Misplaced Pages

#752247

41-556: An IPv6 client embeds the IPv4 address it wishes to communicate with using the host part of the IPv6 network segment, resulting in an IPv4-embedded IPv6 addresses (hence the 32-bit address space in the IPv6 network segment), and sends packets to the resulting address. The NAT64 gateway creates a mapping between the IPv6 and the IPv4 addresses, which may be manually configured or determined automatically. A simple NAT64 installation may consist of

82-520: A block contains 2 = 2 addresses. The smaller the length of the network prefix, the larger the block: a / 21 block is 8 times larger than a / 24 block. Colon (:) characters in IPv6 addresses may conflict with the established syntax of resource identifiers, such as URIs and URLs . The colon is conventionally used to terminate the host path before a port number . To alleviate this conflict, literal IPv6 addresses are enclosed in square brackets in such resource identifiers, for example: When

123-476: A broadcast address may be received by all network-attached hosts. In contrast, a multicast address is used to address a specific group of devices, and a unicast address is used to address a single device. For network layer communications, a broadcast address may be a specific IP address . At the data link layer on Ethernet networks, it is a specific MAC address . In Internet Protocol version 4 ( IPv4 ) networks, broadcast addresses are special values in

164-415: A different host in each of those zones. Even if a single address is not in use in different zones, the address prefixes for addresses in those zones may still be identical, which makes the operating system unable to select an outgoing interface based on the information in the routing table (which is prefix-based). In order to resolve the ambiguity in textual addresses, a zone index must be appended to

205-703: A gateway with two interfaces connected to an IPv4 network and an IPv6 network, respectively. Traffic from the IPv6 network is routed via the gateway which performs all the necessary translations for transferring packets between the two networks. However, the translation is not symmetric, as the IPv6 address space is much larger than the IPv4 address space; thus, one-to-one address mapping is not possible. The gateway maintains IPv6-to-IPv4 address mapping, which may be established with an automatic algorithm (stateless mapping) or with special and manual translations (stateful mapping) when

246-447: A given LAN segment if they are addressed to MAC address FF:FF:FF:FF:FF:FF . Ethernet frames that contain IP broadcast packages are usually sent to this address. Ethernet broadcasts are used, among other purposes, by Address Resolution Protocol to resolve IP addresses to MAC addresses. Internetwork Packet Exchange (IPX) allows broadcast. A packet with network number of FFFFFFFF

287-489: A group of interfaces, usually belonging to different nodes. A packet sent to an anycast address is delivered to just one of the member interfaces, typically the nearest host, according to the routing protocol's definition of distance. Anycast addresses cannot be identified easily, they have the same format as unicast addresses, and differ only by their presence in the network at multiple points. Almost any unicast address can be employed as an anycast address. A multicast address

328-513: A mixed addressing environment. For such use cases, a special notation has been introduced, which expresses IPv4-mapped and IPv4-compatible IPv6 addresses by writing the least-significant 32 bits of an address in the familiar IPv4 dot-decimal notation , whereas the 96 most-significant bits are written in IPv6 format. For example, the IPv4-mapped IPv6 address ::ffff:c000:0280 is written as ::ffff:192.0.2.128 , thus expressing clearly

369-476: A subnet but, for security reasons, many routers disable the forwarding of these by default. A special definition exists for the IP address 255.255.255.255 . It is the broadcast address of the zero network or 0.0.0.0 , which in Internet Protocol standards stands for this network , i.e. the local network. Transmission to this address is limited by definition, in that it is never forwarded by

410-399: A vastly enlarged address space . IPv6 addresses are classified by the primary addressing and routing methodologies common in networking: unicast addressing, anycast addressing, and multicast addressing. A unicast address identifies a single network interface. The Internet Protocol delivers packets sent to a unicast address to that specific interface. An anycast address is assigned to

451-626: A zone. As multiple interfaces may belong to the same zone (e.g. when connected to the same network), in practice two addresses with different zone identifiers may actually be equivalent, and refer to the same host on the same link. When used in uniform resource identifiers (URI), the use of the percent sign causes a syntax conflict, therefore it must be escaped via percent-encoding , e.g.: In Microsoft Windows operating systems, IPv4 addresses are valid location identifiers in Uniform Naming Convention (UNC) path names. However,

SECTION 10

#1732800978753

492-406: Is also used by multiple hosts that acquire the multicast address destination by participating in the multicast distribution protocol among the network routers. A packet that is sent to a multicast address is delivered to all interfaces that have joined the corresponding multicast group. IPv6 does not implement broadcast addressing . Broadcast's traditional role is subsumed by multicast addressing to

533-644: Is designed to be used when the communication is initiated by IPv6 hosts. Some mechanisms, including static address mapping, exist to allow the inverse scenario. Not every type of resource is accessible with NAT64. Protocols that embed IPv4 literal addresses, such as SIP and SDP , FTP , WebRTC , Skype , MSN, and any other content with IPv4 literals are excluded, but a dual-stacked web proxy allows IPv6-only clients to access even web pages with IPv4 literals in URLs. However, 464XLAT , which uses NAT64, allows use of such protocols over IPv6-only connections. For SIP and FTP,

574-458: Is the only syntax on Microsoft Windows , but as support for this syntax is mandatory per standard, it is also available on other operating systems. BSD-based operating systems (including macOS) also support an alternative, non-standard syntax, where a numeric zone index is encoded in the second 16-bit word of the address. E.g.: In all operating systems mentioned above, the zone index for link-local addresses actually refers to an interface, not to

615-476: The / 48 routing prefix. A link-local address is also based on the interface identifier, but uses a different format for the network prefix. The prefix field contains the binary value 1111111010. The 54 zeroes that follow make the total network prefix the same for all link-local addresses ( fe80:: / 64 link-local address prefix ), rendering them non-routable. Multicast addresses are formed according to several specific formatting rules, depending on

656-479: The all-nodes link-local multicast group ff02::1 . However, the use of the all-nodes group is not recommended, and most IPv6 protocols use protocol-specific link-local multicast groups to avoid disturbing every interface on a given network. An IPv6 address consists of 128 bits. For each of the major addressing and routing methodologies, various address formats are recognized by dividing the 128 address bits into bit groups and using established rules for associating

697-495: The host identifier portion of the address (any bit positions which hold a 0 in the subnet mask) to 1. As shown in the example below, in order to calculate the directed broadcast address to transmit a packet to an entire IPv4 subnet using the private IP address space 172.16.0.0 / 12 , which has the subnet mask 255.240.0.0 , the broadcast address is calculated as 172.16.0.0 bitwise ORed with 0.15.255.255 = 172.31.255.255 . Directed broadcasts always work within

738-415: The modified EUI-64 format, but this method is now not recommended for privacy reasons. ) Unique local addresses are addresses analogous to IPv4 private network addresses. The prefix field contains the binary value 1111110. The L bit is one for locally assigned addresses; the address range with L set to zero is currently not defined. The random field is chosen randomly once, at the inception of

779-502: The packet header to indicate the source and the destination of each packet. The IP address of the destination is used to make decisions about routing IP packets to other networks. IPv6 is the successor to the first addressing infrastructure of the Internet , Internet Protocol version 4 (IPv4). In contrast to IPv4, which defined an IP address as a 32-bit value, IPv6 addresses have a size of 128 bits. Therefore, in comparison, IPv6 has

820-523: The IETF has defined a canonical format for rendering IPv6 addresses in text: These methods can lead to very short representations for IPv6 addresses. For example, the localhost (loopback) address, 0:0:0:0:0:0:0:1 , and the IPv6 unspecified address, 0:0:0:0:0:0:0:0 , are reduced to ::1 and :: , respectively. During the transition of the Internet from IPv4 to IPv6, it is typical to operate in

861-458: The URL also contains a port number the notation is: where the trailing 443 is the example's port number. For addresses with other than global scope (as described in § Address scopes ), and in particular for link-local addresses, the choice of the network interface for sending a packet may depend on which zone the address belongs to. The same address may be valid in different zones, and in use by

SECTION 20

#1732800978753

902-424: The address. The zone index is separated from the address by a percent sign (%). Although numeric zone indices must be universally supported, the zone index may also be an implementation-dependent string. The link-local address could be expressed by or The former (using an interface name) is customary on most Unix -like operating systems (e.g., BSD , Linux , macOS ). The latter (using an interface number)

943-468: The all-hosts address, though; instead, they send and receive on particular link-local multicast addresses. This results in higher efficiency because network hosts can filter traffic based on multicast address and do not need to process all broadcasts or all-hosts multicasts. Broadcast is possible also on the underlying data link layer in Ethernet networks. Frames are addressed to reach every computer on

984-434: The all-ones host address of each subnet is that subnet's directed broadcast address . The directed broadcast address for any IPv4 host can be obtained by taking the bit complement (bitwise NOT) of the subnet mask and then performing a bitwise OR operation with the host's IP address. A shortcut to this process (for common masks using only 0 and 1 bit placements) is to simply take the host's IP address and set all bits in

1025-457: The application. For all multicast addresses, the prefix field holds the binary value 11111111. Currently, three of the four flag bits in the flg field are defined; the most-significant flag bit is reserved for future use. The four-bit scope field ( sc ) is used to indicate where the address is valid and unique. In addition, the scope field is used to identify special multicast addresses, like solicited node . The sc(ope) field holds

1066-586: The binary value 0010 (link-local). Solicited-node multicast addresses are computed as a function of a node's unicast or anycast addresses. A solicited-node multicast address is created by copying the last 24 bits of a unicast or anycast address to the last 24 bits of the multicast address. Link-scoped multicast addresses use a comparable format. An IPv6 address is represented as eight groups of four hexadecimal digits, each group representing 16 bits The groups are separated by colons (:). An example of an IPv6 address is: The standards provide flexibility in

1107-458: The colon is an illegal character in a UNC path name. Thus, the use of IPv6 addresses is also illegal in UNC names. For this reason, Microsoft implemented a transcription algorithm to represent an IPv6 address in the form of a domain name that can be used in UNC paths. For this purpose, Microsoft registered and reserved the second-level domain ipv6-literal.net on the Internet (although they gave up

1148-405: The configuration of an interface with address 2001:db8:a::123 connected to subnet 2001:db8:a:: / 64 is written as 2001:db8:a::123 / 64 . The size of a block of addresses is specified by writing a slash (/) followed by a number in decimal whose value is the length of the network prefix in bits. For example, an address block with 48 bits in the prefix is indicated by / 48 . Such

1189-434: The destination back to the source. Anycast addresses are syntactically identical to and indistinguishable from unicast addresses. Their only difference is administrative. Scopes for anycast addresses are therefore the same as for unicast addresses. Broadcast address A broadcast address is a network address used to transmit to all devices connected to a multiple-access communications network . A message sent to

1230-488: The directly attached network. Unique local addresses have global scope, but they are not globally administered. As a result, only other hosts in the same administrative domain (e.g., an organization), or within a cooperating administrative domain are able to reach such addresses, if properly routed. As their scope is global, these addresses are valid as a source address when communicating with any other global-scope address, even though it may be impossible to route packets from

1271-481: The domain in January 2014 ). IPv6 addresses are transcribed as a hostname or subdomain name within this namespace , in the following fashion: is written as This notation is automatically resolved locally by Microsoft software, without any queries to DNS name servers. If the IPv6 address contains a zone index, it is appended to the address portion after an 's' character: is written as Every IPv6 address, except

NAT64 - Misplaced Pages Continue

1312-437: The first address in the block (ending in all zeroes), a slash (/), and a decimal value equal to the size in bits of the prefix. For example, the network written as 2001:db8:1234:: / 48 starts at address 2001:db8:1234:0000:0000:0000:0000:0000 and ends at 2001:db8:1234:ffff:ffff:ffff:ffff:ffff . The routing prefix of an interface address may be directly indicated with the address using CIDR notation. For example,

1353-455: The first packet from the IPv6 network reaches the NAT64 gateway. Stateless translation is appropriate when a NAT64 translator is used in front of IPv6-only servers to allow them to be reached by remote IPv4-only clients. Stateful translation is suitable for deployment at the client side or at the service provider, allowing IPv6-only client hosts to reach remote IPv4-only nodes. In general, NAT64

1394-474: The host-identification part of an IP address . The all-ones value was established as the standard broadcast address for networks that support broadcast. This method of using the all-ones address was first proposed by R. Gurwitz and R. Hinden in 1982. The later introduction of subnets and Classless Inter-Domain Routing changed this slightly, so that the all-ones value becomes the local broadcast address and

1435-449: The original IPv4 address that was mapped to IPv6. An IPv6 network uses an address block that is a contiguous group of IPv6 addresses of a size that is a power of two . The leading set of bits of the addresses are identical for all hosts in a given network, and are called the network's address or routing prefix . Network address ranges are written in CIDR notation . A network is denoted by

1476-461: The problem can also be solved using an application-level gateway , or using Port Control Protocol with the PREFIX64 extension. IPv6 address An Internet Protocol version 6 address ( IPv6 address ) is a numeric label that is used to identify and locate a network interface of a computer or a network node participating in a computer network using IPv6 . IP addresses are included in

1517-476: The representation of IPv6 addresses. The full representation of eight four-digit groups may be simplified by several techniques, eliminating parts of the representation. In general, representations are shortened as much as possible. However, this practice complicates several common operations, namely searching for a specific address or an address pattern in text documents or streams, and comparing addresses to determine equivalence. For mitigation of these complications,

1558-421: The routers connecting the local network to other networks. IP broadcasts are used by BOOTP and DHCP clients to find and send requests to their respective servers. Internet Protocol version 6 ( IPv6 ) does not implement this method of broadcast, and therefore does not define broadcast addresses. Instead, IPv6 uses multicast addressing to the all-hosts multicast group. No IPv6 protocols are defined to use

1599-417: The routing prefix may vary; a larger prefix size means a smaller subnet ID size. The bits of the subnet ID field are available to the network administrator to define subnets within the given network. The 64-bit interface identifier is automatically established randomly, obtained from a DHCPv6 server, or assigned manually. (Historically, it was automatically generated from the interface's MAC address using

1640-589: The unspecified address ( :: ), has a scope , which specifies in which part of the network it is valid. For unicast addresses, two scopes are defined: link-local and global. Link-local addresses and the loopback address have link-local scope, which means they can only be used on a single directly attached network. All other addresses (including unique local addresses ) have global (or universal ) scope, which means they are potentially globally routable and can be used to connect to addresses with global scope anywhere, or to addresses with link-local scope on

1681-417: The values of these bit groups with special addressing features. Unicast and anycast addresses are typically composed of two logical parts: a 64-bit network prefix used for routing , and a 64-bit interface identifier used to identify a host's network interface. The network prefix (the routing prefix combined with the subnet ID ) is contained in the most significant 64 bits of the address. The size of

NAT64 - Misplaced Pages Continue

#752247