This document provides an overview of IPv6 addressing and connectivity. It describes the various types of IPv6 addresses including global aggregateable unicast addresses, site-local addresses, unique local addresses, and link-local addresses. It also covers IPv6 address formats and special addresses like the unspecified, loopback, multicast, and solicited node multicast addresses. Transition mechanisms from IPv4 to IPv6 are also briefly mentioned.

1. IPv6 Notes from
IP Addressing and Basic Connectivity
and
TCP/IP Tutorial and
Technical Overview

2. Implementing IPv6 Addressing and Basic
Connectivity
• IPv6, formerly named IPng (next generation),
is the latest version of the Internet Protocol
(IP). IP is a packet-based protocol used to
exchange data, voice, and video traffic over
digital networks.

3. Implementing IPv6 Addressing and Basic
Connectivity
• IPv6 quadruples the number of network
address bits from 32 bits (in IPv4) to 128 bits.
• By being globally unique, IPv6 addresses
inherently enable global reachibility and end-
to-end security for networked devices.

4. IPv6 Addressing and Basic
Connectivity
• The flexibility of the IPv6 address space
reduces the need for private addresses and
the use of Network Address Translation
(NAT) thus, IPv6 enables new application
protocols that do not require special
processing by border routers at the edge of
networks.

5. IPv6 Address Formats
• IPv6 addresses are represented as eight
groups of four hexadecimal digits separated
by colons (:) in the format:
• 2001:0DB8:7654:3210:FEDC:BA98:7654:3210
• 2001:0DB8:0:0:8:800:200C:417A

6. IPv6 Address Formats
• It is common for IPv6 addresses to contain
successive hexadecimal fields of zeros.
• To make IPv6 addresses less cumbersome,
two colons (::) may be used to compress
successive hexadecimal fields of zeros at the
beginning, middle, or end of an IPv6 address.
• Two colons (::) can be used only once in an
IPv6 address, to represent the longest
successive hexadecimal fields of zeros.

7. IPv6 Special Addresses
IANA maintains the official list of the IPv6 address space. Global
unicast assignments can be found at the various RIRs or at the
GRH DFP pages.
There are a number of addresses with special meaning in IPv6:
Unspecified address
::/128 — the address with all zero bits is called the unspecified
address. This address must never be assigned to an interface and
is to be used only in software before the application has learned
its host's source address appropriate for a pending connection.
Routers must not forward packets with the unspecified address.
Link local addresses
::1/128 — the loopback address is a unicast local host address. If an
application in a host sends packets to this address, the IPv6 stack
will loop these packets back on the same virtual interface
(corresponding to 127.0.0.1 in IPv4).
fe80::/10 — The link-local prefix specifies that the address is only
valid on a single link. This is analogous to the autoconfiguration IP
addresses 169.254.0.0/16 in IPv4.

8. IPv6 Special Addresses
Unique local addresses
• fc00::/7 — unique local addresses (ULA) are routable only
within a set of cooperating sites. They were defined in RFC
4193 as a replacement for site-local addresses (see below). The
addresses include a 40-bit pseudorandom number in the
routing prefix that intends to minimize the risk of conflicts if
sites merge or packets are misrouted into the Internet. Despite
the restricted, local usage of these addresses, their address
scope is global. This is a departure from the prior definitions of
site-local addresses.
Multicast addresses
• ff00::/8 — The multicast prefix designates multicast addresses
as defined in "IP Version 6 Addressing Architecture" (RFC
4291). Some of these have been assigned to specific protocols,
for example ff02::101 will reach all link-local NTP servers (RFC
2375).
Solicited-node multicast addresses
• ff02::1:FFXX:XXXX — XX:XXXX are the 3 low order octets of the
corresponding unicast or anycast address.

9. IPv6 Special Addresses
• IPv4 transition
::ffff:0:0/96 — this prefix is used for IPv4 mapped addresses
2001::/32 — Used for Teredo tunneling.
2002::/16 — this prefix is used for 6 to 4 addressing.
• ORCHID
2001:10::/28 — ORCHID (Overlay Routable Cryptographic
Hash
Identifiers) as per (RFC 4843). These are non-routed IPv6
addresses used for Cryptographic Hash Identifiers.
• Documentation
2001:db8::/32 — this prefix is used in documentation (RFC
3849). The addresses should be used anywhere an example
IPv6 address is given or model networking scenarios are
described.

10. IPv6 Special Addresses
• Deprecated or obsolete addresses
::/96 — This is a 96-bit zero-value prefix originally known as IPv4-
compatible addresses. This class of addresses were used to
represent IPv4 addresses within an IPv6 transition technology.
Such an IPv6 address has its first 96 bits set to zero, while its
last 32 bits are the IPv4 address that is represented. The
Internet Engineering Task Force (IETF) has deprecated the use
of IPv4-compatible addresses with publication RFC 4291. The
only remaining use of this address format is to represent an
IPv4 address in a table or database with fixed size members
that must also be able to store an IPv6 address.
fec0::/10 — The site-local prefix specifies that the address is valid
only within the site network of an organization. Its use has
been deprecated in September 2004 by RFC 3879 and new
systems must not support this special type of address. New
specifications replace this address type with unique local
addresses.

11. IPv6 Address Type: Unicast
• An IPv6 unicast address is an address destined for
a single interface, on a single node.
• A packet that is sent to a unicast address is
delivered to the interface identified by that address.
• Cisco IOS software supports the following IPv6
unicast address types:
Aggregateable Global Address
Site-Local Address
Unique-Local Address
Link-Local Address

12. Global Aggregateable Unicast Address
• A global unique address is an IPv6 address that’s
routable on the internet and may be aggregated
upwards through organizations, and eventually to
the Internet Service Providers (ISPs).
• Addresses with a prefix of 2000::/3 (001) through
E000::/3 (111) are required to have 64-bit interface
identifiers in the Modified (EUI)-64 format.
• The Internet Assigned Numbers Authority (IANA)
allocates the IPv6 address space in the range of
2000::/16 to regional registries.

13. Modified EUI-64 Interface ID

14. Global Aggregateable Unicast Address
The Global Unicast Address consists of a:
• 48-bit global routing prefix: which included the Top-Level
Aggregator (TLA) and Next-Level Aggregator (NLA) but
because they were policy-based they were removed)
•16-bit subnet ID: (Site-Level Aggregator) used by individual
organizations to create their own local addressing hierarchy
and identify subnets (as in IPv4). An organization with an IPv6
subnet ID can support up to 65,535 individual subnets.
•Interface-ID: used to identify interfaces on a link, the interface
ID must be unique to the link. Interface IDs used in global
unicast and other IPv6 address types must be 64 bits long and
constructed in the modified EUI-64 format.

15. Site-Local address
• A site-local address is an IPv6 unicast address that
uses the prefix FEC0::/10, and concatenates the
subnet identifier (16-bit SLA field) with the interface
identifier in the modified EUI-64 format.
• Site-local addresses can be used to number a
complete site without using a globally unique prefix.
• Site-local addresses can be considered private
addresses because they can be used to restrict
communication to a limited domain.
• IPv6 routers must not forward packets that have site-
local source or destination addresses outside of the
site.
• Site-local addresses are being obsolecesed by
Unique-local addresses, though some still exist.

16. Site-Local address

17. Unique Local Address
• A unique local address is an IPv6 unicast address with a prefix
FC00::/7 or FD00::/7, that’s globally unique, and intended for local
communications. They are not expected to be routable on the global
Internet and are routable inside of a limited area, such as a site.
• A unique local address has:
• It has a well-known, globally unique prefix to allow for
easy filtering at site boundaries.
• It allows sites to be combined or privately interconnected
without creating any address conflicts or requiring
renumbering of interfaces that use these prefixes.
• It is ISP-independent and can be used for communications
inside of a site without having any permanent or intermittent
Internet connectivity.
• If it is accidentally leaked outside of a site via routing or
DNS, there is no conflict with any other addresses.
• Applications may treat unique local addresses like global
scoped addresses.

18. Unique Local Address

19. Link-Local Address
• A link-local address is an IPv6 unicast address that
can be automatically configured on any interface
• It Uses the link-local prefix FE80::/10 (1111 1110 10)
and the interface identifier in modified EUI-64format.
• Link-local addresses are used in the neighbor
discovery protocol and the stateless auto-
configuration process.
• Nodes on a local link can use link-local addresses to
communicate; the nodes do not need site-local or
globally unique addresses to communicate.
• IPv6 routers must not forward packets that have link-
local source or destination addresses to other links.

20. Link-Local Address

21. Internet transition: Migrating IPv4 to IPv6
• If the Internet is to realize the benefits of IPv6, a
period of transition will be necessary when new IPv6
hosts and routers are deployed alongside existing
IPv4 systems.
• RFC 2893 (Transition Mechanisms for IPv6 Hosts
and Routers) and RFC2185 (Routing Aspects of IPv6
Transition), define a number of mechanisms to
ensure both the compatibility between old and new
systems and a gradual transition that doesn’t impact
functionality of the Internet.
• These techniques are sometimes collectively termed
Simple Internet Transition (SIT).

22. IPv4/IPv6 Transitional addresses
The transition employs the following techniques:
• Dual-stack IP implementations for hosts and routers
that must interoperate between IPv4 and IPv6.
• IPv6-over-IPv4 tunneling mechanisms for carrying
IPv6 packets across IPv4 router networks.
• IPv4/IPv6 header translation. This technique is
intended for use when implementation of IPv6 is well
advanced and only a few IPv4-only systems remain.
• Embedding of IPv4 addresses in IPv6 addresses.
IPv6 hosts will be assigned addresses that are
interoperable with IPv4, and IPv4 host addresses will
be mapped to IPv6.

23. IPv4/IPv6 Compatible addresses
• An IPv4-compatible IPv6 address is an IPv6 unicast
address that has zeros in the high-order 96 bits, and
an IPv4 address in the low-order 32 bits of the
address.
• The format: 0:0:0:0:0:0:192.0.2.128 or ::192.0.2.128
• The IPv6 address of a node is the entire 128-bit IPv4-
compatible IPv6 address with embedded IPv4
address and the IPv4 address of the node is the low-
order 32 bits from the 128 bit address.
• IPv4-compatible IPv6 addresses are assigned to
nodes that support both IPv4 and IPv6 protocol
stacks and are used in automatic tunnels.
80 bits 16 bits 32 bits
zeros 0000(=96) 192.0.2.128

24. IPv6/IPv4 Mapped addresses
• Dual stack IPv6/IPv4 implementations typically
support a special class of addresses, the IPv4
mapped addresses.
• This address type has its first 80 bits set to zero, the
next 16 set to one (FFFF), while its last 32 bits
represent an IPv4 address.
• For example, ::ffff:c000:280(all hex) is the IPv4
mapped address for the IPv4 address 192.0.2.128.

25. IPv4 Mapped addresses cont.
As an exception to standard IPv6 address notation
(all hex),
IPv4 mapped addresses are commonly represented
with their last 32 bits written in dot-decimal notation
(eg. IPv4), appended to the standard IPv6 notation of
the leading bits, e.g. ::ffff:c000:280 could be written
as ::ffff:192.0.2.128.
80 bits 16 bits 32 bits
zeros FFFF 192.0.2.128

26. IPv4 Mapped addresses cont.
• This address type allows the transparent use of the
transport layer protocols over IPv4 through the IPv6
networking API.
• A benefit of this mechanism is that server
applications only need to open a single listening
socket to handle connections from clients using
IPv6 or IPv4 protocols.
• IPv6 clients will be handled natively by default, and
IPv4 clients appear as IPv6 clients with an
appropriately mapped address.
• It can also be used to establish IPv4 connections
specifically with an IPv6 socket. While the network
protocol on the transmission medium is IPv4, the
connection is presented as an IPv6 interface to the
application.

27. IPv6 Address Type: Anycast
• An Anycast address is an address that is assigned
to a set of interfaces that typically belong to different
routers.
• A packet sent to an anycast address is delivered to
the closest interface as defined by the routing
protocols in use.
• Anycast addresses are syntactically the same as
unicast addresses since they’re allocated from the
unicast address space.
• Routers to which the anycast address are assigned
must be explicitly configured to recognize that the
address is an anycast address.

28. IPv6 Address Type: Anycast
• Anycast addresses can be used only
by a router, not a host, and anycast
addresses must not be used as the
source address of an IPv6 packet.

29. IPv6 Address Type: Multicast
• An IPv6 multicast address is an IPv6 address
that has a prefix of FF00::/8 (1111 1111).
• An IPv6 multicast address is an identifier for
a set of interfaces that typically belong to
different nodes.
• A packet sent to a multicast address is
delivered to all interfaces identified by the
multicast address.

30. IPv6 Address Type: Multicast
• The second octet following the prefix defines the
lifetime and scope of the multicast address.
• A permanent multicast address has a lifetime
parameter equal to 0.
• A temporary multicast address has a lifetime
parameter equal to 1.
• A multicast address that has the scope of a node,
link, site, or organization, or a global scope has a
scope parameter of 1, 2, 5, 8, or E, respectively.
For example, a multicast address with the prefix FF02::/16 is a
permanent multicast address with a link scope.

31. IPv6 Address Type: Multicast

32. IPv6 Multicast Groups
Group ID (Interface Id, above slide) Identifies the multicast group. Some
special purpose multicast addresses are predefined as follows:
FF01::1 All interfaces node-local. All interfaces on the host itself.
FF02::1 All nodes link-local. All systems on the local network.
FF01::2 All routers node-local. All routers local to the host itself.
FF02::2 All routers link-local. All routers on the same link as the
host.
FF05::2 All routers site-local. All routers on the same site as the host.
FF02::B Mobile agents link-local.
FF02::1:2 All DHCP agents link-local.
FF05::1:3 All DHCP servers site-local.

33. IPv6 Multicast Groups
• A special multicast address, the solicited node
multicast address, is used by ICMP for neighbor
discovery and duplicate address detection. It has
the format:
• FF02::1:FFxx:xxxx, where xx xxxx is taken from the
last 24-bits of a nodes unicast address.
• A node’s IPv6 address of 4025::01:800:100F:7B5B
belongs to the multicast group FF02::1:FF0F:7B5B.
• For a more complete listing of reserved multicast
addresses, see the IANA documentation– IPv6
Multicast Addresses Assignments.

34. IPv6 Header Format
• The basic IPv6 packet header has 8 fields with a total
size of 40 octets. Fields were removed from the IPv6
header because, in IPv6, fragmentation is not
handled by routers and checksums at the network
layer are not used.
• Instead, fragmentation in IPv6 is handled by the
source of a packet and checksums at the data link
layer and transport layer are used.
• In IPv4, the User Datagram Protocol transport layer
uses an optional checksum. In IPv6, use of the UDP
checksum is required to check the integrity of the
inner packet.
• Additionally, the basic IPv6 packet header and
options field are aligned to 64 bits, which can
facilitate the processing of IPv6 packets.

35. IPv6 Basic IP Header

36. IPv6 Basic Packet Header
Version Similar to the Version field in the IPv4 packet header, except that the field lists
number 6 for IPv6 instead of number 4 for IPv4.
Traffic Class Similar to the Type of Service field in the IPv4 packet header. The Traffic Class
field tags packets with a traffic class that is used in differentiated services.
Flow Label A new field in the IPv6 packet header. The Flow Label field tags packets with a
specific flow that differentiates the packets at the network layer.
Payload Similar to the Total Length field in the IPv4 packet header. The Payload Length
Length field indicates the total length of the data portion of the packet.
Next Header Similar to the Protocol field in the IPv4 packet header. The Next Header field
determines the type of information following the basic IPv6 header. The type of
information following the basic IPv6 header can be a transport-layer packet, for
example, a TCP or UDP packet, or an Extension Header,
Hop Limit Similar to the Time to Live field in the IPv4 packet header. The value of the Hop
Limit field specifies the maximum number of routers that an IPv6 packet can
pass through before the packet is considered invalid. Each router decrements
the value by one. Because no checksum is in the IPv6 header, the router can
decrement the value without needing to recalculate the checksum, which saves
processing resources.
Source & Similar to the Source & Destination fields in the IPv4 header, except that the
Dest. Address field
contains a 128-bit address for IPv6, instead of a 32-bit source address for IPv4.

37. IPv6 Extension Headers

38. IPv6 Extension Headers
Hop by Hop Options 0 This header is processed by all hops in the path of a packet. When
present, and always follows immediately after the basic IPv6 packet
header.
Destination options 60 Is processed at the final destination and also at each visited address
header specified by a routing header when followed by the hop-by-hop options
header. Alternatively, the destination options header can follow any
Encapsulating Security Payload (ESP) header, in which case the
destination options header is processed only at the final destination.
Routing header 43 The routing header is used for source routing.
Fragment header 44 Used when a source must fragment a packet that is larger than the MTU for
the path between itself and a destination. Used in each fragmented packet.
Authentication header 51 The Authentication header and the ESP header are used within IP Security
and Protocol (IPSec) to provide authentication, integrity, and confidentiality of a
ESP header 50 packet. These headers are identical for both IPv4 and IPv6.
Transport (upper-layer) 6 TCP The Upper-layer headers are the typical transport-layer headers used inside
headers a packet to transport the data. The two main transport protocols are TCP and
UDP.
17 UDP
Mobility header 135 Extension headers used by mobile nodes, correspondent nodes, and home
agents in all messaging related to the creation and management of bindings.

39. Unicast Reverse Path Forwarding
• The Unicast RPF feature is invoked to mitigate problems
caused by malformed or forged (spoofed) IPv6 source
addresses that pass through an IPv6 router.
• Malformed or forged source addresses can indicate denial-of-
service (DoS) attacks based on source IPv6 address spoofing.
• Unicast RPF checks to see if any packet received at a router
interface arrives on one of the best return paths to the source
of the packet. Unicast RPF does this by doing a reverse lookup
in the CEF table.
• With Unicast RPF, all equal-cost “best” return paths are
considered valid. Unicast RPF works in cases where multiple
return paths exist provided that each path is equal to the
others in terms of the routing cost (number of hops, weights,
and so on) and as long as the route is in the FIB.

40. Unicast Reverse Path Forwarding
• Where NOT to use Unicast RPF.
• Unicast RPF should not be used where UPSR ring topologies
are implemented such as within the core of an ISP, or on
interfaces that are internal to the network. These interfaces are
likely to have routing asymmetry meaning the number of hops
in the transmit and receive path differ. Unicast RPF should be
applied only where there is natural or configured symmetry. As
long as administrators carefully plan which interfaces they
activate Unicast RPF on, routing asymmetry is not a serious
problem.
• Routers at the edge of the network of an ISP are more likely to
have symmetrical reverse paths than routers that are in the
core of the ISP network.
• Routers that are in the core of the ISP network have no
guarantee that the best forwarding path out of the router will be
the path selected for packets returning to the router. Hence, it
is not recommended that you apply Unicast RPF where there is
a chance of asymmetric routing. It is simplest to place Unicast
RPF only at the edge of a network or, for an ISP, at the
customer edge of the network.

41. Unicast Reverse Path Forwarding
Unicast RPF Blocking Traffic in an Asymmetrical Routing Environment

42. Path MTU Discovery for IPv6
• As in IPv4, path MTU discovery in IPv6 allows a host
to dynamically discover and adjust to differences in
the MTU size of every link along a given data path.
• In IPv6, however, fragmentation is handled by the
source of a packet when the path MTU of one link
along a given data path is not large enough to
accommodate the size of the packets.
• Having IPv6 hosts handle packet fragmentation
saves IPv6 router processing resources and helps
IPv6 networks run more efficiently.
• In IPv6, the minimum link MTU is 1280 octets. We
recommend using an MTU value of 1500 octets for
IPv6 links.

43. IPv6 Neighbor Discovery
• Neighbor discovery is a function that enables a node
to identify other hosts and routers on its links.
• The node needs to know of at least one router so
that it knows where to forward packets if a target
node is not on its local link.
• Neighbor discovery also allows a router to redirect a
node to use a more appropriate router if the node
has initially made an incorrect choice.
• There are two ways that neighbor discovery are
performed in IPv6. Statelessly via ICMPv6 and
Statefuly via DHCPv6

44. IPv6 Neighbor Discovery
• An IP address is obtained statefuly (DHCPv6) or
Statelessly (ICMPv6)
• The M bit in an RA message determines how the IP
address is obtained.
• The O bit determines if other configuration
parameters are configured statefuly as well.
• An IP address is obtained statefuly (DHCPv6) if the
M bit is set (1).
• An IP address is obtained Statelessly (ICMPv6) if the
M bit is not set (0).

45. Internet Control Message Protocol Version 6
(ICMPv6)
• In order for IP to move data from one node to another
successfully, there are many functions that need to be carried
out, (error reporting, route discovery, and diagnostics) to name
a few. These tasks are carried out by Internet Control Message
Protocol
• ICMPv6 also carries out the tasks of conveying multicast group
membership information, (a function that was previously
performed by the IGMP protocol in IPv4), and address
resolution, (previously performed by ARP).
• ICMPv6 messages and their use are specified in RFC 4443 –
Internet Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) and RFC 2461 – Neighbor Discovery
for IP Version 6 (IPv6). Both RFCs are draft standards with a
status of elective.
• Every ICMPv6 message is preceded by an IPv6 header (and
possibly some IP extension headers). The ICMPv6 header is
identified by a Next Header value of 58 in the immediately
preceding header.

46. Internet Control Message Protocol Version 6
(ICMPv6)
There are two classes of ICMPv6 messages.
Error messages Type 0 to 127.
Informational messages Type 128 to 255.

47. Internet Control Message Protocol Version 6
(ICMPv6)
ICMPv6 message types include:
1 Destination Unreachable
2 Packet Too Big
3 Time (Hop Count) Exceeded
4 Parameter Problem
128 Echo Request
129 Echo Reply
130 Group Membership Query
131 Group Membership Report
132 Group Membership Reduction
133 Router Solicitation
134 Router Advertisement
135 Neighbor Solicitation
136 Neighbor Advertisement
137 Redirect Message

48. IPv6 Neighbor Discovery Messages
• Type 133 Router Solicitation Message
• Type 134 Router Advertisement Message
• Type 135 Neighbor Solicitation Message
• Type 136 Neighbor Advertisement Message
• Type 137 Neighbor Redirect Message

49. IPv6 Neighbor Solicitation Message
• When a node wants to determine the link-layer address of
another node, the source address in a neighbor solicitation
message is the IPv6 address of the node sending the neighbor
solicitation message (Type 135).
• The destination address in the neighbor solicitation message is
the solicited-node multicast address that corresponds to the
IPv6 address of the destination node.
• The neighbor solicitation message also includes the link-layer
address of the source node.
• Neighbor solicitation messages are also used to verify the
reachability of a neighbor after the link-layer address of a
neighbor is identified.
• When a node wants to verify the reachability of a neighbor, the
destination address in a neighbor solicitation message is the
unicast address of the neighbor.

50. IPv6 Neighbor Solicitation Message

51. IPv6 Neighbor Solicitation Message

52. IPv6 Neighbor Advertisement Message
• After receiving the neighbor solicitation message, the
destination node replies by sending a neighbor advertisement
message, (Type 136) in the Type field of the ICMP packet
header, on the local link.
• The source address in the neighbor advertisement message is
the IPv6 address of the node interface sending the neighbor
advertisement message.
• The destination address in the neighbor advertisement
message is the IPv6 address of the node that sent the neighbor
solicitation message.
• The data portion of the neighbor advertisement message
includes the link-layer address of the node sending the
neighbor advertisement message.
• Neighbor advertisement messages are also sent when there is
a change in the link-layer address of a node on a local link.
• When there is such a change, the destination address for the
neighbor advertisement is the all-nodes multicast address.

53. IPv6 Neighbor Advertisement Message

54. IPv6 Neighbor Advertisement Message

55. IPv6 Router Advertisement Message
• Router advertisement (RA) messages, have a value
of 134 in the Type field of the ICMP packet header,
are periodically sent out each configured interface of
an IPv6 router.
• For stateless autoconfiguration to work properly, the
advertised prefix length in RA messages must
always be 64 bits.
• The RA messages are sent to the all-nodes multicast
address.

56. IPv6 Router Advertisement Message

57. IPv6 Router Advertisement Message

58. IPv6 Router Solicitation Message
• Router solicitation messages, value of Type 133 of
the ICMP packet header, are sent by hosts at system
startup so that the host can immediately
autoconfigure without needing to wait for the next
scheduled RA message.
• Router solicitation messages are usually sent by
hosts at system startup (the host does not have a
configured unicast address), the source address in
router solicitation messages is usually the
unspecified IPv6 address (0:0:0:0:0:0:0:0).
• RAs are also sent in response to router solicitation
messages.

59. IPv6 Router Solicitation Message

60. IPv6 Neighbor Redirect Message
• Routers send neighbor redirect messages to inform
hosts of better first-hop nodes on the path to a
destination.
• A value of 137 in the Type field of the ICMP packet
header identifies an IPv6 neighbor redirect message.
• A router must be able to determine the link-local
address for each of its neighboring routers in order
to ensure that the target address in a redirect
message identifies the neighbor router by its link-
local address.
• For static routing, the address of the next-hop router
should be specified using the link-local address of
the router.
• For dynamic routing, all IPv6 routing protocols must
exchange the link-local addresses of neighboring
routers.

61. IPv6 Neighbor Redirect Message

62. IPv6 Neighbor Redirect Message

63. IPv6 Stateless Auto-configuration
• A node on the link can automatically configure site-
local and global IPv6 addresses by appending its 64
bit interface ID to the 64 bit prefixes included in the
RA messages.
• The resulting 128-bit IPv6 addresses configured by
the node are then subjected to duplicate address
detection to ensure their uniqueness on the link.
• If the prefixes advertised in the RA messages are
globally unique, then the IPv6 addresses configured
by the node are also guaranteed to be globally
unique.
• Router solicitation messages, which have a value of
133 in the Type field of the ICMP packet header, are
sent by hosts at system startup so that the host can
immediately autoconfigure without needing to wait
for the next scheduled RA message.

64. IPv6 Stateless Auto-configuration

65. DHCP for IPv6 Prefix Delegation
• DHCP for IPv6 can be used in environments to
deliver statefull and stateless information.
• Again the M bit allows the IP address to be obtained
statefully when set (1) and statelessly when not (0)
• Other configuration parameters can be obtained
statefully via the O bit when set (1).
• For further information about this feature, see the
Implementing DHCP for IPv6 module in the Cisco
IOS IPv6 Configuration Library.

66. IPv6 Prefix Aggregation
• The aggregatable nature of the IPv6 address
space enables an IPv6 addressing hierarchy.
• An enterprise can subdivide a single IPv6
prefix from a service provider into multiple,
longer prefixes for use within its internal
network.
• Conversely, a service provider can aggregate
all of the prefixes of its customers into a
single, shorter prefix that the service
provider can then advertise over the IPv6
internet.
(see Figure 17)

67. IPv6 Prefix Aggregation

68. IPv6 Site Multi-homing
• Multiple IPv6 prefixes can be assigned to
networks and hosts.
• Having multiple prefixes assigned to a
network makes it easy for that network to
connect to multiple ISPs without breaking
the global routing table.
(see Figure 18)

69. IPv6 Site Multi-homing

70. Dual IPv4 and IPv6 Protocol Stacks
• The Dual IPv4 and IPv6 protocol stack technique can
be used to transition to IPv6 by enabling gradual
one-by-one upgrades to applications running on
nodes.
• Applications running on nodes are upgraded to
make use of the IPv6 protocol stack.
• Applications that are not upgraded, support only the
IPv4 coexisting with upgraded applications on a
node.
• New and upgraded applications make use of both
the IPv4 and IPv6 protocol stacks.
(see Figure 19).

71. Dual IPv4 and IPv6 Protocol Stacks

72. Dual IPv4 and IPv6 Protocol Stacks