computer networking

1. Chapter 7: Introduction to IPv6
Introduction:
IPv6 is an Internet Layer protocol for packet-switched internetworking and
provides end-to-end datagram transmission across multiple IP networks, closely
adhering to the design principles developed in the previous version of the
protocol, Internet Protocol Version 4 (IPv4). IPv6 was first formally described
in Internet standard document published in December 1998. In addition to
offering more addresses, IPv6 also implements features not present in IPv4. It
simplifies aspects of address assignment (stateless address autoconfiguration),
network renumbering and router announcements when changing network
connectivity providers. It simplifies processing of packets by routers by placing
the need for packet fragmentation into the end points.
IPv6 does not specify interoperability features with IPv4, but essentially creates
a parallel, independent network. Exchanging traffic between the two networks
requires translator gateways employing one of several transition mechanisms,
such as NAT64, the tunneling protocols 6to4, 6in4, Teredo.
Origination of IPv6:
Its main purpose of origination is the insufficiency of the IPv4 technology.
IPv4 included an addressing system that used numerical identifiers consisting of
32 bits. These addresses are typically displayed in quad-dotted notation as
decimal values of four octets, each in the range 0 to 255, or 8 bits per number.
Thus, IPv4 provides an addressing capability of 232 or approximately 4.3
billion addresses.
IPv6 Addressing:

2. Chapter 7: Introduction to IPv6

3. Chapter 7: Introduction to IPv6
Advantages of IPv6 over IPv4:
 Larger address space
The main advantage of IPv6 over IPv4 is its larger address space. The length of an IPv6
address is 128 bits, compared with 32 bits in IPv4.The address space therefore has 2128 or
approximately 3.4×1038 addresses.
 Multicasting
Multicasting is the transmission of a packet to multiple destinations in a single send
operation, is part of the base specification in IPv6. In IPv4 this is an optional although
commonly implemented feature.IPv6 multicast addressing shares common features and
protocols with IPv4 multicast, but also provides changes and improvements by eliminating
the need for certain protocols.
 Stateless address auto-configuration (SLAAC)
IPv6 hosts can configure themselves automatically when connected to an IPv6 network using
the Neighbor Discovery Protocol via Internet Control Message Protocol version 6 (ICMPv6)
router discovery messages.
If IPv6 stateless address auto-configuration is unsuitable for an application, a network may
use stateful configuration with the Dynamic Host Configuration Protocol version 6
(DHCPv6) or hosts may be configured manually using static methods.
 Network-layer security
Internet Protocol Security (IPsec) was originally developed for IPv6, but found widespread
deployment first in IPv4, for which it was re-engineered. IPsec was a mandatory specification
of the base IPv6 protocol suite.
 Simplified processing by routers
In IPv6, the packet header and the process of packet forwarding have been simplified.
Although IPv6 packet headers are at least twice the size of IPv4 packet headers, packet
processing by routers is generally more efficient, thereby extending the end-to-end principle
of Internet design.
 Mobility
Unlike mobile IPv4, mobile IPv6 avoids triangular routing and is therefore as efficient as
native IPv6. IPv6 routers may also allow entire subnets to move to a new router connection
point without renumbering.
 Options extensibility
The IPv6 packet header has a fixed size (40 octets). Options are implemented as additional
extension headers after the IPv6 header, which limits their size only by the size of an entire
packet. The extension header mechanism makes the protocol extensible in that it allows
future services for quality of service, security, mobility, and others to be added without
redesign of the basic protocol.
 Jumbograms
IPv4 limits packets to 65535 (216−1) octets of payload. An IPv6 node can optionally handle
packets over this limit, referred to as jumbograms, which can be as large as 4294967295

4. Chapter 7: Introduction to IPv6
(232−1) octets. The use of jumbograms may improve performance over high-MTU
(Maximum Tranmission Unit) links. The use of jumbograms is indicated by the Jumbo
Payload Option header.
 Privacy
Like IPv4, IPv6 supports globally unique IP addresses by which the network activity of each
device can potentially be tracked.
The design of IPv6 intended to re-emphasize the end-to-end principle of network design that
was originally conceived during the establishment of the early Internet. In this approach each
device on the network has a unique address globally reachable directly from any other
location on the Internet.
IPv4 VS IPv6 Header
An IPv4 header contains the following fields:
version The IP version number, 4.
length The length of the datagram header in 32-bit words.
type of service Contains five subfields that specify the precedence, delay, throughput,
reliability, and cost desired for a packet. (The Internet does not guarantee this request.) This
field is not widely used on the Internet.
total length The length of the datagram in bytes including the header, options, and the
appended transport protocol segment or packet.
Identification An integer that identifies the datagram.

5. Chapter 7: Introduction to IPv6
Flags:Controls datagram fragmentation together with the identification field. The flags
indicate whether the datagram may be fragmented, whether the datagram is fragmented, and
whether the current fragment is the final one.
fragment offset The relative position of this fragment measured from the beginning of the
original datagram in units of 8 bytes.
time to live How many routers a datagram can pass through. Each router decrements this
value by 1 until it reaches 0 when the datagram is discarded. This keeps misrouted datagrams
from remaining on the Internet forever.
Protocol The high-level protocol type.
header checksum A number that is computed to ensure the integrity of the header values.
source address The 32-bit IPv4 address of the sending host.
destination address The 32-bit IPv4 address of the receiving host.
Options A list of optional specifications for security restrictions, route recording, and source
routing. Not every datagram specifies an options field.
Padding Null bytes which are added to make the header length an integral multiple of 32
bytes as required by the header length field.

6. Chapter 7: Introduction to IPv6
Specifically, IPv6 omits the following fields in its header.
• header length (the length is constant)
• identification
• flags
• fragment offset (this is moved into fragmentation extension headers)
• header checksum (the upper-layer protocol or security extension header handles data
integrity)
IPv6 options improve over IPv4 by being placed in separate extension headers that are
located between the IPv6 header and the transport-layer header in a packet. Most extension
headers are not examined or processed by any router along a packet's delivery path until it
arrives at its final destination. This mechanism improves router performance for packets
containing options. In IPv4, the presence of any options requires the router to examine all
options.
Another improvement is that IPv6 extension headers, unlike IPv4 options, can be of arbitrary
length and the total amount of options that a packet carries is not limited to 40 bytes. This
feature, and the manner in which it is processed, permit IPv6 options to be used for functions
that were not practical in IPv4, such as the IPv6 Authentication and Security Encapsulation
options.
By using extension headers, instead of a protocol specifier and options fields, newly defined
extensions can be integrated more easily into IPv6.
IPV6 Addressing:
Address Representation:
Represented by breaking 128 bit into Eight 16-bit segments (Each 4 Hex character each)
Each segment is written in Hexadecimal separated by colons.
Hex digit are not case sensitive.
Rule 1:
Drop leading zeros:
2001:0050:0000:0235:0ab4:3456:456b:e560
2001:050:0:235:ab4:3456:456b:e560
Rule2:
Successive fields of zeros can be represented as “::” , But double colon appear only once in
the address.
FF01:0:0:0:0:0:0:1
FF01::1
Note : An address parser identifies the number of missing zeros by separating the two parts
and entering 0 until the 128 bits are complete. If two “::” notations are placed in the
address, there is no way to identify the size of each block of zeros.
Ipv4 vs ipv6

7. Chapter 7: Introduction to IPv6
Translation from Ipv4 to IPv6
Until IPv6 completely supplants IPv4, a number of transition mechanisms are needed to
enable IPv6-only hosts to reach IPv4 services and to allow isolated IPv6 hosts and networks
to reach the IPv6 Internet over the IPv4 infrastructure. People have made various proposals
for this transition period:
Dual IP stack implementation
The dual-stack protocol implementation in an operating system is a fundamental IPv4-to-
IPv6 transition technology. It implements IPv4 and IPv6 protocol stacks either independently
or in a hybrid form. The hybrid form is commonly implemented in modern operating systems
that implement IPv6. Dual-stack hosts are described in RFC 4213.
Modern hybrid dual-stack implementations of IPv4 and IPv6 allow programmers to write
networking code that works transparently on IPv4 or IPv6. The software may use hybrid
sockets designed to accept both IPv4 and IPv6 packets. When used in IPv4 communications,
hybrid stacks use an IPv6 application programming interface and represent IPv4 addresses in
a special address format, the IPv4-mapped IPv6 address.

8. Chapter 7: Introduction to IPv6
IPv4-mapped IPv6 addresses
Hybrid dual-stack IPv6/IPv4 implementations recognize a special class of addresses, the
IPv4-mapped IPv6 addresses. In these addresses, the first 80 bits are zero, the next 16 bits are
one, and the remaining 32 bits are the IPv4 address. You may see these addresses with the
first 96 bits written in the standard IPv6 format, and the remaining 32 bits written in the
customary dot-decimal notation of IPv4. For example,ffff:192.0.2.128 represents the IPv4
address 192.0.2.128. A deprecated format for IPv4-compatible IPv6 addresses was :192.0.2.128.
Because of the significant internal differences between IPv4 and IPv6, some of the lower-
level functionality available to programmers in the IPv6 stack does not work identically with
IPv4-mapped addresses. Some common IPv6 stacks do not implement the IPv4-mapped
address feature, either because the IPv6 and IPv4 stacks are separate implementations (e.g.,
Microsoft Windows 2000, XP, and Server 2003), or because of security concerns
(OpenBSD). On these operating systems, a program must open a separate socket for each IP
protocol it uses. On some systems, e.g., the Linux kernel, NetBSD, and FreeBSD, this feature
is controlled by the socket option IPV6_V6ONLY, as specified in RFC 3493.
Tunneling
In order to reach the IPv6 Internet, an isolated host or network must use the existing IPv4
infrastructure to carry IPv6 packets. This is done using a technique known as tunneling,
which encapsulates IPv6 packets within IPv4, in effect using IPv4 as a link layer for IPv6. IP
protocol 41 indicates IPv4 packets which encapsulate IPv6 datagrams. Some routers or
network address translation devices may block protocol 41. To pass through these devices,
you might use UDP packets to encapsulate IPv6 datagrams. Other encapsulation schemes,
such as AYIYA or Generic Routing Encapsulation, are also popular. Conversely, on IPv6-
only internet links, when access to IPv4 network facilities is needed, tunneling of IPv4 over
IPv6 protocol occurs, using the IPv6 as a link layer for IPv4.
Automatic tunneling
Automatic tunneling refers to a technique where the routing infrastructure automatically
determines the tunnel endpoints. Some automatic tunneling techniques are below. 6to4 is
recommended by RFC 3056. It uses protocol 41 encapsulation. Tunnel endpoints are
determined by using a well-known IPv4 any cast address on the remote side, and embedding
IPv4 address information within IPv6 addresses on the local side. 6to4 is widely deployed
today.
Teredo is an automatic tunneling technique that uses UDP encapsulation and can allegedly
cross multiple NAT boxes. IPv6, including 6to4 and Teredo tunneling, are enabled by default
in Windows Vista and Windows 7. Most Unix systems implement only 6to4, but Teredo can
be provided by third-party software such as Miredo.
ISATAP treats the IPv4 network as a virtual IPv6 local link, with mappings from each IPv4
address to a link-local IPv6 address. Unlike 6to4 and Teredo, which are inter-site tunnelling
mechanisms, ISATAP is an intra-site mechanism, meaning that it is designed to provide IPv6
connectivity between nodes within a single organisation.
Configured and automated tunneling (6in4)
In configured tunneling, the tunnel endpoints are explicitly configured, either by an
administrator manually or the operating system's configuration mechanisms, or by an
automatic service known as a tunnel broker; this is also referred to as automated tunneling.

9. Chapter 7: Introduction to IPv6
Configured tunneling is usually more deterministic and easier to debug than automatic
tunneling, and is therefore recommended for large, well-administered networks. Automated
tunneling provides a compromise between the ease of use of automatic tunneling and the
deterministic behaviour of configured tunneling.
Raw encapsulation of IPv6 packets using IPv4 protocol number 41 is recommended for
configured tunneling; this is sometimes known as 6in4 tunneling. As with automatic
tunneling, encapsulation within UDP may be used in order to cross NAT boxes and firewalls.
Proxying and translation for IPv6-only hosts
After the regional Internet registries have exhausted their pools of available IPv4 addresses, it
is likely that hosts newly added to the Internet might only have IPv6 connectivity. For these
clients to have backward-compatible connectivity to existing IPv4-only resources, suitable
IPv6 transition mechanisms must be deployed. One form of address translation is the use of a
dual-stack application-layer proxy server, for example a web proxy.
NAT-like techniques for application-agnostic translation at the lower layers in routers and
gateways have been proposed. The NAT-PT standard was dropped due to a number of
criticisms, however more recently the continued low adoption of IPv6 has prompted a new
standardization effort under the name NAT64.
Application transition
RFC 4038, Application Aspects of IPv6 Transition, is an informational RFC that covers the
topic of IPv4 to IPv6 application transition mechanisms.