The Future of TCP/IPand IPv6

Chapter 33

Introduction

• Why is TCP/IP technology important to the evolution of the Internet?– The Internet is the largest TCP/IP internet

– Funding for research and engineering comes from companies that use the Internet

– Most researchers use the Internet daily and are motivated to solve problems and extend capabilities

Why Change?

• New technology• New applications• Increase in size and load

– Doubling every 9 months

New Policies

• More national backbones attach• Policies for interaction must be determined and

enforced

Motivation for Changing IPv4

• IP version 4 has remained almost unchanged since the late 1970’s– It has worked well

• What has changed since its inception?– Processor Performance - increased by 2 orders of magnitude

– Memory Size - increased by over 100 times

– Network Bandwidth - increase by 7000 times

– LAN Technologies - emerged

– Number of Hosts - > 56 million

• Most obvious need: more address space

The Name of the Next IP

• IP version 6• Previous IP versions

– Versions 1 and 3 were never formally assigned

– Version 5 was an experimental Stream Protocol that was probably misnamed

Features of IPv6

• IPv6 retains much of IPv6• Categories of Changes

– Larger Addresses - 128 bits

– Extended Address Hierarchy

– Flexible Header Format

– New Options

– Protocol Extensibility

– Autoconfiguration and Network Renumbering

– Preallocation of Network Resources

General Form of IPv6 Datagram

• Contains a fixed-size base header, zero or more extension headers and data

Data...ExtensionHeader 1

ExtensionHeader N

... BaseHeader

optional

IPv6 Base Header Format

• The base header contains less than the IP header– Several things have been moved to extension headers

Destination Address (128 bits)

Source Address (128 bits)

Payload Length Next hdr Hop Limitvers Class Flow Label

IPv6 Base Header Format

• The base header is fixed at 40 octets• Payload Length is the size of the datagram only

– Thus, a datagram could be 64K octets

• Traffic Class is the same as the Type of Service• Flow Label contains information that routers use

to associate a datagram with a flow and priority– A flow consists of a path through an internet which

guarantees a quality of service• Used to guarantee or restrict quality of service

IPv6 Extension Headers

• Compromise of generality and efficiency– Includes mechanisms to support fragmentation, source

routing, authentication, etc.

– Putting all possible mechanisms in the datagram header may be wasteful if not used

• Similar to options in IPv4• Each datagram includes extension headers for only

those facilities used by the datagram

Parsing an IPv6 Datagram

• The base header and extension headers have a Next Header field which indicates the type of header that follows– At intermediate routers, the base headers and the hop-

by-hop extension headers are examined

Fragmentation and Reassembly

• The designers of IPv6 tried to avoid fragmentation by routers– The source fragments the data according to one of the

following:• It can use the guaranteed minimum MTU of 1280 octets

• It can perform Path MTU Discovery to find the minimum MTU along the path

– When fragmentation is needed, the source inserts an extension header after the base header in each fragment

Datagram Identification

Next Header Reserved Fragment Offset RS M

Consequence of End-to-End Fragmentation• In IPv4, we assumed that routes can change

dynamically• In IPv6, route changes mean that the path MTU

may be different– If the path MTU along a new route is less than the path

MTU along the original route, either• the intermediate router fragments the datagram

• or the original source must be notified

– A new ICMP message informs the source which can do another path MTU discovery to refragment

IPv6 Source Routing

• An extension header is used to specify routing options– The first four fields are fixed:

• next header

• header extension length

• routing type - only type available is 0, loose source routing

• segments left - number of addresses remaining in the list

– Type-specific data - list of addresses of routers through which the datagram must pass

Type-specific data ...

Next header Hdr Ext Len Route Type Seg Left

IPv6 Options

• The next header field of the previous header distinguishes between two types of extension headers

– Hop By Hop Extension Header• Examined at each hop

– End To End Extension Header• Interpreted only at the destination

• The format of an IPv6 option extension header

Next header Header Len

One or more Options

IPv6 Options

• Within the options portion of the header the options are coded as

• Where the first two bits in Type indicate– 00 skip this option– 01 discard datagram; do not send ICMP message– 10 discard datagram; send ICMP message to source– 11 discard datagram; send ICMP for non-multicast

• The third bit in Type indicates whether the option can change in transit

Type (8 bits) Length (8 bits) Data for this option

IPv6 Colon Hexadecimal Notation• Binary and decimal notations are too cumbersome,

so addresses are represented in colon hex notation– Zero compression replaces a string of repeated zeroes

with a pair of colons (only once in the notation)

– CIDR-like notation is used when an address is followed by a slash and a number of bits

Three Basic IPv6 Address Types

• Destination addresses on a datagram fall into 3 categories– Unicast - the destination is a single computer

– Anycast - the destination is a set of computers that all share the same address, and the datagram should be delivered to the closest one (along the shortest path)

– Multicast - the destination is a set of computers that all share the same address, and the datagram should be delivered to each one

Broadcast and Multicast

• Broadcasting is treated as a special form of multicasting

• Direct communication is handled best by unicast and group communication is handled best by multicast and broadcast

Proposed IPv6 Address Assignment• How to manage address assignment?

– The large address space permits a multi-level hierarchy as opposed to the current two-level hierarchy of (network, host)

• How to map an address to a route (examine a datagram and choose a path to the destination)?

• See the proposed division in Figure 33.8

Transition from IPv4

• Some of the addresses with a prefix of 0000 0000 will be used for embedded IPv4 addresses

• Why is encoding necessary?– A computer may be upgraded before it gets an IPv6 @

– A computer running IPv6 may need to communicate with an computer running IPv4

IPv4 address0000 . . . . . . . . . . . . . . . . . . 0000 FFFF

0000 . . . . . . . . . . . . . . . . . . 00000000 . . . . . . . . . . . . . . . . . . 0000 0000 IPv4 address

80 zero bits 16 bits 32 bits

Unicast Address Hierarchy

• Three conceptual levels– Level 1 - Globally known public topology

• Major ISPs that provide long-haul service to subscribers

• Exchanges which interconnect ISPs and individual subscribers not specifying an ISP (allows freedom to move between ISPs)

– Level 2 - Individual site• A set of computers and networks located at a site (implies

physically contiguous and within an organization)

– Level 3 - Individual network interface• A single attachment between a computer and a network

Aggregatable Global Unicast Address Structure• Authority for assigning IPv6 addresses flows

down a hierarchy– Each top-level organization (ISP or exchange) is

assigned a unique prefix• Organizations which subscribe to that top-level ISP are

assigned a unique number for their site– Managers assign numbers to each network connection

Interface IDSLAIDP TLA ID R NLA ID

64 bits16248133

third levelsiteleveltop level

Aggregatable Global Unicast Address Structure• TLA ID - top level ID assigned to the ISP or

exchange that owns the address• NLA ID - next level ID • SLA ID - specific site ID• Each may be further divided as needed

Interface Identifiers

• The low-order 64 bits are large enough to accommodate te interface hardware address– ARP is not needed to resolve to a hardware address

– IPv6 standards specify how to encode various forms of hardware address

• IEEE has a 64-bit address format called EUI-64

• Figure 33.12 shows how an IEEE 802 address can be encoded

in the low order 64 bits of an IPv6 address

Local Addresses

• Link-local addresses are restricted to a single network

• Site-local addresses are restricted to a single site• Routers do not forward datagrams with locally-

scoped addresses outside the specified scope • This gives us the concept of private addresses or

nonroutable addresses

Autoconfiguration and Renumbering• A host on an isolated network generates a unique

link-local address– That address is used to discover routers and obtain site-

local and global prefix information

• To facilitate network renumbering, routers limit the time that a computer retains a prefix

Summary

• IPv6 retains many features of IPv4• Some differences:

– Format

– Authentication is provided

– Flow labeling

– Datagrams are organized as a series of headers (base and one or more extensions) followed by data

– Addresses are 128 bits long

For Next Time

• Final Exam