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The Future of TCP/IP (IPv6)
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Chapter 33
Evolution of TCP/IP intertwined with
evolution of the global Internet
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Internet is largest installed internet
Funding comes from organizations that are
Internet users
Most researchers use Internet daily
Chapter purpose is to consider ongoing
evolution of TCP/IP
© MMII JW Ryder
CS 428 Computer Networking
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Why Change?
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New computer and communication
technologies
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New applications
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New technologies = new possibilities and needs
New ways to use Internet means new protocols
needed
Increases in size and load
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Massive growth means old ways strained
© MMII JW Ryder
CS 428 Computer Networking
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Motivation for Changing IPv4
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New countries with differing administrative policies
IPv4 same for about 20 years
Since IPv4 designed
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Enhanced processor performance
Memory size increased
Network bandwidth for Internet backbone increased
New LAN technologies
Number of hosts on Internet risen to over 56 million
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CS 428 Computer Networking
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Road to New Version of IP
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Several suggested designs
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Make IP more sophisticated at expense of
increased complexity and processing overhead
Use a modification of OSI CLNS protocol
Retain most of ideas in IP but make simple
extensions to accommodate larger addresses
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Simple IP – (SIP)
Still include new ideas from other suggested protocols
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Features of IPv6
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Despite many conceptual similarities IPv6
changes most protocol details
Completely revises datagram format
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Replace IPv4 variable length fields with a series
of fixed format headers
Still supports connectionless delivery
Allows sender to choose datagram size but
requires sender to specify maximum hops
© MMII JW Ryder
CS 428 Computer Networking
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Features of IPv6
Includes facilities for fragmentation and source
routing
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Main changes introduced are
1. Larger Addresses: IPv6 quadruples the size from 32
bits to 128 bits
2. Extended Address Hierarchy: Creates ability to have
additional address levels on an internet
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IPv4 Addresses – 2 levels, Network and Host
IPv6 Addresses – Can define a hierarchy of ISPs as well
as hierarchy within a site
© MMII JW Ryder
CS 428 Computer Networking
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Features of IPv6
3. Flexible Header Format: Datagram format
entirely different
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Defines a fixed size (40 octets) header with
optional extended headers
4. Improved Options:
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Has same options as IPv4 plus some new ones
5. Provision for Protocol Extension:
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Move away from protocol that fully specifies all
details to one that permits additional features
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CS 428 Computer Networking
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Features of IPv6
6. Support for Autoconfiguration and
Renumbering:
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Allows computers on an isolated network to
assign themselves addresses and begin
communicating without depending on a router or
manual configuration
Facility to permit a manager to renumber
networks dynamically
© MMII JW Ryder
CS 428 Computer Networking
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Features of IPv6
7. Support for Resource Allocation:
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Two facilities for pre-allocation of network
resources
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a Flow abstraction
a Differentiated Services specification
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IPv6 Address Space
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How big is 2128 ?
So large that everyone on earth will have enough
addresses to have their own internets with as many
addresses as the current Internet has
So large that there would be 1024 internet addresses
per each square meter on earth
So large that the address space is greater than 3.4 *
1038
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If addresses are assigned at the rate of 1,000,000 every
microsecond (1/1,000,000th of a second), it would take
more than 1020 years to assign all possible addresses
© MMII JW Ryder
CS 428 Computer Networking
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IPv6 Colon Hexadecimal Notation
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128 bit number expressed as dotted decimal
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104.230.140.100.255.255.255.255.0.0.17.128.150.10.255.255 becomes
68E6:8C64:FFFF:FFFF:0:1180:96A:FFFF
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Hex notation allows zero compression
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A string of repeated zeros is replaced with a pair
of colons
FF05:0:0:0:0:0:0:B3 becomes FF05::B3
Can be applied only once in any address
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CS 428 Computer Networking
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Zero Suppression
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0:0:0:0:0:0:128.10.2.1 becomes ::128.10.2.1
Looks quite similar to IPv4
12AB::CD30:0:0:0:0/60 says use first 60 bits
and becomes
12AB00000000CD3
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CS 428 Computer Networking
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Basic IPv6 Address Types
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Unicast – Destination address specifies a
single computer. Route datagram along
shortest path.
Anycast – Destination is a set of computers,
possibly at different locations, that all share a
single address. Route datagram along shortest
path and deliver to exactly one member of the
group (i.e. closest member)
© MMII JW Ryder
CS 428 Computer Networking
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Basic IPv6 Address Types
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Multicast - Destination is a set of computers,
possibly at different locations. One copy of
the datagram will be delivered to each
member of the group using hardware
multicast or broadcast if viable.
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CS 428 Computer Networking
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Encoding IPv4 Addresses in IPv6
80 zero bits
16 bits
32 bits
0000 . . . . . . . . . . . . . . . . . . . . . . . . 0000
0000
IPv4 Address
0000 . . . . . . . . . . .. . . . . . . . . . . . . . 0000
FFFF
IPv4 Address
• 16-bit field contains 0000 if node also has a conventional IPv6 address
and FFFF if it does not.
RESERVED
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DATAGRAM IDENTIFICATION
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General Form of IPv6 Datagram
Optional
Base
Extension
Header
Header 1

Extension
Header N
Data
40 octets
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CS 428 Computer Networking
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IPv6 Base Header Format
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See Base Header figure
Alignment changed from 32 bit to 64 bit multiples
Header length eliminated – Replaced with
PAYLOAD LENGTH field
Size of source and destination addresses changed to
16 octets
Fragmentation information moved out of fixed fields
in base header to extension header
© MMII JW Ryder
CS 428 Computer Networking
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IPv6 Base Header Format
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TIME-TO-LIVE field changed to HOP LIMIT
SERVICE-TYPE field renamed to TRAFFIC
CLASS and extended with FLOW LABEL
field
PROTOCOL field replaced with a field that
specifies type of next header
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CS 428 Computer Networking
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Base Header Format
0
4
VERS
12
16
TRAFFIC CLASS
PAYLOAD LENGTH
24
31
FLOW LABEL
NEXT HEADER
HOP LIMIT
SOURCE ADDRESS
DESTINATION ADDRESS
Base Header Size: 4 + 4 + 16 + 16 = 40 Octets
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CS 428 Computer Networking
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Base Header Format
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PAYLOAD LENGTH is length of all
extension headers plus data
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i.e. Total length – 40 octets (Base Header)
IPv6 datagram can contain up to 64K octets of
data
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CS 428 Computer Networking
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Traffic Class
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IPv4 SERVICE CLASS renamed to TRAFFIC
CLASS
New IPv6 mechanism allows for resource
reservation!
A router can associate with each datagram a given
resource allocation
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Abstraction called a FLOW
A FLOW is a path through an internet along which
intermediate routers guarantee a certain level of
quality of service
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CS 428 Computer Networking
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Traffic Class
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FLOW LABEL in the base header contains a
label that routers use to map a datagram to a
certain specific flow and priority
Flows can also be used within an organization
to manage network resources
Example
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Two applications that need to send and receive
video can establish a flow over which the
bandwidth and delay are guaranteed
© MMII JW Ryder
CS 428 Computer Networking
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IPv6 Extension Headers
Base Header
NEXT=TCP
TCP Segment
One Base Header
Base Header
NEXT=ROUTE
Route Header
NEXT=TCP
TCP Segment
Route Header
NEXT=AUTH
Auth Header
NEXT=TCP
Two Base Headers
Base Header
NEXT=ROUTE
TCP Segment
Three Base Headers
© MMII JW Ryder
CS 428 Computer Networking
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IPv6 Fragmentation
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As with IPv4, IPv6 arranges for destination to
perform re-assembly
In IPv6 however, changes were made that avoid
fragmentation by routers
IPv4 requires intermediate routers to fragment any
datagram that is too large for the maximum
transfer/transmission unit (MTU) of network over
which it must travel
IPv6 fragmentation is end-to-end
© MMII JW Ryder
CS 428 Computer Networking
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IPv6 Fragmentation
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No fragmentation done on intermediate
routers
Source which is responsible for fragmentation
has two choices
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Use guaranteed minimum MTU (1280 octets)
Perform Path MTU Discovery
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Identifies minimum MTU along path to the
destination
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IPv6 Fragmentation
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Either case, the source fragments data
IPv6 fragmentation inserts a small extension
header after the base header in each fragment
0
8
NEXT HEADER
16
RESERVED
24
FRAG. OFFSET
29 31
RS M
DATAGRAM IDENTIFICATION
RS is set t 0 and reserved. M marks last fragment. ID unique for re-assembly.
Fragments must be a multiple of 8 octets.
© MMII JW Ryder
CS 428 Computer Networking
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