Next Generation IP Protocol: IPv6

1
Next Generation IP ProtocolIPv6

• NETE0514
• Presented by
• Dr.Apichan Kanjanavapastit

2
Why IPv6?

• IPv4 has some deficiencies that make it
  unsuitable for the fast-growing Internet,
  including the following
• Fast-spreading use of the Internet, and new
  services, such as Mobile IP and IP telephony lead
  to the depletion of the IP addresses
• The Internet must accommodate real-time audio and
  video transmission
• The Internet must accommodate encryption and
  authentication of data for some applications

3
What IPv6?

• To overcome the deficiencies of IPv4, IPv6
  (Internetworking Protocol, version 6), also known
  as IPng (Internetworking Protocol, next
  generation) was proposed
• In IPv6, the Internet protocol was extensively
  modified to accommodate the unforeseen growth of
  the Internet
• The format and the length of the IP addresses
  were changed along with the packet format
• Related protocols, such as ICMP, were also
  modified

4
What IPv6? (cont.)

• Other protocols in the network layer, such as
  ARP, RARP and IGMP, were either deleted or
  included in the ICMPv6 protocol
• Routing protocols, such as RIP and OSPF, were
  also slightly modified to accommodate these
  changes

5
Reason for Delay in Adoption of IPv6

• The adoption of IPv6 has been slow
• The reason is that the depletion of IPv4
  addresses has been slowed down because of 3
  short-term remedies
• Classless addressing
• Use of DHCP for dynamic address allocation
• NAT
• However, the fast-spreading use of the Internet,
  and new services, may require the total
  replacement of IPv4 with IPv6 in the future

6
Advantages of IPv6 over IPv4

• Larger address space. An IPv6 address is 128 bits
  long. Compared with the 32-bit address of IPv4
• Better header format. Options of IPv6 are
  separated from the base header and inserted, when
  needed, between the base header and the
  upper-layer data. This simplifies and speeds up
  the routing process
• New options. IPv6 has new options to allow for
  additional functionalities
• Allowance for extension. IPv6 is designed to
  allow the extension of the protocol if required
  by new technologies or applications
• Support for resource allocation. There are 2 new
  fields, traffic class and flow label have been
  added to enable the source to request special
  handling of the packet
• Support for more security. The encryption and
  authentication options provide confidentiality
  and integrity of the packet

7
IPv6 Addresses

• An IPv6 address consists of 16 bytes (octets) it
  is 128 bits long
• A computer normally stores the address in binary,
  but it is clear that 128 bits cannot easily be
  handled by humans
• Several notations have been proposed to represent
  IPv6 addresses when they are handled by humans

8
Dotted-Decimal Notation

• To be compatible with IPv4 addresses, one can use
  dotted-decimal notation as used in IPv4 addresses
• However, this notation is inconvenient for
  16-byte IPv6 addresses since it is too long
• This notation is therefore rarely used except
  partially

221.14.65.11.105.45.170.34.12.234.18.0.14.0.115.22
5
9
Colon Hexadecimal Notation

• In this notation, 128 bits are divided into 8
  sections, each 2 bytes in length
• Two bytes in hexadecimal notation require 4
  hexadecimal digits. Therefore, the address
  consists of 32 hexadecimal digits, with every 4
  digits separated by a colon

10
Abbreviation of IPv6 addresses

• If many of the digits are zeros, we can
  abbreviate the address
• The leading zeros of a section (4 digits between
  2 colons) can be omitted
• Only the leading zeros can be dropped, not the
  trailing zeros

11
Zero Compression

• Further abbreviations, often called zero
  compression, are possible if there are
  consecutive sections consisting of zeros only
• We can remove the zeros altogether and replace
  them with a double semicolon
• This type of abbreviation is allowed only once
  per address. If there are two runs of zero
  sections, only one of them can be abbreviated

12
Mixed Representation

• Sometimes we see a mixed representation of an
  IPv6 address colon hex and dotted-decimal
  notation
• This is appropriate during the transition period
  in which an IPv4 address is embedded in an IPv6
  address (as the rightmost 32 bits)

FDEC14AB2311BBFEAAAABBBB130.24.24.18
13
CIDR Notation

• Since IPv6 uses hierarchical addressing, IPv6
  then allows classless addressing and CIDR notation

14
Show the unabbreviated colon hex notation for the
following IPv6 addresses a. An address with 64
0s followed by 64 1s. b. An address with 128
0s. c. An address with 128 1s. d. An address with
128 alternative 1s and 0s. Solution a.
0000000000000000FFFFFFFFFFFFFFFF b.
00000000000000000000000000000000 c.
FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF d.
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
15
The following shows the zero contraction version
of addresses in Example 26.1 (part c and d cannot
be abbreviated) a. FFFFFFFFFFFFFFFF b.
c. FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF d.
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
16
Show abbreviations for the following
addresses a. 00000000FFFF00000000000000000
000 b. 12342346000000000000000000001111 c.
00000001000000000000000012001000 d.
00000000000000000000FFFF24.123.12.6
Solution a. 00FFFF b. 123423461111 c.
0112001000 d. FFFF24.123.12.6
17
Decompress the following addresses and show the
complete unabbreviated IPv6 address a.
11112222 b. c. 01 d.
AAAAAAA1234 Solution a. 11110000000000000
000000000002222 b. 00000000000000000000000
000000000 c. 0000000100000000000000000000
0000 d. AAAA000A00AA00000000000000001234
18
Address Space

• The address space of IPv6 contains 2128
  addresses. This address space is 296 times of the
  IPv4 address

19
To give some idea about the number of addresses,
let us assume that the number of people on the
planet earth is soon to be 234 (more than 16
billion). Each person can have 294 addresses to
use.
20
If we assign 260 addresses to the users each year
(almost one billion each second), it takes 268
years to deplete addresses.
21
Categories of Addresses

• IPv6 defines 3 types of addresses unicast,
  anycast, and multicast
• A unicast address defines a single computer. The
  packet sent to a unicast address must be
  delivered to that specific computer
• An anycast address defines a group of computers
  that all share a single address. A packet sent to
  an anycast address must be delivered to exactly
  one of the members of the groupthe closest or
  the most easily accessible. IPv6 does not
  designate a block for anycasting the addresses
  are assigned from the unicast block
• A multicast address defines a group of computers.
  A packet sent to a multicast address must be
  delivered to each member of the group

22
Address Space Allocation

• The address space is divided into several blocks
  of varying size and each block is allocated for
  special purpose
• To better understand the allocation and the
  location of each block in address space, the
  whole address space is divided into 8 equal
  regions
• Each section is 1/8 of the whole address space.
  The first section contains 6 variable-size
  blocks. The second section is considered one
  single block and is used for global unicast
  addresses. The next 5 sections are unassigned
  addresses. The last section is divided into 8
  blocks.

23
Prefixes for IPv6 Addresses
24
Figure 26.5 shows that only a portion of the
address space can be used for global unicast
communication. How many addresses are in this
block? Solution This block occupies only
one-eighth of the address spaces. To find the
number of addresses, we can divide the total
address space by 8 or 23 . The result is
(2128)/(23) 2125 a huge block.
25
Algorithm for finding the allocated blocks
26
Unspecified Address

• This is an address in which the entire address
  consists of zeros
• It is used during bootstrap when a host does not
  know its own address and sends an inquiry to find
  its address
• It cannot be used as a destination address
• The CIDR notation for this one-address subblock
  is /128

27
Comparing the unspecified address in IPv4 to the
unspecified addresses in IPv6. Solution In both
architectures, an unspecified address is an
all-zero address. In IPv4 this address is part of
class A address in IPv6 this address is part of
the reserved block.
28
Loopback Address

• This is an address used by a host to test itself
  without going into the network
• A message is created in the application layer,
  sent to the transport layer, and passed to the
  network layer
• It then returns to the transport layer and then
  passes to the application layer
• This is very useful for testing the functions of
  software packages in these layer before even
  connecting the computer to the network

29
Compare the loop addresses in IPv4 to the
loopback address in IPv6. Solution There are two
differences in this case. In classful addressing,
a whole block is allocated for loopback
addresses in IPv6 only one address is allocated
as the loopback address. In addition, the
loopback block in classful addressing is part of
the class A block. In IPv6, it is only one single
address in the reserved block.
30
IPv4 Compatible Addresses

• Addresses that use the prefix (00000000) are
  reserved, but part of it is used to define some
  IPv4 compatible addresses

31
Embedded IPv4 Addresses

• During transition from IPv4 to IPv6, hosts can
  use their IPv4 addresses embedded in IPv6
  addresses
• Two formats have been designed for this purpose
  compatible and mapped
• A compatible address is an address of 96 bits of
  zeros followed by 32 bits of IPv4 address
• It is used when a computer using IPv6 wants to
  send a message to another computer using IPv6
• However, suppose the packet passes through a
  region where the networks are still using IPv4

32
Embedded IPv4 Addresses (cont.)

• A mapped address comprises 80 bits of zero,
  followed by 16 bits of one, followed by the
  32-bit IPv4 address
• It is used when a computer that has migrated to
  IPv6 wants to send a packet to a computer still
  using IPv4
• The packet travels mostly through IPv6 networks
  but is finally delivered to a host that uses IPv4

33
Embedded IPv4 Addresses (cont.)

• A very interesting point about mapped and
  compatible addresses is that when calculating the
  checksum, one can use the embedded address or the
  total address because extra 0s or 1s in multiple
  of 16 dont have any effect in checksum
  calculation

34
Unique Local Unicast Block

• IPv6 uses two large blocks for private
  addressing one at the site level and one at the
  link level
• A subblock in a unique local unicast block can be
  privately created and used by a site
• The packet carrying this type of address as the
  destination address is not expected to be routed
• This type of address has the block identifier
  1111 110, the next bit can be 0 or 1 to define
  how the address is selected (locally or by an
  authority)
• The next 40 bits are selected by the site using a
  randomly generated of length 40 bits

35
Link Local Block

• The second block designed for private addresses
  is link local block
• A subblock in this block can be used as a private
  address in a network
• This type of address has the block identifier
  1111111010. The next 54 bits are set to zero. The
  last 64 bits can be changed to define the
  interface for each computer

36
Multicast Block

• In IPv6, multicast block uses the prefix
  11111111. The second field is a flag that defines
  the group address as either permanent or
  transient
• A permanent group address is defined by the
  Internet authorities and can be accesses at all
  times
• A transient group address is used only
  temporarily such as in a teleconference
• The third defines the scope of the group address

37
Global Unicast Address

• This block in the address space is used for
  unicast communication
• An address in this block is divided into 3 parts
  global routing prefix, subnet identifier, and
  interface identifier

38
Global Routing Prefix

• The first 48 bits of a global unicast address are
  called global routing prefix
• They are used to route packets through the
  Internet to the organization site such as ISP
• Since the first 3 bits is fixed (001), the rest
  of the 45 bits can define up to 245 sites (a
  private organization or an ISP)

39
Subnet Identifier

• The next 16 bits defines a subnet in an
  organization
• This means that an organization can have up to
  216 subnet, which is more than enough

40
Interface Identifier

• The last 64 bits define the interface identifier
  which is similar to hostid in IPv4 addressing
• In IPv4 addressing, there is not a specific
  relation between the hostid (at the IP level) and
  physical or MAC address (at the data link layer)
  because the physical address is normally much
  longer than the hostid
• The IPv6 addressing allows this opportunity. A
  physical address whole length is less than 64
  bits can be embedded as the whole or part of the
  interface identifier, eliminating the mapping
  process
• Two physical addressing scheme can be considered
  the 64-bit extended unique identifier (EUI-64)
  defined by IEEE and the 48-bit physical address
  defined by Ethernet

41
Mapping EUI-64

• To map a 64-bit physical address, the
  global/local bit of this format needs to be
  changed from 0 to 1 (local to global) to define
  an interface address

42
Mapping Ethernet MAC Address

• Mapping a 48-bit Ethernet address into a 64-bit
  interface identifier is more involved
• We need to change the local/global bit to 1 and
  insert an additional 16 bits
• The additional 16 bits are defined as 15 ones
  followed by one zero, or FFEE16

43
Find the interface identifier if the physical
address in the EUI is (F5-A9-23-EF-07-14-7A-D2)16
using the format we defined for Ethernet
addresses. Solution We only need to change the
seventh bit of the first octet from 0 to 1 and
change the format to colon hex notation. The
result is F7A923EF07147AD2.
44
Find the interface identifier if the Ethernet
physical address is (F5-A9-23-14-7A-D2)16 using
the format we defined for Ethernet
addresses. Solution We only need to change the
seventh bit of the first octet from 0 to 1,
insert two octet FFFE16 and change the format to
colon hex notation. The result is
F7A923FFFE147AD2 in colon hex.
45
An organization is assigned the block
200014562474/48. What is the CIDR notation for
the blocks in the first and second subnets in
this organization. Solution Theoretically, the
first and second subnets should use the block
with subnet identifier 000116 and 000216. This
means that the blocks are 2000145624740000/6
4 and 2000145624740001/64.
46
An organization is assigned the block
200014562474/48. What is the IPv6 address of an
interface in the third subnet if the IEEE
physical address of the computer is
(F5-A9-23-14-7A-D2)16. Solution The interface
identifier is F7A923FFFE147AD2 (see Example
26.12). If we add this identifier to the global
prefix and the subnet identifier, we get
47
26-4 AUTOCONFIGURATION
One of the interesting features of IPv6
addressing is the autoconfiguration of hosts. As
we discussed in IPv4, the host and routers are
originally configured manually by the network
manager. However, the Dynamic Host Configuration
Protocol, DHCP, can be used to allocate an IPv4
address to a host that joins the network. In
IPv6, DHCP protocol can still be used to allocate
an IPv6 address to a host, but a host can also
configure itself.
48
Process of Auto-configuration

1. The host first creates a link local address for
   itself. The result is a 128-bit link local
   address
2. The host then tests to see if this link local
   address is unique and not used by other hosts.
   The host sends a neighbor solicitation message
   and waits for neighbor advertisement message. If
   any host in the subnet is using this address, the
   process fails and the host cannot autoconfigure
   itself it needs to use other means such as DHCP
   for this purpose

49
Process of Auto-configuration (cont.)

1. If the uniqueness of the link local address is
   passed, the host stores this address as its
   link-local address (for private communication),
   but it still needs a global unicast address. The
   host then sends a router solicitation message to
   a local router. If there is a router running on
   the network, the host receives a router
   advertisement message that includes the global
   unicast prefix and subnet prefix that the host
   needs to add to its interface identifier to
   generate its global unicast address. If the
   router cannot help the host with the
   configuration, it informs the host in the router
   advertisement message (by setting a flag). The
   host then needs to use other means for
   configuration.

50
Assume a host with Ethernet address
(F5-A9-23-11-9B-E2)16 has joined the network.
What would be its global unicast address if the
global unicast prefix of the organization is
3A2112162165 and the subnet identifier is
A2451232. Solution The host first creates its
interface identifier as F7A923FFFE119BE2
using the Ethernet address read from its card.
The host then creates its link-local address as
51
Assuming that this address is unique, the host
sends a router solicitation message and receives
the router advertisement message that announces
the combination of global unicast prefix and the
subnet identifier as 3A2112162165A2451232.
The host then appends its interface identifier to
this prefix to find and store its global unicast
address as
52
Packet Format

• Each packet is composed of a mandatory base
  header followed by the payload
• The payload consists of 2 parts optional
  extension headers and data from an upper layer
• The base header occupies 40 bytes, whereas the
  extension headers and data from the upper layer
  contain up to 65,535 bytes of information

53
Base Header

• Version. The 4-bit field defines the version
  number of the IP. For IPv6, the value is 6
• Traffic class. The 8-bit field is used to
  distinguish different payloads with different
  delivery requirements. It replaces the service
  class field in IPv4
• Flow label. This 20-bit field is designed to
  provide special handling for a particular flow of
  data
• Payload length. The 2-byte payload length field
  defines the length of the IP datagram excluding
  the base header

54
Base Header (cont.)

• Next header. The 8-bit field defines the header
  that follows the base header in the datagram. The
  next header is either one of the optional
  extension header or the header of an encapsulated
  packet such as TCP and UDP. This field in version
  4 is called the protocol
• Hop limit. The 8-bit field serves the same
  purpose as the TTL field in IPv4
• Source address. This field identifies the
  original source of the datagram
• Destination address. This field usually
  identifies the final destination of the datagram.
  However, if source routing is used, this field
  contains the address of the next router

55
Next Header Codes
56
Traffic Class

• The traffic class field defines the priority of
  each packet with respect to other packets from
  the same source
• If one of two consecutive datagrams must be
  discarded due to congestion, the datagram with
  the lower packet priority will be discarded
• IPv6 divides traffic into 2 broad categories
  congestion-controlled and non-congestion-controlle
  d

57
Congestion-Controlled Traffic

• If a source adapts itself to traffic slowdown
  when there is congestion, the traffic is referred
  to as congestion-controlled traffic
• In congestion-controlled traffic, it is
  understood that packets may arrive delayed or
  even lost or received out of order
• Congestion-controlled data are assigned
  priorities from 0 to 7 (lowest to highest)
• The priority description are as follows

58
Congestion-Controlled Traffic (cont.)

• No specific traffic. The priority 0 is assigned
  to a packet when the process does not define a
  priority
• Background data. This group defines data that is
  usually delivered in the background. Delivery of
  the news is a good example
• Unattended data traffic. If the user is not
  waiting (attending) for the data to be received,
  the packet will be given a priority 2. Email
  belongs to this group
• Attended bulk data traffic. A protocol that
  transfer data while the user is waiting to
  receive the data is given a priority 4. FTP and
  HTTP belong to this group
• Interactive traffic. Protocols such as TELNET
  that need user interaction are assigned a
  priority 6
• Control traffic. Control traffic such as OSPF,
  RIP, and SNMP is given the highest priority

59
Noncongestion-Controlled Traffic

• This refers to a type of traffic that expects
  minimum delay. Discarding of packet is not
  desirable. Retransmission is most cases is
  impossible
• Real-time audio and video are example of this
  type of traffic
• Priority number from 8 to 15 are assigned to this
  type of traffic. The priorities are usually
  assigned based on how much the quality of
  received data is affected by discarding some
  packets
• Data containing less redundancy (such as
  low-fidelity audio or video) can be given a
  higher priority than data containing more
  redundancy (such as high-fidelity audio or video)

60
Flow Label

• To a router, a flow is a sequence of packets that
  share the same characteristics such as traveling
  the same path, using the same resources, having
  the same kind of security, and so on
• A router that supports the handling of flow
  labels has a flow label table. The table has an
  entry for each active flow label each entry
  defines the services required by the
  corresponding flow label
• When the router receives a packet, it consults
  its flow label table to find the corresponding
  entry for the flow label value defined in the
  packet. It then provides the packet with the
  service mentioned in the entry

61
Flow Label (cont.)

• However, the flow label itself does not provide
  the information for the entries of the flow label
  table the information is provided by other means
  such as the hop-by-hop options or other protocols
• In its simplest form, a flow label can be used to
  speed up the processing of a packet by a router.
  When a router receives a packet, instead of
  consulting the routing table, it can easily look
  in a flow label for the next hop

62
Flow Label (cont.)

• In its more sophisticated form, a flow label can
  be used to support the transmission of real-time
  audio and video
• A process can make a reservation for these
  resources beforehand to guarantee that real-time
  data will not be delayed due to a lack of
  resources

63
Flow Label (cont.)

• To allow the effective use of flow labels, 3
  rules have been defined
• The flow label is assigned to a packet by the
  source host. The label is a random number between
  1 and 224-1
• If a host does not support the flow label, it
  sets this field to zero. If a router does not
  support the flow label, it simply ignores it
• All packets belonging to the same flow have the
  same source, same destination, same priority, and
  same options

64
Comparison between IPv4 and IPv6 Headers
65
Extension Headers

• To give more functionality to the IP datagram,
  the base header can be followed by up to six
  extension headers which are hop-by-hop option,
  destination option, source routing,
  fragmentation, authentication, and encrypted
  security payload

66
Extension Header Format
67
Hop-by-Hop Option

• The hop-by-hop option is used when the source
  needs to pass information to all routers visited
  by the datagram
• The first field defines the next header in the
  chain of headers
• The header length defines the number of bytes in
  the header (including the next header field).
• The rest of the header contains different options

68
Hop-by-Hop Option (cont.)

• So far, only three options have been defined
  Pad1, PadN and jumbo payload
• Pad1 and PadN are designed for alignment purposes
• Jumbo payload is used to define a longer length
  than the maximum length of 65,535 bytes

69
Pad1

• This option is 1 byte long and is designed for
  alignment purposes
• Some options need to start at a specific bit of
  the 32-bit word. If an option falls short of this
  requirement by exactly one byte, Pad1 is added to
  make up the difference
• Pad1 contains neither the option length field nor
  the option data field. It consists solely of the
  option code field with all bits set to 0
• Pad1 can be inserted anywhere in the hop-by-hop
  option header

70
PadN

• PadN is similar in concept to Pad1. The
  difference is that PadN is used with 2 or more
  bytes are needed for alignment
• This option consists of 1 byte of option code, 1
  byte of option length, and a variable number of
  zero padding bytes
• The value of the option code is 1 (action is 00,
  the change bit is 0, and type is 00001)
• The option length contains the number of padding
  bytes

71
Jumbo Payload

• Jumbo payload option is used to define the longer
  length of the maximum IP packet size
• The jumbo payload option must always start at a
  multiple of 4 bytes plus 2 from the beginning of
  the extension headers

72
Destination Option

• The destination option is used when the source
  needs to pass information to the destination only
• Intermediate routers are not permitted access to
  this information
• The format of the destination option is the same
  as the hop-by-hop option
• So far, only the Pad1 and PadN options have been
  defined

73
Source Routing

• The source routing extension header combines the
  concepts of the strict source route and the loose
  source route options of IPv4
• The source routing header contains a minimum of 7
  field. The first 2 fields are identical to that
  of the hop-by-hop extension header
• The type field defines source routing type
• The address left field indicates the number of
  hops still needed to reach the destination
• The strict/loose mask field determines by the
  source. If the mask is loose, other routers may
  be visited in addition to those in the header

74
Source Routing Example
75
Fragmentation

• In IPv4, the source or a router is required to
  fragment if the size of the datagram is larger
  than the MTU of the network over which the
  datagram travels
• In IPv6, only the original source can fragment. A
  source then must use a Path MTU Discovery
  technique to find the smallest MTU supported by
  any network on the path
• If the source does not use a Path MTU Discovery
  technique, it fragments the datagram to a size of
  1280 bytes or smaller

76
Authentication

• The authentication extension header has a dual
  purpose it validates the message sender and
  ensures the integrity of data
• The former is needed so the receiver can be sure
  that a message is from the genuine sender and not
  from an imposter
• The latter is needed to check that the data is
  not altered in transition by some hacker
• The security parameter index field defines the
  algorithm used for authentication
• The authentication data field contains the actual
  data generated by the algorithm

77
Encrypted Security Payload

• The encrypted security payload (ESP) is an
  extension confidentiality and guards against
  eavesdropping
• The parameter index field is a 32-bit word that
  defines the type of encryption/decryption used
• The other field contains the encrypted data along
  with any extra parameters needed by the algorithm
• Encryption can be implemented in 2 ways
  transport mode or tunnel mode (discussed in IPSec
  chapter)

78
Options Comparison between IPv4 and IPv6
79
Transition From IPv4 To IPv6

• It takes a considerable amount of time before
  every system in the Internet can move from IPv4
  and IPv6
• The transition must be smooth to prevent any
  problems between IPv4 and IPv6 systems
• Three strategies have been devised by the IETF to
  help the transition dual stack, tunneling,
  header translation

80
Dual Stack

• It is recommended that all hosts, before
  migrating completely to version 6, have a dual
  stack of protocol
• To determine which version to use when sending a
  packet to a destination, the source host queries
  the DNS

81
Tunneling

• Tunneling is a strategy used when 2 computers
  using IPv6 want to communicate with each other
  and the packet must pass through a region that
  uses IPv4
• The IPv6 packet is encapsulated in a IPv4 packet
  when it enters the region and it leaves its
  capsule when it exits the region
• To make it clear that the IPv4 packet is carrying
  an IPv6 packet as data, the protocol value is set
  to 41
• Tunneling uses the compatible addresses

82
Automatic Tunneling

• If the receiving host uses a compatible IPv6
  address, tunneling occurs automatically without
  any reconfiguration
• In automatic tunneling, the sender sends the
  receiver an IPv6 packet using the IPv6 compatible
  address as the destination address
• When the packet reaches the boundary of the IPv4
  network, the router encapsulates it in an IPv4
  packet, which should have an IPv4 address
• To get this address, the router extracts the IPv4
  address embedded in the IPv6 address
• The packet then travels the rest of its journey
  as an IPv4 packet

83
Configured Tunneling

• If the receiving host does not support an
  IPv6-compatible address, the sender receives a
  noncompatible IPv6 address from the DNS
• In this case, configured tunneling is used. The
  sender sends the IPv6 packet with the receivers
  noncompatible IPv6 address
• However, the packet cannot pass through the IPv4
  region without first being encapsulated in an
  IPv4 packet
• The 2 routers at the boundary of the IPv4 region
  are configured to pass the packet encapsulated in
  an IPv4 packet

84
Configured Tunneling (cont.)

• The router at one end sends the IPv4 packet with
  its own IPv4 address as the source and the other
  routers IPv4 address as the destination
• The other router receives the packet,
  decapsulates the IPv6 packet, and sends it to the
  destination host

85
Header Translation

• Header translation is necessary when the majority
  of the Internet has moved to IPv6 but some system
  still use IPv4
• Tunneling does not work in this situation because
  the packet must be in the IPv4 format to be
  understood by the receiver
• In this case, the header format must be changed
  totally through header translation
• Header translation uses the mapped address to
  translate an IPv6 address to an IPv4 address

86
Header Translation Procedure