Transcript
IPv6
Internet Protocol version 6 (IPv6) is the most recent
version of the Internet Protocol (IP), the communications
protocol that provides an identification and location system for computers on networks and routes traffic across
the Internet. IPv6 was developed by the Internet Engineering Task Force (IETF) to deal with the longanticipated problem of IPv4 address exhaustion. IPv6 is
intended to replace IPv4.[1]
An IPv6 address
(in hexadecimal)
2001:0DB8 : AC10 :FE01: 0000 : 0000 : 0000 : 0000
2001:0DB8: AC10:FE01::
Zeroes can be omitted
0010000000000001:0000110110111000:1010110000010000:1111111000000001:
Every device on the Internet is assigned an IP address
for identification and location definition. With the rapid
growth of the Internet after commercialization in the
1990s, it became evident that far more addresses than
the IPv4 address space has available were necessary to
connect new devices in the future. By 1998, the Internet
Engineering Task Force (IETF) had formalized the successor protocol. IPv6 uses a 128-bit address, theoretically
allowing 2128 , or approximately 3.4×1038 addresses. The
actual number is slightly smaller, as multiple ranges are
reserved for special use or completely excluded from use.
The total number of possible IPv6 address is more than
7.9×1028 times as many as IPv4, which uses 32-bit addresses and provides approximately 4.3 billion addresses.
The two protocols are not designed to be interoperable,
complicating the transition to IPv6. However, several
IPv6 transition mechanisms have been devised to permit
communication between IPv4 and IPv6 hosts.
0000000000000000:0000000000000000:0000000000000000:0000000000000000
Decomposition of the IPv6 address representation into its binary
form
of the protocol, Internet Protocol Version 4 (IPv4). IPv6
was first formally described in Internet standard document RFC 2460, published in December 1998.[2] 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 in routers by placing the responsibility for packet fragmentation into the end points. The
IPv6 subnet size is standardized by fixing the size of the
host identifier portion of an address to 64 bits to facilitate an automatic mechanism for forming the host identifier from link layer addressing information (MAC address). Network security was a design requirement of the
IPv6 architecture, and included the original specification
of IPsec.
IPv6 provides other technical benefits in addition to a
larger addressing space. In particular, it permits hierarchical address allocation methods that facilitate route
aggregation across the Internet, and thus limit the expansion of routing tables. The use of multicast addressing
is expanded and simplified, and provides additional optimization for the delivery of services. Device mobility, IPv6 does not specify interoperability features with IPv4,
security, and configuration aspects have been considered but essentially creates a parallel, independent network.
Exchanging traffic between the two networks requires
in the design of the protocol.
translator gateways employing one of several transition
IPv6 addresses are represented as eight groups mechanisms, such as NAT64, or a tunneling protocol like
of four hexadecimal digits with the groups 6to4, 6in4, or Teredo.
being
separated
by
colons,
for
example
2001:0db8:0000:0042:0000:8a2e:0370:7334,
but
methods to abbreviate this full notation exist.
2 Motivation and origin
1
2.1 IPv4
Main features
Internet Protocol Version 4 (IPv4) was the first publicly
used version of the Internet Protocol. IPv4 was developed
as a research project by the Defense Advanced Research
Projects Agency (DARPA), a United States Department
of Defense agency, before becoming the foundation for
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
1
2
3 COMPARISON WITH IPV4
An IPv4 address (dotted-decimal notation)
172 . 16
. 254 . 1
10101100 . 00010000 . 11111110 . 00000001
One byte =Eight bits
Thirty-two bits (4 x 8), or 4 bytes
Decomposition of the quad-dotted IPv4 address representation to
its binary value
the Internet and the World Wide Web. It is currently described by IETF publication RFC 791 (September 1981),
which replaced an earlier definition (RFC 760, January
1980). 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. Address
exhaustion was not initially a concern in IPv4 as this version was originally presumed to be a test of DARPA’s
networking concepts.[3] During the first decade of operation of the Internet, it became apparent that methods had
to be developed to conserve address space. In the early
1990s, even after the redesign of the addressing system
using a classless network model, it became clear that this
would not suffice to prevent IPv4 address exhaustion, and
that further changes to the Internet infrastructure were
needed.[4]
The last unassigned top-level address blocks of 16 million IPv4 addresses were allocated in February 2011 by
the Internet Assigned Numbers Authority (IANA) to the
five regional Internet registries (RIRs). However, each
RIR still has available address pools and is expected to
continue with standard address allocation policies until
one /8 Classless Inter-Domain Routing (CIDR) block remains. After that, only blocks of 1024 addresses (/22)
will be provided from the RIRs to a local Internet registry (LIR). As of September 2015, all of Asia-Pacific
Network Information Centre (APNIC), the Réseaux IP
Européens Network Coordination Centre (RIPE_NCC),
Latin America and Caribbean Network Information Centre (LACNIC), and American Registry for Internet Numbers (ARIN) have reached this stage.[5][6][7] This leaves
African Network Information Center (AFRINIC) as the
sole regional internet registry that is still using the normal
protocol for distributing IPv4 addresses.
of 1992 the IETF announced a call for white papers.[8] In
September 1993, the IETF created a temporary, ad-hoc
IP Next Generation (IPng) area to deal specifically with
such issues. The new area was led by Allison Mankin
and Scott Bradner, and had a directorate with 15 engineers from diverse backgrounds for direction-setting and
preliminary document review:[4][9] The working-group
members were J. Allard (Microsoft), Steve Bellovin
(AT&T), Jim Bound (Digital Equipment Corporation),
Ross Callon (Wellfleet), Brian Carpenter (CERN), Dave
Clark (MIT), John Curran (NEARNET), Steve Deering
(Xerox), Dino Farinacci (Cisco), Paul Francis (NTT),
Eric Fleischmann (Boeing), Mark Knopper (Ameritech),
Greg Minshall (Novell), Rob Ullmann (Lotus), and Lixia
Zhang (Xerox).[10]
The Internet Engineering Task Force adopted the IPng
model on 25 July 1994, with the formation of several
IPng working groups.[4] By 1996, a series of RFCs was
released defining Internet Protocol version 6 (IPv6), starting with RFC 1883. (Version 5 was used by the experimental Internet Stream Protocol.)
It is widely expected that the Internet will use IPv4 alongside IPv6 for the foreseeable future. Direct communication between the IPv4 and IPv6 network protocols is not
possible; therefore, intermediary trans-protocol systems
are needed as a communication conduit between IPv4 and
IPv6 whether on a single device or among network nodes.
3 Comparison with IPv4
On the Internet, data is transmitted in the form of network
packets. IPv6 specifies a new packet format, designed to
minimize packet header processing by routers.[2][11] Because the headers of IPv4 packets and IPv6 packets are
significantly different, the two protocols are not interoperable. However, in most respects, IPv6 is an extension
of IPv4. Most transport and application-layer protocols
need little or no change to operate over IPv6; exceptions
are application protocols that embed Internet-layer addresses, such as FTP and NTP, where the new address
format may cause conflicts with existing protocol syntax.
3.1 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.[2] The address space therefore
has 2128 or approximately 3.4×1038 addresses.
In addition, the IPv4 address space is poorly allocated,
with approximately 14%, in 2011, of all available addresses utilized.[12] While these numbers are large, it was
2.2 Working-group proposals
not the intent of the designers of the IPv6 address space
to assure geographical saturation with usable addresses.
By the beginning of 1992, several proposals appeared for Rather, the longer addresses simplify allocation of adan expanded Internet addressing system and by the end dresses, enable efficient route aggregation, and allow im-
3.4
Network-layer security
3
plementation of special addressing features. In IPv4,
complex Classless Inter-Domain Routing (CIDR) methods were developed to make the best use of the small address space. The standard size of a subnet in IPv6 is 264
addresses, the square of the size of the entire IPv4 address space. Thus, actual address space utilization rates
will be small in IPv6, but network management and routing efficiency are improved by the large subnet space and
hierarchical route aggregation.
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. When first
connected to a network, a host sends a link-local router
solicitation multicast request for its configuration parameters; routers respond to such a request with a router advertisement packet that contains Internet Layer configuRenumbering an existing network for a new connectivity ration parameters.[15]
provider with different routing prefixes is a major effort If IPv6 stateless address auto-configuration is unsuitable
with IPv4.[13][14] With IPv6, however, changing the pre- for an application, a network may use stateful configurafix announced by a few routers can in principle renum- tion with the Dynamic Host Configuration Protocol verber an entire network, since the host identifiers (the least- sion 6 (DHCPv6) or hosts may be configured manually
significant 64 bits of an address) can be independently using static methods.
self-configured by a host.[15]
Routers present a special case of requirements for address
configuration, as they often are sources of autoconfigu3.2 Multicasting
ration information, such as router and prefix advertisements. Stateless configuration of routers can be achieved
Multicasting, the transmission of a packet to multiple des- with a special router renumbering protocol.[20]
tinations in a single send operation, is part of the base
specification in IPv6. In IPv4 this is an optional although
commonly implemented feature.[16] IPv6 multicast ad- 3.4 Network-layer security
dressing shares common features and protocols with IPv4
multicast, but also provides changes and improvements Internet Protocol Security (IPsec) was originally develby eliminating the need for certain protocols. IPv6 does oped for IPv6, but found widespread deployment first in
not implement traditional IP broadcast, i.e. the transmis- IPv4, for which it was re-engineered. IPsec was a mandasion of a packet to all hosts on the attached link using tory specification of the base IPv6 protocol suite,[2][21]
a special broadcast address, and therefore does not de- but has since been made optional.[22]
fine broadcast addresses. In IPv6, the same result can be
achieved by sending a packet to the link-local all nodes
multicast group at address ff02::1, which is analogous to 3.5 Simplified processing by routers
IPv4 multicasting to address 224.0.0.1. IPv6 also provides for new multicast implementations, including em- In IPv6, the packet header and the process of packet
bedding rendezvous point addresses in an IPv6 multicast forwarding have been simplified. Although IPv6 packet
group address, which simplifies the deployment of inter- headers are at least twice the size of IPv4 packet headdomain solutions.[17]
ers, packet processing by routers is generally more
[2][11]
because less processing is required in
In IPv4 it is very difficult for an organization to get even efficient,
routers.
This
furthers
the end-to-end principle of Interone globally routable multicast group assignment, and the
net
design,
which
envisioned
that most processing in the
[18]
implementation of inter-domain solutions is arcane.
network
occurs
in
the
leaf
nodes.
Unicast address assignments by a local Internet registry
for IPv6 have at least a 64-bit routing prefix, yielding
the smallest subnet size available in IPv6 (also 64 bits).
With such an assignment it is possible to embed the unicast address prefix into the IPv6 multicast address format,
while still providing a 32-bit block, the least significant
bits of the address, or approximately 4.2 billion multicast
group identifiers. Thus each user of an IPv6 subnet automatically has available a set of globally routable sourcespecific multicast groups for multicast applications.[19]
The packet header in IPv6 is simpler than the IPv4
header. Many rarely used fields have been moved to optional header extensions.
IPv6 routers do not perform IP fragmentation. IPv6
hosts are required to either perform path MTU discovery, perform end-to-end fragmentation, or to send packets no larger than the default Maximum transmission unit
(MTU), which is 1280 octets.
The IPv6 header is not protected by a checksum. Integrity protection is assumed to be assured by both the
3.3 Stateless address autoconfiguration link layer or error detection and correction methods in
higher-layer protocols, such as TCP and UDP. In IPv4,
(SLAAC)
UDP may actually have a checksum of 0, indicating no
See also: IPv6 address § Stateless address autoconfigu- checksum; IPv6 requires a checksum in UDP. Therefore,
ration
IPv6 routers do not need to recompute a checksum when
4
4 PACKET FORMAT
header fields change, such as the time to live (TTL) or address unique, exposing the type of hardware used and
hop count.
providing a unique handle for a user’s online activity.
The TTL field of IPv4 has been renamed to Hop Limit It is not a requirement for IPv6 hosts to use address autoin IPv6, reflecting the fact that routers are no longer ex- configuration, however. Yet, even when an address is
pected to compute the time a packet has spent in a queue. not based on the MAC address, the interface’s address
is globally unique, in contrast to NAT-masqueraded private networks. Privacy extensions for IPv6 have been
defined to address these privacy concerns,[28] although
3.6 Mobility
Silvia Hagen describes these as being largely due to
Unlike mobile IPv4, mobile IPv6 avoids triangular rout- “misunderstanding”.[29] When privacy extensions are ening and is therefore as efficient as native IPv6. IPv6 abled, the operating system generates random host identirouters may also allow entire subnets to move to a new fiers to combine with the assigned network prefix. These
ephemeral addresses are used to communicate with rerouter connection point without renumbering.[23]
mote hosts making it more difficult to track a single
device.[30]
3.7
Options extensibility
Privacy extensions are enabled by default in Windows
(since XP SP1), OS X (since 10.7), and iOS (since verThe IPv6 packet header has a minimum size of 40 octets. sion 4.3).[31][32] Some Linux distributions have enabled
Options are implemented as extensions. This provides privacy extensions as well.[33]
the opportunity to extend the protocol in the future withmentioned
out affecting the core packet structure.[2] However, recent In addition to the “temporary” addresses
[34]
Interface
studies indicate that there is still widespread dropping of above, there are also “stable” addresses:
Identifiers are generated such that they are stable for each
IPv6 packets that contain extension headers.[24]
subnet, but change as a host moves from one network to
another. In this way it is difficult to track a host as it
moves from network to network, but with-in a particular
3.8 Jumbograms
network it will always have the same address (unless the
IPv4 limits packets to 65,535 (216 −1) octets of payload. state used in generating the address is reset and the alAn IPv6 node can optionally handle packets over this gorithm is run again) so that network access controls and
limit, referred to as jumbograms, which can be as large auditing can be potentially be configured.
as 4,294,967,295 (232 −1) octets. The use of jumbograms Privacy extensions do not protect the user from other
may improve performance over high-MTU links. The use forms of activity tracking, such as tracking cookies or
of jumbograms is indicated by the Jumbo Payload Option browser fingerprinting.
header.[25]
3.9
Privacy
4 Packet format
Like IPv4, IPv6 supports globally unique IP addresses by
which the network activity of each device can potentially Main article: IPv6 packet
be tracked. The design of IPv6 intended to re-emphasize An IPv6 packet has two parts: a header and payload.
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.
Network prefix tracking is less of a concern if the user’s
ISP assigns a dynamic network prefix via DHCP.[26][27]
Privacy extensions do little to protect the user from tracking if the ISP assigns a static network prefix. In this scenario, the network prefix is the unique identifier for tracking and the interface identifier is secondary.
In IPv4 the effort to conserve address space with network
address translation (NAT) obfuscates network address
spaces, hosts, and topologies. In IPv6 when using address auto-configuration, the Interface Identifier (MAC
address) of an interface port is used to make its public IP IPv6 packet header
5.1
Stateless address autoconfiguration (SLAAC)
5
The header consists of a fixed portion with minimal func- host is connected, and the least-significant 64 bits are the
tionality required for all packets and may be followed by identifier of the host interface on the subnet. This means
optional extensions to implement special features.
that the identifier need only be unique on the subnet to
which simplifies the detecThe fixed header occupies the first 40 octets (320 bits) of which the host is connected,
[38]
tion
of
duplicate
addresses.
the IPv6 packet. It contains the source and destination addresses, traffic classification options, a hop counter, and
the type of the optional extension or payload which follows the header. This Next Header field tells the receiver
how to interpret the data which follows the header. If the
packet contains options, this field contains the option type
of the next option. The “Next Header” field of the last option, points to the upper-layer protocol that is carried in
the packet’s payload.
5.1.1 Link local address
All IPv6 hosts require a link-local address. This is derived
from the MAC address of each interface and the linklocal prefix FE80::/10. The process involves filling the
Extension headers carry options that are used for special address space with prefix bits left-justified to the mosttreatment of a packet in the network, e.g., for routing, significant bit, and filling the MAC address in EUI-64
fragmentation, and for security using the IPsec frame- format into the least-significant bits. If any bits remain to
be filled between the two parts, those are set to zero.[38]
work.
Without special options, a payload must be less than The uniqueness of the address on the subnet is tested with
[39]
64KB. With a Jumbo Payload option (in a Hop-By-Hop the Duplicate Address Detection (DAD) method.
Options extension header), the payload must be less than
4 GB.
5.1.2 Address uniqueness
Unlike with IPv4, routers never fragment a packet. Hosts
are expected to use Path MTU Discovery to make their Hosts verify the uniqueness of addresses assigned by
packets small enough to reach the destination without sending a neighbor solicitation message asking for the
needing to be fragmented. See IPv6 packet fragmenta- Link Layer address of the IP address. If any other host
is using that address, it responds. However, MAC adtion.
dresses are designed to be unique on each network card
which minimizes chances of duplication.[40]
5
Addressing
Main article: IPv6 address
Compared to IPv4, the most obvious advantage of IPv6
is its larger address space. IPv4 addresses are 32 bits
long which provides approximately 4.3×109 (4.3 billion)
addresses.[35] IPv6 addresses are 128 bits long, resulting
in an address space of 3.4×1038 (340 undecillion) addresses. Such a large space is deemed sufficient for the
foreseeable future.[36]
IPv6 addresses are written in eight groups
The groups
of four hexadecimal digits.
are
separated
by
colons,
for
example,
2001:0db8:85a3:0000:0000:8a2e:0370:7334.
IPv6
unicast addresses other than those that start with binary 000 are logically divided into two parts: a 64-bit
(sub-)network prefix, and a 64-bit interface identifier.[37]
5.1
Stateless address autoconfiguration
(SLAAC)
An IPv6 host may generate its own IP address and test
the uniqueness of a generated address in the addressing
scope intended. IPv6 addresses consist of two parts. The
most-significant 64 bits are the subnet prefix to which the
The host first determines if the network is connected to
any routers at all, because if not, then all nodes are reachable using the link-local address that already is assigned
to the host. The host will send out a Router Solicitation
message to the all-routers[41][42] multicast group with its
link local address as source. If there is no answer after
a predetermined number of attempts, the host concludes
that no routers are connected. If it does get a response
from a router, there will be network information inside
that is needed to create a globally unique address. There
are also two flag bits that tell the host whether it should
use DHCP to get further information and addresses:
• The Manage bit, that indicates whether or not the
host should use DHCP to obtain additional addresses
• The Other bit, that indicates whether or not the host
should obtain other information through DHCP. The
other information consists of one or more prefix information options for the subnets that the host is attached to, a lifetime for the prefix, and two flags:[40]
• On-link: If this flag is set, the host will treat all
addresses on the specific subnet as being onlink, and send packets directly to them instead
of sending them to a router for the duration of
the given lifetime.
• Address: This is the flag that tells the host to
actually create a global address.
6
5.1.3
6 TRANSITION MECHANISMS
Global addressing
(:). The address 2001:0db8:0000:0000:0000:ff00:0042:
8329 is an example of this representation.
The assignment procedure for global addresses is sim- For convenience, an IPv6 address may be abbreviated to
ilar to local address construction. The prefix is sup- shorter notations by application of the following rules,
plied from router advertisements on the network. Mul- where possible.
tiple prefix announcements cause multiple addresses to
be configured.[40]
• One or more leading zeroes from any groups of hexadecimal digits are removed; this is usually done to
Stateless address autoconfiguration (SLAAC) requires a
either all or none of the leading zeroes. For exam/64 address block, as defined in RFC 4291. Local Interple, the group 0042 is converted to 42.
net registries are assigned at least /32 blocks, which they
divide among subordinate networks.[43] The initial rec• Consecutive sections of zeroes are replaced with a
ommendation stated assignment of a /48 subnet to enddouble colon (::). The double colon may only be
consumer sites (RFC 3177). This was replaced by RFC
used once in an address, as multiple use would ren6177, which “recommends giving home sites significantly
der the address indeterminate. RFC 5952 recommore than a single /64, but does not recommend that evmends that a double colon must not be used to deery home site be given a /48 either”. /56s are specifinote an omitted single section of zeroes.[45]
cally considered. It remains to be seen if ISPs will honor
this recommendation. For example, during initial trials,
An example of application of these rules:
Comcast customers were given a single /64 network.[44]
IPv6 addresses are classified by three types of networking
Initial
address:
methodologies: unicast addresses identify each network
2001:0db8:0000:0000:0000:ff00:0042:8329
interface, anycast addresses identify a group of interfaces,
After removing all leading zeroes in each
usually at different locations of which the nearest one is
group: 2001:db8:0:0:0:ff00:42:8329
automatically selected, and multicast addresses are used
After omitting consecutive sections of zeroes:
to deliver one packet to many interfaces. The broadcast
2001:db8::ff00:42:8329
method is not implemented in IPv6. Each IPv6 address
has a scope, which specifies in which part of the network
loopback
address,
it is valid and unique. Some addresses are unique only on The
0000:0000:0000:0000:0000:0000:0000:0001,
may
the local (sub-)network. Others are globally unique.
be abbreviated to ::1 by using both rules.
Some IPv6 addresses are reserved for special purposes,
such as loopback, 6to4 tunneling, and Teredo tunneling, As an IPv6 address may have more than one representaa proposed standard for repreas outlined in RFC 5156. Also, some address ranges are tion, the IETF has issued
[46]
senting
them
in
text.
considered special, such as link-local addresses for use
on the local link only, Unique Local addresses (ULA),
as described in RFC 4193, and solicited-node multicast
6 Transition mechanisms
addresses used in the Neighbor Discovery Protocol.
IPv6 is not foreseen to supplant IPv4 instantaneously.
Both protocols will continue to operate simultaneously
for some time. Therefore, some IPv6 transition mechaMain article: IPv6 address § IPv6 addresses in the nisms are needed to enable IPv6 hosts to reach IPv4 serDomain Name System
vices and to allow isolated IPv6 hosts and networks to
reach each other over IPv4 infrastructure.[47]
In the Domain Name System, hostnames are mapped Many of these transition mechanisms use tunneling to ento IPv6 addresses by AAAA resource records, so-called capsulate IPv6 traffic within IPv4 networks. This is an
quad-A records. For reverse resolution, the IETF re- imperfect solution, which reduces the maximum transserved the domain ip6.arpa, where the name space is hi- mission unit (MTU) of a link and therefore complierarchically divided by the 1-digit hexadecimal represen- cates Path MTU Discovery, and may increase latency.[48]
tation of nibble units (4 bits) of the IPv6 address. This Tunneling protocols are a temporary solution for netscheme is defined in RFC 3596.
works that do not support native dual-stack, where both
IPv6 and IPv4 run independently.
5.2
IPv6 in the Domain Name System
5.3
Address representation
6.1 Dual IP stack implementation
The 128 bits of an IPv6 address are represented in 8
groups of 16 bits each. Each group is written as 4 hex- Dual-stack (or native dual-stack) IP implementations proadecimal digits and the groups are separated by colons vide complete IPv4 and IPv6 protocol stacks in the same
6.3
Proxying and translation for IPv6-only hosts
7
network node. This facilitates native communications be- be provided by third-party software such as Miredo.
tween nodes using either protocol. The method is defined ISATAP (Intra-Site Automatic Tunnel Addressing
in RFC 4213.[49]
Protocol)[55] uses the IPv4 network as a virtual IPv6
This is the most desirable IPv6 implementation during the local link, with mappings from each IPv4 address to
transition from IPv4 to IPv6, as it avoids the complexities a link-local IPv6 address. Unlike 6to4 and Teredo,
of tunneling, such as security, increased latency, manage- which are inter-site tunneling mechanisms, ISATAP is
ment overhead, and a reduced PMTU.[50] However, it is an intra-site mechanism, meaning that it is designed to
not always possible, since outdated network equipment provide IPv6 connectivity between nodes within a single
may not support IPv6.
organization.
Dual-stack software design is a transitional technique to
facilitate the adoption and deployment of IPv6. However,
it might introduce more security threats as hosts could
be subject to attacks from both IPv4 and IPv6. It has
been argued that dual-stack could ultimately overburden
the global networking infrastructure by requiring routers
to deal with IPv4 and IPv6 routing simultaneously.[51]
6.2.2 Configured and automated tunneling (6in4)
6in4 tunneling requires the tunnel endpoints to be explicitly configured, either by an administrator manually or
the operating system’s configuration mechanisms, or by
an automatic service known as a tunnel broker;[56] this is
also referred to as automated tunneling. Configured tunneling is usually more deterministic and easier to debug
6.2 Tunneling
than automatic tunneling, and is therefore recommended
for large, well-administered networks. Automated tunMany current Internet users do not have IPv6 dual-stack neling provides a compromise between the ease of use
support, and thus cannot reach IPv6 sites directly. In- of automatic tunneling and the deterministic behavior of
stead, they must use IPv4 infrastructure to carry IPv6 configured tunneling.
packets. This is done using a technique known as
tunneling, which encapsulates IPv6 packets within IPv4, Raw encapsulation of IPv6 packets using IPv4 protocol
number 41 is recommended for configured tunneling; this
in effect using IPv4 as a link layer for IPv6.
is sometimes known as 6in4 tunneling. As with automatic
IP protocol 41 indicates IPv4 packets which encapsulate tunneling, encapsulation within UDP may be used in orIPv6 datagrams. Some routers or network address trans- der to cross NAT boxes and firewalls.
lation devices may block protocol 41. To pass through
these devices, UDP packets may be used to encapsulate
IPv6 datagrams. Other encapsulation schemes, such as 6.3 Proxying and translation for IPv6-only
AYIYA or Generic Routing Encapsulation, are also pophosts
ular.
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.
6.2.1
Automatic tunneling
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
Automatic tunneling refers to a technique by which the application-layer proxy server, for example a web proxy.
routing infrastructure automatically determines the tun- NAT-like techniques for application-agnostic translation
nel endpoints. Some automatic tunneling techniques are at the lower layers in routers and gateways have been probelow.
posed. The NAT-PT standard was dropped because of
[57]
6to4 is recommended by RFC 3056. It uses protocol 41 criticisms; however, more recently, the continued low
encapsulation.[52] Tunnel endpoints are determined by us- adoption of IPv6 has prompted a new standardization efing a well-known IPv4 anycast address on the remote side, fort of a technology called NAT64.
and embedding IPv4 address information within IPv6 addresses on the local side. 6to4 is the most common tunnel
protocol currently deployed.
7 IPv6 readiness
Teredo is an automatic tunneling technique that uses
UDP encapsulation and can allegedly cross multiple NAT
nodes.[53] IPv6, including 6to4 and Teredo tunneling, are
enabled by default in Windows Vista[54] and Windows 7.
Most Unix systems implement only 6to4, but Teredo can
Compatibility with IPv6 networking is mainly a software
or firmware issue. However, much of the older hardware
that could in principle be upgraded is likely to be replaced
instead. The American Registry for Internet Numbers
8
8 DEPLOYMENT
(ARIN) suggested that all Internet servers be prepared to The CableLabs consortium published the 160 Mbit/s
serve IPv6-only clients by January 2012.[58]
DOCSIS 3.0 IPv6-ready specification for cable modems
in August 2006. The widely used DOCSIS 2.0 does not
support IPv6. The new 'DOCSIS 2.0 + IPv6' standard
supports IPv6, which may on the cable modem side re7.1 Software
quire only a firmware upgrade.[62][63] It is expected that
Host software may have only IPv4 or only IPv6 network- only 60% of cable modems’ servers and 40% of cable
[64]
ing software, or it may support dual-stack, or hybrid dual- modems will be DOCSIS 3.0 by 2011. However, most
stack operation. The majority of personal computers ISPs that support DOCSIS 3.0 do not support IPv6 across
running recent operating system versions support IPv6. their networks.
Many popular applications with networking capabilities Other equipment which is typically not IPv6-ready ranges
are compliant.
from VoIP devices to laboratory equipment and printers.
Some software transitioning mechanisms are outlined in
RFC 4038, RFC 3493, and RFC 3542.
7.3 Shadow networks
7.1.1
IPv4-mapped IPv6 addresses
Hybrid dual-stack IPv6/IPv4 implementations recognize
a special class of addresses, the IPv4-mapped IPv6 addresses. These addresses consist of an 80-bit prefix of
zeros, the next 16 bits are one, and the remaining, leastsignificant 32 bits contain the IPv4 address. These addresses are typically written with a 96-bit prefix 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 is ::192.0.2.128.[59]
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
the same when used 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).[60] 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.[61]
7.2
Hardware and embedded systems
One side effect of IPv6 implementation may be the emergence of so-called shadow networks caused by IPv6 traffic flowing into IPv4 networks when IPv6 enabled nodes
are added to the existing network, and the IPv4 security
in place is unable to properly identify it. This may occur with operating system upgrades, when the newer OS
enables IPv6 support by default, while the older one did
not. Failing to update the security infrastructure to accommodate IPv6 can lead to IPv6 traffic bypassing it.[65]
Shadow networks have been found occurring on business
networks in which enterprises are replacing Windows XP
systems that do not have an IPv6 stack enabled by default,
with Windows 7 systems, that do.[66] Some IPv6 stack implementors have therefore recommended to disable IPv4
mapped addresses and to instead use a dual-stack network
where supporting both IPv4 and IPv6 is necessary.[67]
8 Deployment
Main article: IPv6 deployment
The 1993 introduction of Classless Inter-Domain Routing (CIDR) in the routing and IP address allocation for
the Internet, and the extensive use of network address
translation (NAT) delayed IPv4 address exhaustion. The
final phase of exhaustion started on 3 February 2011.[68]
However, despite a decade long development and implementation history as a Standards Track protocol, general worldwide deployment of IPv6 is increasing slowly.
As of September 2013, about 4% of domain names and
16.2% of the networks on the Internet have IPv6 protocol
support.[69]
Basic infrastructure equipment, such as network adapters
and network switches, may not be affected by the change,
since they transmit link layer frames without inspecting
the contents. Most equipment may be IPv6 capable with
a software or firmware update if the device has sufficient IPv6 has been implemented on all major operating sysstorage and memory space for the new IPv6 stack.
tems in use in commercial, business, and home consumer
In some cases, non-compliant equipment needs to be re- environments. Since 2008, the domain name system can
placed because the manufacturer no longer exists or soft- be used in IPv6. IPv6 was first used in a major world
ware updates are not possible, for example, because the event during the 2008 Summer Olympic Games,[70] the
network stack is implemented in permanent read-only largest showcase of IPv6 technology since the incepmemory.
tion of IPv6.[71] Some governments including the Federal
9
government of the United States and China have issued
guidelines and requirements for IPv6 capability.
[8] Bradner, S.; Mankin, A. (December 1993). “IP: Next
Generation (IPng) White Paper Solicitation”. RFC 1550.
In 2009, Verizon mandated IPv6 operation and depre- [9] “History of the IPng Effort”. Sun.
cated IPv4 as an optional capability for cellular (LTE)
hardware.[72] As of June 2012, T-Mobile USA also sup- [10] “The Recommendation for the IP Next Generation Protocol – Appendix B”. RFC 1752.
ports external IPv6 access.[73]
As of 2014, IPv4 still carried more than 99% of worldwide Internet traffic.[74][75] The internet exchange in Amsterdam is the only big exchange which publicly shows the
IPv6 traffic percentage, which as of November 2015 is
tracking at about 1.2%, growing at about 0.3 percentage
points per year.[76] As of 31 December 2015, the percentage of users reaching Google services with IPv6 reached
10.0% for the first time, growing at about 4.3 percentage
points per year, although varying widely by region.[77] As
of 18 April 2015 Deployment of IPv6 on web servers also
varied widely, with over half of web pages available via
IPv6 in many regions, with about 16% of web servers
supporting IPv6.[78]
9
See also
• China Next Generation Internet
• Comparison of IPv6 support in operating systems
[11] Partridge, C.; Kastenholz, F. (December 1994).
“Technical Criteria for Choosing IP The Next Generation
(IPng)". RFC 1726.
[12] “Moving to IPv6: Now for the hard part (FAQ)". Deep
Tech. CNET News. Retrieved 3 February 2011.
[13] Ferguson, P.; Berkowitz, H. (January 1997). “Network
Renumbering Overview: Why would I want it and what is
it anyway?". RFC 2071.
[14] Berkowitz, H. (January 1997). “Router Renumbering
Guide”. RFC 2072.
[15] Thomson, S.; Narten, T.; Jinmei, T. (September 2007).
“IPv6 Stateless Address Autoconfiguration”. RFC 4862.
[16] RFC 1112, Host extensions for IP multicasting, S. Deering
(August 1989)
[17] RFC 3956, Embedding the Rendezvous Point (RP) Address
in an IPv6 Multicast Address, P. Savola, B. Haberman
(November 2004)
• Comparison of IPv6 support in common applications
[18] RFC 2908, The Internet Multicast Address Allocation Architecture, D. Thaler, M. Handley, D. Estrin (September
2000)
• DoD IPv6 product certification
[19] RFC 3306, Unicast-Prefix-based IPv6 Multicast Addresses, B. Haberman, D. Thaler (August 2002)
• List of IPv6 tunnel brokers
• University of New Hampshire InterOperability Laboratory
10
References
[1] New Zealand IPv6 Task Force. “FAQs”. Retrieved 26
October 2015.
[2] RFC 2460, Internet Protocol, Version 6 (IPv6) Specification, S. Deering, R. Hinden (December 1998)
[3] Google IPv6 Conference 2008: What will the IPv6 Internet
look like?. Event occurs at 13:35.
[4] Bradner, S.; Mankin, A. (January 1995). “The Recommendation for the IP Next Generation Protocol”. RFC
1752.
[5] Rashid, Fahmida. “IPv4 Address Exhaustion Not Instant
Cause for Concern with IPv6 in Wings”. eWeek. Retrieved 23 June 2012.
[6] Ward, Mark. “Europe hits old internet address limits”.
BBC. Retrieved 15 September 2012.
[7] Huston, Geoff. “IPV4 Address Report”.
[20] RFC 2894, Router Renumbering for IPv6, M. Crawford,
August 2000.
[21] RFC 4301, IPv6 Node Requirements”, J. Loughney (April
2006)
[22] RFC 6434, IPv6 Node Requirements, E. Jankiewicz, J.
Loughney, T. Narten (December 2011)
[23] RFC 3963, Network Mobility (NEMO) Basic Protocol Support, V. Devarapalli, R. Wakikawa, A. Petrescu, P. Thubert (January 2005)
[24] Gont, F.; Linkova, J.; Chown, T.; Liu, S. (October 2015).
“Observations on the Dropping of Packets with IPv6 Extension Headers in the Real World”. draft-ietf-v6ops-ipv6ehs-in-real-world-01.
[25] RFC 2675, IPv6 Jumbograms, D. Borman, S. Deering, R.
Hinden (August 1999)
[26] Statement on IPv6 Address Privacy, Steve Deering &
Bob Hinden, Co-Chairs of the IETF’s IP Next Generation
Working Group, 6 November 1999.
[27] “Neues Internet-Protokoll erschwert anonymes Surfen”.
Spiegel.de. Retrieved 19 February 2012.
[28] Marten, T; Draves, R (January 2001). Privacy Extensions
for Stateless Address Autoconfiguration in IPv6.
10
[29] IPv6 Essentials by Silvia Hagen, p. 28, chapter 3.5.
10
REFERENCES
[30] Privacy Extensions (IPv6), Elektronik Kompendium.
[50] “IPv6: Dual stack where you can; tunnel where you must”.
www.networkworld.com. 5 September 2007. Retrieved
27 November 2012.
[31] Overview of the Advanced Networking Pack for Windows
XP, Revision: 8.14
[51] Sun, Charles C. (1 May 2014). “Stop using Internet Protocol Version 4!". Computerworld.
[32] IPv6: Privacy Extensions einschalten, Reiko Kaps, 13
April 2011
[52] RFC 3056, Connection of IPv6 Domains via IPv4 Clouds,
B. Carpenter, February 2001.
[33] “Comment #61 : Bug #176125 : Bugs: “procps” package: Ubuntu”. Bugs.launchpad.net. Retrieved 19 February 2012.
[53] RFC 4380, Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs), C. Huitema, Februari 2006
[34] Gont, F (April 2014). A Method for Generating Semantically Opaque Interface Identifiers with IPv6 Stateless
Address Autoconfiguration (SLAAC). RFC 7217. https:
//tools.ietf.org/html/rfc7217.
[54] “The Windows Vista Developer Story: Application Compatibility Cookbook”. Msdn2.microsoft.com. 24 April
2006. Retrieved 20 January 2012.
[35] RFC 4291, IP Version 6 Addressing Architecture, R. Hinden, S. Deering (February 2006)
[55] RFC 5214, Intra-Site Automatic Tunnel Addressing Protocol (ISATAP), F. Templin, T. Gleeson, D. Thaler, March
2008.
[36] “The sheer size of IPv6”. Pthree.org. 8 March 2009. Retrieved 20 January 2012.
[37] RFC 4291, p. 9
[38] RFC 3315, R. Droms, J. Bound, B. Volz, T. Lemon, C.
Perkins, and M. Carney, Dynamic Host Configuration Protocol for IPv6 (DHCPv6), July 2003 (Proposed Standard)
[39] S. Thomson, T. Narten, and T. Jinmei, ‘IPv6 Stateless Address Autoconfiguration’, Internet Request for Comments,
vol. RFC 4862 (Draft Standard), Sep. 2007 [Online].
Available: http://www.rfc-editor.org/rfc/rfc4862.txt
[40] T. Narten, ‘Neighbor discovery and stateless autoconfiguration in IPv6’, IEEE Internet Computing, vol. 3, no. 4,
pp. 54–62, Aug. 1999. DOI: 10.1109/4236.780961
[41] RFC 4862, IPv6 Stateless Address Autoconfiguration,
S.Thomson (September 2007), section 5.5.1: http://tools.
ietf.org/html/rfc4862#section-5.5.1
[56] RFC 3053, IPv6 Tunnel Broker, A. Durand, P. Fasano, I.
Guardini, D. Lento (January 2001)
[57] RFC 4966, Reasons to Move the Network Address
Translator-Protocol Translator (NAT-PT) to Historic Status
[58] “Web sites must support IPv6 by 2012, expert warns”.
Network World. 21 January 2010. Retrieved 30 September 2010.
[59] "RFC 4291". RFC 4291. IETF.
[60] “OpenBSD inet6(4) manual page”. Openbsd.org. 13 December 2009. Retrieved 20 January 2012.
[61] “Basic Socket Interface Extensions for IPv6”. RFC 3493.
IETF. Retrieved 2012-01-20.
[62] “DOCSIS 2.0 Interface”. Cablemodem.com. 29 October
2007. Retrieved 31 August 2009.
[42] RFC 4861, Neighbor Discovery for IP version 6 (IPv6),
T.Narten (September 2007), section 6.3.7: http://tools.
ietf.org/html/rfc4861#section-6.3.7
[63] “RMV6TF.org” (PDF). Archived from the original (PDF)
on 5 January 2012. Retrieved 20 January 2012.
[43] “IPv6 Address Allocation and Assignment Policy”. RIPE
NCC. 8 February 2011. Retrieved 27 March 2011.
[64] “DOCSIS 3.0 Network Equipment Penetration to Reach
60% by 2011” (Press release). ABI Research. 23 August
2007. Retrieved 30 September 2007.
[44] “Comcast Activates First Users With IPv6 Native Dual
Stack Over DOCSIS”. Comcast. 31 January 2011.
[45] RFC 5952, A Recommendation for IPv6 Address Text Representation, S. Kawamura (August 2010), section 4.2.2:
http://tools.ietf.org/html/rfc5952#section-4.2.2
[46] RFC 5952, A Recommendation for IPv6 Address Text Representation, S. Kawamura (August 2010)
[47] “IPv6 Transition Mechanism / Tunneling Comparison”.
Sixxs.net. Retrieved 20 January 2012.
[48] “Advisory Guidelines for 6to4 Deployment”. RFC 6343.
IETF.
[49] “Basic Transition Mechanisms for IPv6 Hosts and
Routers”. RFC 4213. IETF.
[65] Mullins, Robert (April 5, 2012), Shadow Networks: an
Unintended IPv6 Side Effect, retrieved March 2, 2013
[66] Cicileo, Guillermo; Gagliano, Roque; O’Flaherty, Christian; et al. (October 2009). IPv6 For All: A Guide for IPv6
Usage and Application in Different Environments (PDF).
p. 5. Retrieved March 2, 2013.
[67] Jun-ichiro itojun Hagino (October 2003). “IPv4-Mapped
Addresses on the Wire Considered Harmful”.
[68] “IPv4 Address Report”. Potaroo.net. Retrieved 20 January 2012.
[69] Mike Leber (2 October 2010). “Global IPv6 Deployment
Progress Report”. Hurricane Electric. Retrieved 19 October 2011.
11
[70] “Beijing2008.cn leaps to next-generation Net” (Press release). The Beijing Organizing Committee for the Games
of the XXIX Olympiad. 30 May 2008.
[71] Das, Kaushik (2008). “IPv6 and the 2008 Beijing
Olympics”. IPv6.com. Retrieved 15 August 2008. As
thousands of engineers, technologists have worked for a
significant time to perfect this (IPv6) technology, there
is no doubt, this technology brings considerable promises
but this is for the first time that it will showcase its strength
when in use for such a mega-event.
[72] Derek Morr (9 June 2009). “Verizon Mandates IPv6 Support for Next-Gen Cell Phones”. CircleID.
[73] theipv6guy (31 July 2012). “T-Mobile USA Launches External IPv6”. T-Mobile.
[74] van Beijnum, Iljitsch. “IPv6 adoption starting to add up
to real numbers: 0.6 percent”. Ars Technica. Retrieved 9
April 2015.
[75] David Frost (20 April 2011). “Ipv6 traffic volumes going
backwards”. iTWire. Retrieved 19 February 2012.
[76] “Amsterdam Internet Exchange Ether Type”. ams-ix.net.
Retrieved 2015-10-06.
[77] “IPv6”. Google Statistics. Google. Retrieved 27 April
2015.
[78] “6lab IPv6 website”. 6lab.cisco.com. Retrieved 2015-0128.
11
External links
• IPv6 in the Linux Kernel by Rami Rosen.
• Free Pool of IPv4 Address Space Depleted
• An Introduction and Statistics about IPV6
12
12
12
12.1
TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES
Text and image sources, contributors, and licenses
Text
• IPv6 Source: https://en.wikipedia.org/wiki/IPv6?oldid=700613501 Contributors: The Anome, Arcade~enwiki, Youssefsan, Aldie, PierreAbbat, Nate Silva, Hfastedge, Edward, Zhackwyatt, Bdesham, Nealmcb, JohnOwens, Nixdorf, Pnm, Lousyd, Phoe6, Karada, Mcarling,
Iluvcapra, CesarB, Ahoerstemeier, Cyp, Anders Feder, Haakon, Ronz, Julesd, Trisweb, Cyan, Stefan-S, Scott, Tristanb, Cherkash, HPA,
Ehn, Adam Conover, Hashar, Mulad, Feedmecereal, Ilja Lorek, Ww, Random832, The Anomebot, Marcod'Itri, Tpbradbury, Furrykef,
Jnc, EthanL, Omegatron, HarryHenryGebel, AnonMoos, Wetman, Jamesday, Mordomo, Northgrove, Chuunen Baka, RickBeton, Robbot,
Paranoid, RichiH, Dale Arnett, Hankwang, Noldoaran, Astronautics~enwiki, Pigsonthewing, Fredrik, Chris 73, Vespristiano, RedWolf,
Donreed, Digizen, Peak, Nurg, Ashley Y, Rfc1394, PedroPVZ, Paradox2, Jondel, TheLight, Victor, GerardM, Trevor Johns, David Edgar,
Seano1, Pengo, Terjepetersen, David Gerard, SmilingBoy, Dave6, Antonis Christofides, Alexwcovington, Centrx, Giftlite, Yama, Msiebuhr,
Jtg, Omegium, Mintleaf~enwiki, Holizz, Dzenizo, Karn, Wwoods, Markus Kuhn, Capek, Imarsman, Patrickdavidson, Jason Quinn, Pascal666, Rchandra, AlistairMcMillan, Macrakis, Foobar, Albany45, SWAdair, Bobblewik, Wmahan, Bgraabek, LucasVB, HorsePunchKid,
Beland, Dnas, ThG, Robert Brockway, Kaldari, ShakataGaNai, Yayay, Nzseries1, DragonflySixtyseven, Naff89, Semenko, Bumm13, Sam
Hocevar, Beoba, Bbpen, AnandKumria, GreenReaper, ChrisErbach, Konikofi, Mike Rosoft, N328KF, Imroy, Sysy, JTN, EugeneZelenko,
Erc, Discospinster, Rich Farmbrough, Alexkon, FT2, Vsmith, Wk muriithi, ArnoldReinhold, Paolopal~enwiki, Dolda2000, Bender235,
El C, Cap'n Refsmmat, Richard W.M. Jones, PhilHibbs, Spearhead, Southen, RoyBoy, Bobo192, Mike Schwartz, Eldar, BrokenSegue,
Cmdrjameson, Cwolfsheep, Tmh, Guiltyspark, Giraffedata, Chbarts, Nhandler, Minghong, Towel401, Wrs1864, Helix84, Krellis, Nsaa,
Kvaks, Jhd, Drangon, Jumbuck, Zachlipton, Alansohn, PaulHanson, Adamthewebman, Rd232, Droob, Hypersonic, Water Bottle, RoySmith, Psz, Laug, Oneliner, Vedantm, Rick Sidwell, Paul1337, ReyBrujo, Mark Bergsma, Stephan Leeds, Suruena, Evil Monkey, Snorgy,
Kusma, Voxadam, Yurivict, JameySharp, Dan100, Rdenis, Euphrosyne, 4c27f8e656bb34703d936fc59ede9a, Kbolino, Kenyon, Kynan,
WayneMokane, Gmaxwell, Weyes, Theant2000, Ghane, Mindmatrix, Iromeister, RHaworth, Thorpe, Benbest, CKD, Cscott, Dglynch,
Meneth, Sega381, Viperious, Pinkgothic, Brownsteve, Scratchy, Marudubshinki, Sigkill, Graham87, Qwertyus, Yurik, Plau, Jclemens,
Phoenix-forgotten, Rjwilmsi, Koavf, Zbxgscqf, Teemu Maki~enwiki, Darguz Parsilvan, ErikHaugen, Gudeldar, Vegaswikian, Ttwaring,
Mikm, Husky, Lotu, Titoxd, StuartBrady, FlaBot, Mobus, Old Moonraker, Crazycomputers, Fragglet, AJR, Jeff02, Pathoschild, Gurch,
TheAnarcat, Intgr, Fresheneesz, John Maynard Friedman, Tylerl, Synchrite, Holmwood, Trejrco, Daev, Chobot, Adoniscik, Gwernol,
DanielDeGraaf, YurikBot, Wavelength, Borgx, Hawaiian717, Personman, Wester, Hairy Dude, Mukkakukaku, DMahalko, Zmding, Me
and, SeekerVI, Jengelh, SpuriousQ, Chaser, Pontillo, Eradt11, Akamad, Powerlord, Stephenb, Gaius Cornelius, Ihope127, Bovineone,
Wimt, Big Brother 1984, NawlinWiki, Arichnad, Daniel Luechtefeld, J128, Captkirk, Voidxor, Alex43223, EEMIV, Falcon9x5, Jeremy
Visser, Xpclient, Amigan, Graciella, Charu~enwiki, Closedmouth, Arthur Rubin, Shirishag75, Abune, Janto, Smurrayinchester, HereToHelp, Cmsb705, Smurfy, Allens, Snaxe920, LakeHMM, Benandorsqueaks, Carlosguitar, Yago~enwiki, Porttikivi, AndrewWTaylor,
Pankkake, DNSstuff, Subsurfer, SmackBot, Aigarius, Incnis Mrsi, Stux, Od Mishehu, Maian, Rrius, Wegesrand, Anastrophe, Mdd4696,
KelleyCook, Bugfood, Ohnoitsjamie, Folajimi, JoeKearney, Bluebot, Oliwan~enwiki, Bjaloudi, DocKrin, Jprg1966, Thumperward, Omniplex, Baa, SillyWilly, Philc 0780, Zsinj, Madman91, Frap, Nixeagle, OSborn, J-D-Cronin, Matchups, Kcordina, Midnightcomm, Wonderstruck, Rcloran, Napalm Llama, Cybercobra, MureninC, Mitar, Valenciano, Mr Minchin, MichaelBillington, Kasperd, Warren, Weregerbil,
Wisco, Luigi.a.cruz, Daniel.Cardenas, Tfl, Geekening, Andrei Stroe, TJJFV, ThurnerRupert, Weatherman1126, SashatoBot, Robomaeyhem, Gunnala, Crwth, Attys, Molerat, Zaphraud, Ninjagecko, Rait, Sosodank, BurnDownBabylon, Samantha of Cardyke, Breno, Rythie, Mathboy965, Zemyla, Michael miceli, Joshua Scott, IronGargoyle, BioTube, JHunterJ, Jec, JeroenMassar, Hvn0413, Stwalkerster,
DalZot, Muadd, Unclevinny, Aeluwas, Feureau, Infofarmer, Dicklyon, Ryulong, EdC~enwiki, Atakdoug, Saran945, Coaxial, Thrindel,
Kvng, Pjrm, PeterCScott, Teemuk, Parsmutaf, Sjrosen, Dwmalone, JoeBot, UncleDouggie, CapitalR, Und1sk0, Aeons, OlivierMehani,
Rocketman768, Benabik, DBooth, Bentendo24, Nicd, Artemgy, FatalError, CmdrObot, Geremia, PuerExMachina, Avanu, Nczempin,
Orchistro~enwiki, Smallpond, SelfStudyBuddy, Michael B. Trausch, Shultz IV, Skybon, MikeWren, Jbossbarr, Cydebot, Mblumber,
Boothy m, Endpoint, ST47, Skittleys, SymlynX, Verdy p, DumbBOT, M. B., Jr., Kozuch, Arbitrary username, Omicronpersei8, Wahjava, JodyB, Jhwoodyatt, Lagesag~enwiki, Drewheasman, Pietrodn, Hcberkowitz, Marek69, Vertium, Dontopenyoureyes, Wikimoder,
Davidhorman, Farncombe, Greg L, Kroneage, Sarutv~enwiki, Uruiamme, Dawnseeker2000, Marius p, Mentifisto, KrakatoaKatie, Fildon,
Hires an editor, AntiVandalBot, 49oxen, Wildboy211, Figz, Rps, Prolog, Autocracy, Edokter, Jj137, Dylan Lake, Credema, Dougher,
ZorphDark, NIXin, Caper13, SolarWind, JAnDbot, NapoliRoma, Sonicsuns, Andonic, AceJohnny, Cameltrader, Extropian314, HAl,
Enjoi4586, Olipro, DataMatrix, Magioladitis, VoABot II, PeterStJohn, Drearwig, Maxim Masiutin, Barri, Firealwaysworks, Robaire5006,
AlephGamma, 2345us, David Chouinard, Glenn burdett, A3nm, David Eppstein, Enquire, Kgfleischmann, Kestasjk, To Serve Man, Raffen,
Hdt83, MartinBot, FlieGerFaUstMe262, ChaosR, CableCat, Roadrunner7, Glrx, Pekaje, Thewallowmaker, Sibi antony, EdBever, Tgeairn,
Mange01, Trusilver, Alexander UA, Valvicus, Scj2315, Maurice Carbonaro, Public Menace, Agent00111, Jordipalet, WarthogDemon,
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Crd Alameda, Philip Trueman, Xandell, TXiKiBoT, Jreut, Paine, Sukenjain, A4bot, Naveenpf, Rei-bot, WikipedianYknOK, Xerces8,
Gekritzl, Don4of4, PaulTanenbaum, Jackfork, Ukh, Notbyworks, One half 3544, Likestheaction, Quaestor23, Jesin, Alainkaa, Belamp,
Falcon8765, Jddahl, Blaynew, Qwertytech, Andrew4u, Insanity Incarnate, SteveDavidsen, Logan, Darxus, Scottywong, Charliel 94, Kbrose,
Accountholder, SieBot, Dwandelt, Fnagaton, TJRC, Majordragon, Fewaffles, Nubiatech, GovStuff, Bazsa, Ovideon, X-Fi6, Yintan, Efreak, Kaypoh, Das7002, Rivardau, Ham Pastrami, Keilana, Joaosampaio, 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0 - hack,
Annesville, Itojun, Universalcosmos, Martyvis, Thehotelambush, Narellec, Bousquf, Mnudelman, Tmaufer, Xeltran, RSStockdale, Int21h,
OKBot, Svick, PassportDude, Jfromcanada, Kjtobo, MarkMLl, Axelriv, Djschaap, Fsterry, PabloStraub, Money23, Badcalculon, MenoBot,
Martarius, Sfan00 IMG, ClueBot, LP-mn, Zeerak88, TwoHundredOk, Watain, Brianmaddox, Jan1nad, Lawrence Cohen, Michaelrayw2,
Dlabtot, LUUSAP, Uncle Milty, ComputinChuck, Dylan620, Rgaushell, Puchiko, Auntof6, Pointillist, DerekMorr, Excirial, Sjmsteffann,
Lartoven, Jaizovic, M.O.X, Veriodbg, Intrepion, Dickguertin, Latifladid, Ejumper, Johnuniq, DumZiBoT, He6kd, XLinkBot, Defyant,
Ost316, Setherson, Prabhuhwiki, Addbot, Cantaloupe2, Some jerk on the Internet, Nacnud22032, HobbesLeviathan, Kattmamma, Ironholds, Scientus, Smarter1, Rilesman, Cst17, MrOllie, Suseno, NerdBoy1392, Glane23, Sandeepsoman, Jasper Deng, Hannes.nz, Lightbot, Tenth Plague, Ryuzaki00, Jarble, Quantumobserver, Simon J Kissane, Mro, Enduser, Team4Technologies, Ochib, Cloudmonkey,
Frnkblk, Legobot, Tedtoal, Luckas-bot, Yobot, Sobec, Sick bug, Bruce404, II MusLiM HyBRiD II, Crispmuncher, Becky Sayles, Mmxx,
South Bay, MihalOrela, AnomieBOT, KDS4444, Balachanderk, 1exec1, Обедающий философ, Utility Knife, Jo3sampl, Materialscientist,
Mhd.ashraf, MithrasPriest, Haleyga, Quebec99, LilHelpa, Madalibi, Xqbot, Rischmueller, Kthomas8, Jason.Singer, Reza 2638, Allanlw,
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12.2
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13
bulbcole, Jordandanford, Aschwegmann, Glen Hein, Nageh, Cgdallen, Thayts, SaveTheRbtz, Zygryk, Ryankearney, Corso84, JMilty, Citation bot 1, Galmicmi, OriumX, Scottbadman, I dream of horses, Pmokeefe, Mahtin, RedBot, Joncle, EdoDodo, Glenndavies, C.S.Abishek,
Cnwilliams, Fluffy 543, Hatu7, Jonkerz, Lotje, Bornapilot, Imzogelmo, Ralphcase, Dandorid, Kb966k, Tim Capps, Allen4names, Diannaa,
Minimac, DARTH SIDIOUS 2, TankMiche, TjBot, NameIsRon, Klaver, JeffMorriss, NerdyScienceDude, E94mli, EmausBot, Thexchair,
Jithrae, Terillius, Cal-linux, Freeaqingme, Jmv2009, Cesarolvera, Tommy2010, Jansenguus, Daonguyen95, Roy.wonder.cohen, The Nut,
Kiwi128, G-rocket, Tolly4bolly, TcomptonMA, Brandmeister, NYMets2000, Scott.somohano, MarkusWanner, Puffin, Spicemines, Thewolfchild, Cinnamondouche, AndyTheGrump, ClamDip, TYelliot, Teapeat, LVXN112, Ivolocy, Socialservice, Planetscared, Voomoo,
Mikhail Ryazanov, Rememberway, ClueBot NG, Gareth Griffith-Jones, PeterKz, Incompetence, MelbourneStar, Raghith, Lord Chamberlain, the Renowned, Joefromrandb, Jeffsw6, FGont, M00dawg, Mahuzu, CKerr1, Rezabot, Emonk72, Mormonsareloser, Rmartelloni,
No More TV, Widr, Antiqueight, Whatisipv6, Sgeeves, Vannessa.beth, Titodutta, 2001:db8, BG19bot, Deepeedoyle, Viniciustinti, The
Last Username I Could Think Of, Northamerica1000, Dialtoneapps, Gmedding, Dzlinker, Wiki13, Bsv109, Alangar Manickam, Badon,
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Sam, Nishu55, KasparBot, Mchaud10, Albaniakucov, Kholaa007 and Anonymous: 1288
12.2
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• File:Crystal_Clear_app_browser.png Source: https://upload.wikimedia.org/wikipedia/commons/f/fe/Crystal_Clear_app_browser.png
License: LGPL Contributors: All Crystal icons were posted by the author as LGPL on kde-look Original artist: Everaldo Coelho and
YellowIcon
• File:Ipv4_address.svg Source: https://upload.wikimedia.org/wikipedia/commons/7/74/Ipv4_address.svg License: Public domain Contributors: Own work Original artist: Indeterminate
• File:Ipv6_address_leading_zeros.svg Source: https://upload.wikimedia.org/wikipedia/commons/7/70/Ipv6_address_leading_zeros.svg
License: Public domain Contributors:
• Ipv6_address.svg Original artist: Ipv6_address.svg: Indeterminate
• File:Ipv6_header.svg Source: https://upload.wikimedia.org/wikipedia/commons/a/ab/Ipv6_header.svg License: CC BY-SA 3.0 Contributors: Own work Original artist: Mro
• File:Wikiversity-logo.svg Source: https://upload.wikimedia.org/wikipedia/commons/9/91/Wikiversity-logo.svg License: CC BY-SA 3.0
Contributors: Snorky (optimized and cleaned up by verdy_p) Original artist: Snorky (optimized and cleaned up by verdy_p)
12.3
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• Creative Commons Attribution-Share Alike 3.0
