Module 18 IP Version 6

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Module 18IP Version 6
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• Textbook sections
• BF Section 25.1 IPv6
• BF Section 25.2 IPv6 Addresses
• BF Section 25.3 IPv6 Packet Format
• Topics
• Overview
• Addresses
• Terminology
• Text Representation
• Address Space Assignment
• Transition from IPv4 to IPv6
• Packet Format
• Base Header
• Extension Header
• Comparison between IPv4 and IPv6 packet

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1. Overview

• Major changes
• Extended address space
• IPv6 has 128-bit source and destination addresses
  (4 times larger than IPv4)
• Simplified and extensible header format
• IPv6 header are designed to keep the IP header to
  a minimum by moving nonessential fields and
  option fields to extension headers that are
  placed after the IP header.
• IPv6 can easily be extended for unforeseen
  feature through the adding of extension headers
  after the IPv6 base header. Support for new
  hardware or application technologies is built in.
• Support for time-dependent traffic
• A new field in the IPv6 header allows the
  pre-allocation of network resources along a path
  so that time-dependent services such as voice and
  video are guaranteed a requested bandwidth with a
  fixed delay.
• Security features
• Extensions to support authentication, data
  integrity, and (optional) data confidentiality
  are specified for IPv6

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1. Overview

• Douglas E. Comer
• It took many years for the IETF to formulate a
  new version of IP. Because the IETF produces
  open standards, it invited the entire community
  to participate in the process. Computer
  manufacturers, hardware and software vendors,
  users, managers, programmers, telephone
  companies, and the cable television industry all
  specified their requirements for the next version
  IP, and all commented on specific proposals.
• choosing a new version of IP was not easy. The
  popularity of the Internet means that the market
  for IP products around the world is staggering.
  Many groups see the economic opportunity, and
  hope that the new version of IP will help them
  gain an edge over the competition. In addition,
  personalities have been involved _ some
  individuals hold strong technical opinions
  others see active participation as a path to a
  promotion. Consequently, the discussions
  generated heated arguments.

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2. Addresses - Terminology

• Terminology
• Node A device that implements IPv6
• Host any node that is not a router
• Link a communication facility or medium over
  which nodes can communicate at the data link
  layer, i.e., the layer immediately below IPV6.
  Examples are Ethernet PPP links.
• Interface a nodes attachment to a link
• Neighbors nodes attached to the same link
• Address an IPv6-layer identifier for an
  interface or a set of interfaces

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2. Addresses - Terminology

• IPv6 addresses are 128 bit identifies for
  interfaces and sets of interfaces
• Three types of addresses
• Unicast address
• An identifier for a single interface. A packet
  sent to an unicast address is delivered to the
  interface identified by that address.
• Anycast address
• An identifier for a set of interfaces (typically
  belonging to different nodes). A packet sent to
  an anycast address is delivered to one of the
  interfaces identified by that address (the
  nearest one, according to the routing
  protocols measure of distance).
• Multicast address
• An identifier for a set of interfaces (typically
  belonging to different nodes). A packet sent to
  a multicast address is delivered to all
  interfaces identified by that address.
• There are no broadcast addresses in IPv6, their
  function being superseded by multicast addresses

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2. Addresses Text Representation

• An IPv6 address consists of 16 bytes it is 128
  bits long
• Colon hexadecimal notation (abbreviated colon
  hex)
• In this notation, 128 bits are divided into eight
  sections
• Each section is two bytes in length.
• Two bytes in hexadecimal notation requires four
  hexadecimal digits
• Abbreviation
• Within a section, the leading zeros of a section
  can be omitted. However, trailing zeros can not
  be omitted
• Between sections, consecutive sections consisting
  of zeros only can be replaced by a double colon.
  (Note that this type of abbreviation is allowed
  only one per address.)

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BF Figure 25-1 IPv6 address
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BF Figure 25-2 Abbreviated address
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BF Figure 25-3 Abbreviated address with
consecutive zeros
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2. Addresses Address Space Assignment

• Address structure
• The address is divided into two parts. The first
  par is called the type prefix.
• Type prefix
• Variable length
• Defines the purpose of the address
• The codes are designed such that no code is
  identical to the first part of any other code
• When an address is given, the type prefix can
  easily be determined

BF Figure 25-5 Address structure
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Table 25.1 Type prefixes for IPv6 addresses
(partial list)
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2. Addresses Address Space Assignment

• Provider-Based unicast addresses
• Fields

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BF Figure 25-6 Provider-based address
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2. Addresses Address Space Assignment

• Provide-Based unicast addresses
• Address hierarchy IPv6 nodes may have
  considerable or little knowledge of the internal
  structure of the IPv6, depending on the role the
  node plays (for instance, host versus router)
• At a minimum, a node may consider that unicast
  addresses (including its own) have no internal
  structure
• A slightly sophisticated host (but still rather
  simple) may additionally be aware of subnet
  prefix(es) for th link(s) it is attached to,
  where different addresses may have different
  values for the number of bits of subnet prefix
• Routers will more generally have knowledge of one
  or more of the hierarchical boundaries for the
  operation of routing protocols.

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BF Figure 25-7 Address hierarchy
Note The difference between a field and a
prefix. For example, the difference between
subnet identifier and Subnet prefix.
Example a host has the address
581E14562324ABCD0000000000001211 Assume
that the node identifier is 48 bits (6 bytes),
the subnet identifier is 32 bits (4 bytes), and
subscriber identifier is 24 bits (3 bytes). Then
the provider prefix is 581E14 (binary
representation 0101 1000 0001 1110 0001 0100
Defines the address as a provider-based address
Registry identifier INTERNIC
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2. Addresses Address Space Assignment

• Anycast address
• Anycast addresses are syntactically
  indistinguishable from unicast addresses.
• Anycast addresses are allocated from the unicast
  address space, using any of the defined unicast
  address formats.
• When a unicast address is assigned to more than
  one interface, thus turning it into an anycast
  address, the nodes to which the address is
  assigned must be explicitly configured to know
  that it is an anycast address.
• Expected use of anycast addresses
• To identify the set of routers belonging to an
  organization providing internet service
• To identify the set of routers attached to a
  particular subnet, or the set of routers
  providing entry into a particular routing domain
• Restrictions imposed on IPv6 anycast addresses
• An anycast address must not be used as the source
  address of an IPv6 packet
• An anycast address must not be assigned to an
  IPv6 host, that is, it may be assigned to an IPv6
  router only.

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2. Addresses Address Space Assignment

• Reserved addresses
• The unspecified address
• The address 00000000 is called the
  unspecified address
• It must never be assigned to any node. It
  indicates the absence of an address
• One example of its use is in the Source Address
  field in the IPv6 header of any IPv6 packets sent
  by an initializing host before it has learned its
  own address.
• Loopback address
• The unicast address 00000001 is called the
  loopback address
• It may be used by a node to send an IPv6 packet
  to itself
• It may never be assigned to any physical
  interface
• An IPv6 packet with a destination address of
  loopback must never be sent outside a single node
  and must never be forward by an IPv6 router.

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2. Addresses Address Space Assignment

• Link local addresses
• Link local addresses may be used if a site or
  organization having a LAN uses the Internet
  protocols but is not connected to the Internet.
• When the site or organization connects to the
  global Internet, it can then form global
  addresses by replacing the link local prefix with
  a subnet prefix.
• Routers must not forward any packets with link
  local source addresses outside of the site.

BF Figure 25-12 Link local address
Link local prefix
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2. Addresses Address Space Assignment

• Site local addresses
• Site local addresses may be used if a site
  having several networks uses the Internet
  protocols but is not connected to the Internet.
• When the site connects to the global Internet,
  it can then form global addresses by replacing
  the site-local prefix with a subscriber prefix.
• Routers must not forward any packets with site
  local source addresses outside of the site.

BF Figure 25-13 Site local address
Site local prefix
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2. Addresses Address Space Assignment

• Multicast addresses
• An IPv6 multicast address is an identifier for
  a group of nodes.
• A node may belong to any number of multicast
  groups.
• Multicast address must not be used as source
  addresses in IPv6 datagrams or appear in any
  routing header.

BF Figure 25-14 Multicast address
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2. Addresses Transition from IPv4 to IPv6

• The IPv6 transition mechanisms include a
  technique for hosts and routers to dynamically
  tunnel IPv6 packets over IPv4 routing
  infrastructure.
• Special IPv6 unicast addresses are provide by
  IPv6 that carry an IPv4 address in the low-order
  32-bits.
• Compatible address
• an address of 96 bits of zero followed by 32 bits
  of IPv4 address
• Used when a computer using IPv6 wants to send a
  message to another computer using IPv6. However,
  the packet should pass through a region where the
  networks are still using IPv4
• Mapped address
• An address of 80 bits of zero, followed by 16
  bits of one, followed by the 32-bit IPv4 address.
• Used when a computer using IPv6 wants to send a
  message to another computer still using IPv4.
  The packet travels mostly through IPv6 network.

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BF Figure 25-10 Compatible address
Corresponding to
BF Figure 25-11 Mapped address
Corresponding to
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2. Addresses Transition from IPv4 to IPv6
BF Figure 25-48 Three transition strategies

• Dual stack a host supports both IPv4 and IPv6
  simultaneously.
• Tunneling is used when two IPv6 hosts need to
  communicate with each other through an IPv4
  region.
• Header translation An IPv6 sending host needs
  to communicate with an IPv4 receiving host
  through an IPv6 region.

• Definitions
• Tunneling
• - The practice of encapsulating a datagram from
  one protocol into a second protocol and using
  the second protocol to transverse a network.
• - At the destination, the encapsulation is
  stripped off and the original message is
  reintroduced to the network. Tunneling is also
  referred to as encapsulation.
• Encapsulation
• - In the internetworking community, to surround
  one protocol with another protocol for the
  purpose of passing the foreign protocol through
  the native environment.

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BF Figure 25-49 Dual stack
To determine which version to use when sending a
packet to a destination, the source host queries
the DNS If the DNS returns an IPv4 address, the
source host sends an IPv4 packet. If the DNS
returns an IPv6 address, the source host sends an
IPv6 packet.
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BF Figure 25-50 Automatic tunneling
Automatic tunneling is applicable if the
receiving host uses a IPv6 compatible address.
The destination host, which is using a dual
stack, passes the packet to the IPv6 software for
processing
This router encapsulates an IPv6 packet in an
IPv4 packet.
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BF Figure 25-51 Configured tunneling
Configured tunneling is used when the receiving
host does not support an IPv6 compatible address.
This router encapsulates the IPv6 packet in an
IPv4 packet using its own IPv4 address as the
source and the other routers IPv4 address as the
destination
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BF Figure 25-52 Header translation
Header translation is used when the majority of
the Internet has moved to IPv6 but some system
still use IPv4. The sender wants to use IPv6, but
the receiver does not understand IPv6. Tunneling
does not work in this situation because the
packet must be in the IPv4 format to be
understood by the receiver.
This router converts the header of the IPv6
packet to an IPv4 header
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3. Packet Format Base Header
BF Figure 25-15 IPv6 datagram
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Figure 25-16 IPv6 datagram format
4 bytes
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3. Packet Format Base Header

• VER
• Four-bit field defines the version of the IP. For
  IPv6, the value is 6
• PRI
• The four-bit field defines the priority of the
  packet with respect to traffic congestion.
• Two categories
• Congestion-controlled Packets may arrive delayed
  or even lost or received out of order

Table 25.3 Priorities for congestion-controlled
traffic
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3. Packet Format Base Header

• No congestion-controlled
• This refers to a type of traffic that expects
  minimum delay. Discarding of packets is not
  desirable. Retransmission in most cases is
  impossible. Real-time audio and video are good
  examples of this type of traffic
• The priorities are usually assigned based on how
  much the quality of received data can be affected
  by discarding some packets. Data containing less
  redundancy (such as low-fidelity audio or video)
  can be given a higher priority.

Table 25.4 Priorities for noncongestion-controlled
traffic
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3. Packet Format Base Header

• Flow label
• Payload length
• This two-byte payload field defines the total
  length of the IP datagram excluding the base
  header

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3. Packet Format Base Header

• Next header
• An eight-bit field defining the header that
  follows the base header in the datagram. The
  next header is either one of the optional
  extension headers used by IP or the header for an
  upper layer protocol such as UDP or TCP

Table 25.2 Next header codes
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3. Packet Format Base Header

• Hop limit
• This eight-bit hop limit field serves the same
  purpose as the TTL field in IPv4.
• Decremented by 1 by each node that forwards the
  packet. The packet is discarded if Hop limit is
  decremented to zero.
• Source address
• Destination address
• Usually identifies the final destination of the
  datagram. However, if source routing is used,
  this field contains the address of the next
  router.

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3. Packet Format Extension Header
BF Figure 25-17 Extension header format
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3. Packet Format Extension Header

• Extension Headers
• Hop-by-hop option
• Source routing
• Fragmentation
• Authentication
• Encrypted security payload
• Destination option

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BF Figure 25-19 Hop-by-hop option header format
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BF Figure 25-20 The format of options in a
hop-by-hop option header
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BF Figure 25-21 Pad1
BF Figure 25-22 PadN
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BF Figure 25-23 Jumbo payload
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3. Packet Format Extension Header

• Source routing option
• Header length
• The header length specifies the length of the
  routing extension header in units of 64 bits, not
  including the first 64 bits
• Type
• The type field defines loose or strict routing
• Currently, only type 0 is specified
• Strict/loose Mask (RFC 1752)
• Determines the rigidity of routing
• The mask is used when making a forwarding
  decision.
• If the value of the Next Hop pointer field is N,
  and the Nth bit in the strict/loose bit mask
  field is set to 1, it indicates that the next hop
  is a strict source route hop
• If this bit is set to 0, it indicates that the
  next hop is a lose source route hop (24 bit bit
  pattern)

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3. Packet Format Extension Header

• Address/segment left
• Identifies the number of route segments remaining
  before the destination is reached.
• Initially, this value will be set to the total
  number of route segments from the source to the
  destination
• Each route decrements this value by 1 until the
  packet reaches the destination
• Changing addresses
• The destination address does not conform to
  previous definition (the final destination of the
  datagram). Instead, it changes from router to
  router
• The addresses in the extension header also change
  from router to router

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BF Figure 25-24 Source routing
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BF Figure 25-25 Source routing example
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3. Packet Format Extension Header

• Fragmentation
• Only the original source can fragment
• Fragmentation offset field
• Measured in units of eight bytes
• M flag
• 1 more fragments
• 0 last fragment
• Fragment identification
• For every packet that is to be fragmented, the
  source node generates an identification value.

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BF Figure 25-26 Fragmentation
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3. Packet Format Extension Header

• Authentication

BF Figure 25-27 Authentication
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BF Figure 25-28 Calculation of authentication
data
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3. Packet Format Extension Header

• Encrypted security payload

BF Figure 25-29 Encrypted security payload
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BF Figure 25-30 Transport mode encryption
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BF Figure 25-31 Tunnel-mode encryption
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3. Packet Format Comparison between IPv4 and
IPv6 packet

• Table 25.5 Comparison between IPv4 and IPv6
  packet header
• The header length field is eliminated in IPv6
  because the length of the header is fixed in this
  version
• The service type field is eliminated in IPv6.
  The priority and flow label fields together take
  over the function of the service type field.
• The total length field is eliminated in IPv6 and
  replaced by the payload length field
• The identification , flag, and offset fields are
  eliminated from the base header in IPv6. They
  are included in the fragmentation extension
  header.
• The TTL field is called hop limits in IPv6.
• The protocol field is replaced by the next header
  field.
• The header checksum is eliminated because the
  checksum is provided by upper layer protocol it
  is thereby not needed at this level.
• The option fields in IPv4 are implemented as
  extension header in IPv6

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3. Packet Format Comparison between IPv4 and
IPv6 packet

• Table 25.6 Comparison between the options in IPv4
  with the extension headers in IPv6
• The no-operation and end-of-option in IPv4 are
  replaced by Pad1 and PadN options in IPv6
• The record route option is not implemented in
  IPv6 because it was not used.
• The timestamp option is not implemented because
  it was not used
• The source route option is called the source
  route extension header in IPv6.
• The fragmentation fields in the base header
  section of IPv4 have moved to the fragmentation
  extension header in IPv6.
• The authentication extension header is new in
  IPv6.
• The encrypted security payload extension header
  is new in IPv6.