibility

and higher tolerance for difficulties of pioneering

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IPv6 Rate of Adoption

• Biggest push for the adoption of IPv6 I– Coming from those who were not a part of the initial

Internet “land rush” of the 1990s

• New technologies (cellular phones) have two reasons to embrace IPv6– They want the address space– Communications technologies need the improved

functionality of the IPv6 protocol suite

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Transitioning to IPv6: The Reality

• Reaction of industry participants to potential of IPv6– Initially, service provider segment of the market

pushed for the protocol– Router and switch vendors saw the protocol as a

marketing opportunity– Engineers in the service provider space saw IPv6 as

a solution to solve a specific problem

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Interoperability

• One technology can work together with another technology

• Network address translation (NAT) – Used to provide translation between private IP

addresses and public IP addresses

• Transitioning to IPv6 – The movement of deploying IPv6 throughout a

production environment

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Network Elements

• Clients

• Servers

• Routers

• Gateways

• VoIP networks

• Network management nodes

• Transition nodes

• Firewalls

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Software

• Tools and utilities designed to monitor, report on, and manage network infrastructure elements – Network management and utilities– Network Internet infrastructure applications– Network systems applications– Network end-user applications– Network high-availability software– Network security software

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Transitioning to IPv6 from the Windows Perspective

• Microsoft provides support for IPv6 implementations for – Windows Server 2003– Windows XP with Service Pack 1 (or higher)– Windows CE.NET 4.1

• Microsoft – Supports the Intra-Site Automatic Tunnel Addressing

Protocol (ISATAP)

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Availability

• Most of the IPv6 deployments are– In Asia and Europe– In areas that were behind the deployment of IPv4

infrastructures

• These environments are ahead of the curve for two reasons– Market is forcing IPv6 onto the consumers, which

creates demand for provider support– A lot of the solutions are deployed initially with IPv6

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Summary

• Adopting the new version of the Internet Protocol– Would solve the IP address shortage

• For backward compatibility– IPv6 defines two mechanisms (IPv4-compatible and

IPv4-mapped addresses)

• IPv6 supports great improvements to – Communications security, auto-configuration– Quality of Service handling– Routing efficiency and mobile use

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Summary (continued)

• IPv6 builds on lessons learned in IPv4 to – Streamline headers, allocate and aggregate

addresses, and generally improve routing behavior

• IPv6 introduces a Neighbor Discovery protocol

• Basic IPv6 packet format – Redesigned to streamline processing time en route

to and at its intended destination(s)

• IPv6 makes it easier to renumber networks than with IPv4

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Summary (continued)

• IPv6 – Embeds robust, built-in security in its required core

implementation– Incorporates incremental updates to most core IP

protocols

• Mobile IPv6 – Enables mobile users to operate even though they

may move from one location to another

• Obstacles to widespread deployment of IPv6 – IPv4/IPv6 interoperability– Availability of IPv6 addresses