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Wednesday, February 9, 2011
Conversion Table - Decimal, Hexadecimal, Octal, Binary
http://www.ascii.cl/conversion.htm
IP address
From Wikipedia, the free encyclopedia
(Redirected from Static IP)
For the Wikipedia user access level, see Wikipedia:User access levels#Anonymous users.
An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication.[1] An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."[2]The designers of the Internet Protocol defined an IP address as a 32-bit number[1] and this system, known as Internet Protocol Version 4 (IPv4), is still in use today. However, due to the enormous growth of the Internet and the predicted depletion of available addresses, a new addressing system (IPv6), using 128 bits for the address, was developed in 1995,[3] standardized as RFC 2460 in 1998,[4] and is being deployed world-wide since the mid-2000s.
IP addresses are binary numbers, but they are usually stored in text files and displayed in human-readable notations, such as 172.16.254.1 (for IPv4), and 2001:db8:0:1234:0:567:8:1 (for IPv6).
The Internet Assigned Numbers Authority (IANA) manages the IP address space allocations globally and delegates five regional Internet registries (RIRs) to allocate IP address blocks to local Internet registries (Internet service providers) and other entities.
Contents[hide] |
IP versions
Two versions of the Internet Protocol (IP) are in use: IP Version 4 and IP Version 6. (See IP version history for details.) Each version defines an IP address differently. Because of its prevalence, the generic term IP address typically still refers to the addresses defined by IPv4.IP version 4 addresses
Main article: IPv4#Addressing
IPv4 addresses are canonically represented in dot-decimal notation, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 172.16.254.1. Each part represents a group of 8 bits (octet) of the address. In some cases of technical writing, IPv4 addresses may be presented in various hexadecimal, octal, or binary representations.
IPv4 subnetting
In the early stages of development of the Internet Protocol,[1] network administrators interpreted an IP address in two parts: network number portion and host number portion. The highest order octet (most significant eight bits) in an address was designated as the network number and the remaining bits were called the rest field or host identifier and were used for host numbering within a network.This early method soon proved inadequate as additional networks developed that were independent of the existing networks already designated by a network number. In 1981, the Internet addressing specification was revised with the introduction of classful network architecture.[2]
Classful network design allowed for a larger number of individual network assignments and fine-grained subnetwork design. The first three bits of the most significant octet of an IP address were defined as the class of the address. Three classes (A, B, and C) were defined for universal unicast addressing. Depending on the class derived, the network identification was based on octet boundary segments of the entire address. Each class used successively additional octets in the network identifier, thus reducing the possible number of hosts in the higher order classes (B and C). The following table gives an overview of this now obsolete system.
| Class | Leading address bits | Range of first octet | Network ID format | Host ID format | Number of networks | Number of addresses |
|---|---|---|---|---|---|---|
| A | 0 | 0 - 127 | a | b.c.d | 27 = 128 | 224 = 16777216 |
| B | 10 | 128 - 191 | a.b | c.d | 214 = 16384 | 216 = 65536 |
| C | 110 | 192 - 223 | a.b.c | d | 221 = 2097152 | 28 = 256 |
Today, remnants of classful network concepts function only in a limited scope as the default configuration parameters of some network software and hardware components (e.g. netmask), and in the technical jargon used in network administrators' discussions.
IPv4 private addresses
Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be uniquely assigned to a particular computer or device. However, it was found that this was not always necessary as private networks developed and public address space needed to be conserved.Computers not connected to the Internet, such as factory machines that communicate only with each other via TCP/IP, need not have globally-unique IP addresses. Three ranges of IPv4 addresses for private networks were reserved in RFC 1918. These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry.
Today, when needed, such private networks typically connect to the Internet through network address translation (NAT).
| Start | End | No. of addresses | |
|---|---|---|---|
| 24-bit Block (/8 prefix, 1 × A) | 10.0.0.0 | 10.255.255.255 | 16777216 |
| 20-bit Block (/12 prefix, 16 × B) | 172.16.0.0 | 172.31.255.255 | 1048576 |
| 16-bit Block (/16 prefix, 256 × C) | 192.168.0.0 | 192.168.255.255 | 65536 |
IPv4 address exhaustion
Main article: IPv4 address exhaustion
IPv4 address exhaustion is the ultimate result of the decreasing supply of unallocated Internet Protocol Version 4 (IPv4) addresses available at the Internet Assigned Numbers Authority (IANA) and the regional Internet registries (RIRs) for assignment to end users and local Internet registries, such as Internet service providers. IPv4 provides for approximately 4.3 billion (232) addresses, divided into 256 /8 primary allocation blocks. IANA's primary address pool was exhausted on February 3, 2011 when the last 5 blocks were allocated to the 5 RIRs.[5][6] The first RIR to run out, APNIC, is expected to run out mid-2011[7].IP version 6 addresses
Main article: IPv6 address
The new design is not intended to provide a sufficient quantity of addresses on its own, but rather to allow efficient aggregation of subnet routing prefixes to occur at routing nodes. As a result, routing table sizes are smaller, and the smallest possible individual allocation is a subnet for 264 hosts, which is the square of the size of the entire IPv4 Internet. At these levels, actual address utilization rates will be small on any IPv6 network segment. The new design also provides the opportunity to separate the addressing infrastructure of a network segment — that is the local administration of the segment's available space — from the addressing prefix used to route external traffic for a network. IPv6 has facilities that automatically change the routing prefix of entire networks, should the global connectivity or the routing policy change, without requiring internal redesign or renumbering.
The large number of IPv6 addresses allows large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for efficient routing. With a large address space, there is not the need to have complex address conservation methods as used in Classless Inter-Domain Routing (CIDR).
Many modern desktop and enterprise server operating systems include native support for the IPv6 protocol, but it is not yet widely deployed in other devices, such as home networking routers, voice over IP (VoIP) and multimedia equipment, and network peripherals.
IPv6 private addresses
Just as IPv4 reserves addresses for private or internal networks, blocks of addresses are set aside in IPv6 for private addresses. In IPv6, these are referred to as unique local addresses (ULA). RFC 4193 sets aside the routing prefix fc00::/7 for this block which is divided into two /8 blocks with different implied policies (cf. IPv6) The addresses include a 40-bit pseudorandom number that minimizes the risk of address collisions if sites merge or packets are misrouted.Early designs (RFC 3513) used a different block for this purpose (fec0::), dubbed site-local addresses. However, the definition of what constituted sites remained unclear and the poorly defined addressing policy created ambiguities for routing. The address range specification was abandoned and must not be used in new systems.
Addresses starting with fe80:, called link-local addresses, are assigned to interfaces for communication on the link only. The addresses are usually automatically generated by the operating system for each network interface. This provides instant automatic network connectivity for any IPv6 host and means that if several hosts connect to a common hub or switch, they have an instant communication path via their link-local IPv6 address. This feature is used extensively, and invisibly to most users, in the lower layers of IPv6 network administration (cf. Neighbor Discovery Protocol).
None of the private address prefixes may be routed in the public Internet.
IP subnetworks
IP networks may be divided into subnetworks in both IPv4 and IPv6. For this purpose, an IP address is logically recognized as consisting of two parts: the network prefix and the host identifier, or interface identifier (IPv6). The subnet mask or the CIDR prefix determines how the IP address is divided into network and host parts.The term subnet mask is only used within IPv4. Both IP versions however use the Classless Inter-Domain Routing (CIDR) concept and notation. In this, the IP address is followed by a slash and the number (in decimal) of bits used for the network part, also called the routing prefix. For example, an IPv4 address and its subnet mask may be 192.0.2.1 and 255.255.255.0, respectively. The CIDR notation for the same IP address and subnet is 192.0.2.1/24, because the first 24 bits of the IP address indicate the network and subnet.
IP address assignment
Internet Protocol addresses are assigned to a host either anew at the time of booting, or permanently by fixed configuration of its hardware or software. Persistent configuration is also known as using a static IP address. In contrast, in situations when the computer's IP address is assigned newly each time, this is known as using a dynamic IP address.Methods
Static IP addresses are manually assigned to a computer by an administrator. The exact procedure varies according to platform. This contrasts with dynamic IP addresses, which are assigned either by the computer interface or host software itself, as in Zeroconf, or assigned by a server using Dynamic Host Configuration Protocol (DHCP). Even though IP addresses assigned using DHCP may stay the same for long periods of time, they can generally change. In some cases, a network administrator may implement dynamically assigned static IP addresses. In this case, a DHCP server is used, but it is specifically configured to always assign the same IP address to a particular computer. This allows static IP addresses to be configured centrally, without having to specifically configure each computer on the network in a manual procedure.In the absence or failure of static or stateful (DHCP) address configurations, an operating system may assign an IP address to a network interface using state-less auto-configuration methods, such as Zeroconf.
Uses of dynamic addressing
Dynamic IP addresses are most frequently assigned on LANs and broadband networks by Dynamic Host Configuration Protocol (DHCP) servers. They are used because it avoids the administrative burden of assigning specific static addresses to each device on a network. It also allows many devices to share limited address space on a network if only some of them will be online at a particular time. In most current desktop operating systems, dynamic IP configuration is enabled by default so that a user does not need to manually enter any settings to connect to a network with a DHCP server. DHCP is not the only technology used to assign dynamic IP addresses. Dialup and some broadband networks use dynamic address features of the Point-to-Point Protocol.Sticky dynamic IP address
A sticky dynamic IP address is an informal term used by cable and DSL Internet access subscribers to describe a dynamically assigned IP address that seldom changes. The addresses are usually assigned with the DHCP protocol. Since the modems are usually powered-on for extended periods of time, the address leases are usually set to long periods and simply renewed upon expiration. If a modem is turned off and powered up again before the next expiration of the address lease, it will most likely receive the same IP address.[edit] Address autoconfiguration
RFC 3330 defines an address block, 169.254.0.0/16, for the special use in link-local addressing for IPv4 networks. In IPv6, every interface, whether using static or dynamic address assignments, also receives a local-link address automatically in the fe80::/10 subnet.These addresses are only valid on the link, such as a local network segment or point-to-point connection, that a host is connected to. These addresses are not routable and like private addresses cannot be the source or destination of packets traversing the Internet.
When the link-local IPv4 address block was reserved, no standards existed for mechanisms of address autoconfiguration. Filling the void, Microsoft created an implementation that is called Automatic Private IP Addressing (APIPA). Due to Microsoft's market power, APIPA has been deployed on millions of machines and has, thus, become a de facto standard in the industry. Many years later, the IETF defined a formal standard for this functionality, RFC 3927, entitled Dynamic Configuration of IPv4 Link-Local Addresses.
Uses of static addressing
Some infrastructure situations have to use static addressing, such as when finding the Domain Name System(DNS) host that will translate domain names to IP addresses. Static addresses are also convenient, but not absolutely necessary, to locate servers inside an enterprise. An address obtained from a DNS server comes with a time to live, or caching time, after which it should be looked up to confirm that it has not changed. Even static IP addresses do change as a result of network administration (RFC 2072)Public addresses
A public IP address in common parlance is synonymous with a, globally routable unicast IP address.[citation needed]Both IPv4 and IPv6 define address ranges that are reserved for private networks and link-local addressing. The term public IP address often used exclude these types of addresses.
Modifications to IP addressing
IP blocking and firewalls
Firewalls perform Internet Protocol blocking to protect networks from unauthorized access. They are common on today's Internet. They control access to networks based on the IP address of a client computer. Whether using a blacklist or a whitelist, the IP address that is blocked is the perceived IP address of the client, meaning that if the client is using a proxy server or network address translation, blocking one IP address may block many individual computers.IP address translation
Multiple client devices can appear to share IP addresses: either because they are part of a shared hosting web server environment or because an IPv4 network address translator (NAT) or proxy server acts as an intermediary agent on behalf of its customers, in which case the real originating IP addresses might be hidden from the server receiving a request. A common practice is to have a NAT hide a large number of IP addresses in a private network. Only the "outside" interface(s) of the NAT need to have Internet-routable addresses.[8]Most commonly, the NAT device maps TCP or UDP port numbers on the outside to individual private addresses on the inside. Just as a telephone number may have site-specific extensions, the port numbers are site-specific extensions to an IP address.
In small home networks, NAT functions usually take place in a residential gateway device, typically one marketed as a "router". In this scenario, the computers connected to the router would have 'private' IP addresses and the router would have a 'public' address to communicate with the Internet. This type of router allows several computers to share one public IP address.
[edit] Diagnostic tools
Computer operating systems provide various diagnostic tools to examine their network interface and address configuration. Windows provides the command-line interface tools ipconfig and netsh and users of Unix-like systems can use ifconfig, netstat, route, lanstat, ifstat, or iproute2 utilities to accomplish the task.See also
- Address pool
- Classful network
- Geolocation
- Geolocation software
- Hierarchical name space
- hostname: a human-readable alpha-numeric designation that may map to an IP address
- Internet service provider
- IP address spoofing
- IP blocking
- IP Multicast
- List of assigned /8 IPv4 address blocks
- MAC address
- Ping
- Private network
- Provider-aggregatable address space
- Provider-independent address space
- Regional Internet Registry
- Subnet address
- Virtual IP address
- WHOIS
References
- ^ a b c RFC 760, DOD Standard Internet Protocol (January 1980)
- ^ a b RFC 791, Internet Protocol - DARPA Internet Program Protocol Specification (September 1981)
- ^ a b RFC 1883, Internet Protocol, Version 6 (IPv6) Specification, S. Deering, R. Hinden (December 1995)
- ^ a b RFC 2460, Internet Protocol, Version 6 (IPv6) Specification, padnda'srockS. Deering, R. Hinden, The Internet Society (December 1998)
- ^ Smith, Lucie; Lipner, Ian (3 February 2011). "Free Pool of IPv4 Address Space Depleted". Number Resource Organization. Retrieved 3 February 2011.
- ^ ICANN,nanog mailing list. "Five /8s allocated to RIRs - no unallocated IPv4 unicast /8s remain".
- ^ "Two /8s allocated to APNIC from IANA". APNIC. 2010-01-01. Retrieved 2011-02-03.
- ^ Comer, Douglas (2000). Internetworking with TCP/IP:Principles, Protocols, and Architectures -- 4th ed.. Upper Saddle River, NJ: Prentice Hall. p. 394. ISBN 0-13-018380-6.
External links
Subnet Cheat Sheet
http://krow.net/dict/subnet.html
Subnet Cheat Sheet
| Hosts | Netmask | Amount of a Class C | |
|---|---|---|---|
| /30 | 4 | 255.255.255.252 | 1/64 |
| /29 | 8 | 255.255.255.248 | 1/32 |
| /28 | 16 | 255.255.255.240 | 1/16 |
| /27 | 32 | 255.255.255.224 | 1/8 |
| /26 | 64 | 255.255.255.192 | 1/4 |
| /24 | 256 | 255.255.255.0 | 1 |
| /23 | 512 | 255.255.254.0 | 2 |
| /22 | 1024 | 255.255.252.0 | 4 |
| /21 | 2048 | 255.255.248.0 | 8 |
| /20 | 4096 | 255.255.240.0 | 16 |
| /19 | 8192 | 255.255.224.0 | 32 |
| /18 | 16384 | 255.255.192.0 | 64 |
| /17 | 32768 | 255.255.128.0 | 128 |
| /16 | 65536 | 255.255.0.0 | 256 |
Guide to sub-class C blocks
/25 -- 2 Subnets -- 126 Hosts/Subnet
| /30 -- 64 Subnets -- 2 Hosts/Subnet
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/26 -- 4 Subnets -- 62 Hosts/Subnet
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/27 -- 8 Subnets -- 30 Hosts/Subnet
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/28 -- 16 Subnets -- 14 Hosts/Subnet
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/29 -- 32 Subnets -- 6 Hosts/Subnet
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Subnetwork
From Wikipedia, the free encyclopedia
All computers that belong to a subnet are addressed with a common, identical, most-significant bit-group in their IP address. This results in the logical division of an IP address into two fields, a network or routing prefix and the rest field. The rest field is a specific identifier for the computer or the network interface.
The routing prefix is expressed in CIDR notation. It is written as the first address of a network followed by the bit-length of the prefix, separated by a slash (/) character. For example, 192.168.1.0/24 is the prefix of the Internet Protocol Version 4 network starting at the given address, having 24 bits allocated for the network prefix, and the rest (8 bits) reserved for host addressing. The IPv6 address specification 2001:db8::/32 is a large network for 296 hosts, having a 32-bit routing prefix. In IPv4 the routing prefix is also specified in the form of the subnet mask, which is expressed in quad-dotted decimal representation like an address. For example, 255.255.255.0 is the network mask for the 192.168.1.0/24 prefix.
Traffic between subnetworks is interchanged with special gateway computers called routers; they constitute logical or physical borders between the subnets.
The benefits of subnetting vary with each deployment scenario. In the address allocation architecture of the Internet using Classless Inter-Domain Routing (CIDR) and in large organizations, it is necessary to allocate address space efficiently. It may also enhance routing efficiency, or have advantages in network management when subnetworks are administratively controlled by different entities in a larger organization. Subnets may be arranged logically in a hierarchical architecture, partitioning an organization's network address space into a tree-like routing structure.
Contents[hide] |
[edit] Network addressing and routing
Computers participating in a network such as the Internet each have at least one logical address. Usually this address is unique to each device and can either be configured dynamically from a network server, statically by an administrator, or automatically by stateless address autoconfiguration.An address fulfills the functions of identifying the host and locating it on the network. The most common network addressing architecture is Internet Protocol version 4 (IPv4), but its successor, IPv6 is in early deployment stages. An IPv4 address consists of 32 bits, for human readability written in a form consisting of four decimal octets separated by full stops (dots), called dot-decimal notation. An IPv6 address consists of 128 bits written in a hexadecimal notation and grouping 16 bits separated by colons.
For the purpose of network management, an IP address is logically divided into two fields, a network prefix and the rest field. All hosts on a subnetwork have the same network prefix. This routing prefix occupies the most-significant bits of the address. The number of bits allocated within a network to the internal routing prefix may vary between subnets, depending on the network architecture. While in IPv6 the prefix must consist of a set of contiguous 1-bits, in IPv4 this is not enforced, albeit no efficiency is gained. The rest field is a unique local identification and is either a host number on the local network or an interface identifier.
This logical addressing structure permits the selective routing of IP packets across multiple networks via special gateway computers, called routers, to a destination host if the network prefixes of origination and destination hosts differ, or sent directly to a target host on the local network if they are the same. Routers constitute logical or physical borders between the subnets, and manage traffic between them. Each subnet is served by a designated default router, but may consist internally of multiple physical Ethernet segments interconnected by network switches or network bridges.
The routing prefix of an address is written in a form identical to that of the address itself. This is called the network mask, or netmask, of the address. For example, a specification of the most-significant 18 bits of an IPv4 address,
11111111.11111111.11000000.00000000, is written as 255.255.192.0. If this mask designates a subnet within a larger network, it is also called the subnet mask. This form of denoting the network mask, however, is only used for IPv4 networks.The modern standard form of specification of the network prefix, used for both IPv4 and IPv6, counts the number of bits in the prefix and appends that number to the address with a slash (/) separator:
- 192.168.0.0, netmask 255.255.0.0 is written as 192.168.0.0/16
- In IPv6, 2001:db8::/32 designates the address 2001:db8:: and its network prefix consisting of the most significant 32 bits.
In classful networking in IPv4, prior to the introduction of CIDR, the network prefix could be directly obtained from the IP address, based on its highest order bit sequence. This determined the class (A, B, C) of the address and therefore the network mask. Since the introduction of CIDR, however, assignment of an IP address to a network interface requires two parameters, the address and its network mask.
In IPv4, on-link determination for an IP address is given simply by the address and netmask configuration, as the address cannot be disassociated from the on-link prefix.[2] For IPv6, however, on-link determination is different in detail and requires the Neighbor Discovery Protocol (NDP).[3][4] IPv6 address assignment to an interface carries no requirement of a matching on-link prefix and vice versa, with the exception of link-local addresses.
While subnetting may improve network performance in an organizational network, it increases routing complexity, since each locally connected subnet must be represented by a separate entry in the routing tables of each connected router. However, by careful design of the network, routes to collections of more distant subnets within the branches of a tree-hierarchy can be aggregated by single routes. Variable-length subnet masking (VLSM) functionality in commercial routers made the introduction of CIDR seamless across the Internet and in enterprise networks.
IPv4 subnetting
The process of subnetting involves the separation of the network and subnet portion of an address from the host identifier. This is performed by a bitwise AND operation between the IP address and the (sub)network prefix. The result yields the network address or prefix, and the remainder is the host identifier.Determining the network prefix
An IPv4 network mask consist of 32 bits, a sequence of ones (1) followed by a block of 0s. The last block of zeros (0) designate that part as being the host identifier.The following example shows the separation of the network prefix and the host identifier from an address (192.168.5.130) and its associated /24 network mask (255.255.255.0). The operation is visualized in a table using binary address formats.
| Binary form | Dot-decimal notation | |
|---|---|---|
| IP address | 11000000.10101000.00000101.10000010 | 192.168.5.130 |
| Subnet mask | 11111111.11111111.11111111.00000000 | 255.255.255.0 |
| Network prefix | 11000000.10101000.00000101.00000000 | 192.168.5.0 |
| Host part | 00000000.00000000.00000000.10000010 | 0.0.0.130 |
Subnetting
Subnetting is the process of designating some high-order bits from the host part and grouping them with the network mask to form the subnet mask. This divides a network into smaller subnets. The following diagram modifies the example by moving two bits from the host part to the subnet mask to form a smaller subnet one fourth the previous size:| Binary form | Dot-decimal notation | |
|---|---|---|
| IP address | 11000000.10101000.00000101.10000010 | 192.168.5.130 |
| Subnet mask | 11111111.11111111.11111111.11000000 | 255.255.255.192 |
| Network prefix | 11000000.10101000.00000101.10000000 | 192.168.5.128 |
| Host part | 00000000.00000000.00000000.00000010 | 0.0.0.2 |
Special addresses and subnets
Internet Protocol version 4 uses specially designated address formats to facilitate recognition of special address functionality. The first and the last subnets obtained by subnetting have traditionally had a special designation and, early on, special usage implications.[5] In addition, IPv4 uses the all ones host address, i.e. the last address within a network, for broadcast transmission to all hosts on the link.Subnet zero and the all-ones subnet
The first subnet obtained from subnetting has all bits in the subnet bit group set to zero (0). It is therefore called subnet zero.[6] The last subnet obtained from subnetting has all bits in the subnet bit group set to one (1). It is therefore called the all-ones subnet.[7]The IETF discouraged the production use of these two subnets at one point due to possible confusion of having a network and subnet with the same address.[8] The practice of avoiding subnet zero and the all-ones subnet was declared obsolete in 1995 by RFC 1878, an informational, but now historical RFC.[9]
Subnet and host counts
The number of subnetworks available, and the number of possible hosts in a network may be readily calculated. In the example (above) two bits were borrowed to create subnetworks, thus creating 4 (22) possible subnets.| Network | Network (binary) | Broadcast address |
|---|---|---|
192.168.5.0/26 | 11000000.10101000.00000101.00000000 | 192.168.5.63 |
192.168.5.64/26 | 11000000.10101000.00000101.01000000 | 192.168.5.127 |
192.168.5.128/26 | 11000000.10101000.00000101.10000000 | 192.168.5.191 |
192.168.5.192/26 | 11000000.10101000.00000101.11000000 | 192.168.5.255 |
The remaining bits after the subnet are used for addressing hosts within the subnet. In the above example the subnet mask consists of 26 bits, leaving 6 bits for the host identifier. This allows for 64 combinations (26), however the all zeros value and all ones value are reserved for the network ID and broadcast address respectively, leaving 62 addresses.
In general the number of available hosts on a subnet is 2n−2, where n is the number of bits used for the host portion of the address.
RFC 3021 specifies an exception to this rule when dealing with 31-bit subnet masks (i.e. 1-bit host identifiers). In such networks, usually point-to-point links, only two hosts (the end points) may be connected and a specification of network and broadcast addresses is not necessary.
A /24 network may be divided into the following subnets by increasing the subnet mask successively by one bit. This affects the total number of hosts that can be addressed in the /24 network (last column).
| CIDR notation | Network mask | Available subnets | Available hosts per subnet | Total usable hosts |
|---|---|---|---|---|
| /24 | 255.255.255.0 | 1 | 254 | 254 |
| /25 | 255.255.255.128 | 2 | 126 | 252 |
| /26 | 255.255.255.192 | 4 | 62 | 248 |
| /27 | 255.255.255.224 | 8 | 30 | 240 |
| /28 | 255.255.255.240 | 16 | 14 | 224 |
| /29 | 255.255.255.248 | 32 | 6 | 192 |
| /30 | 255.255.255.252 | 64 | 2 | 128 |
| /31 | 255.255.255.254 | 128 | 2 * | 256 |
IPv6 subnetting
The design of the IPv6 address space differs significantly from IPv4. The primary reason for subnetting in IPv4 is to improve efficiency in the utilization of the relatively small address space available, particularly to enterprises. No such limitations exist in IPv6, as the address space available, even to end-users, is large.An IPv6 subnet always has 64 bits in its host portion. It therefore has a /64 routing prefix (128−64 = the 64 most-significant bits). Although it is technically possible to use smaller subnets,[citation needed] they are impractical for local area networks because stateless address auto configuration of network interfaces (RFC 4862) requires a /64 address. The Internet Engineering Task Force recommends to use /64 subnets even for point-to-point links, which consists of only the two end hosts.
The recommended allocation for an IPv6 customer site is an address space of 80 address bits (prefix /48).[10] This provides 65536 subnets for a site. Despite this recommendation, other common allocations are /56 (72 bits) as well as /64 prefixes for a residential customer network.
IPv6 does not implement special address formats for broadcast traffic or network numbers, and thus all addresses in a subnet are valid host addresses.
Subnetting in IPv6 is based on the concepts of variable-length subnet masking (VLSM) and the Classless Inter-Domain Routing methodology. It is used to route traffic between the global allocation spaces and within customer network between subnets and the larger Internet.
See also
- IPv4 subnetting reference
- IPv6 subnetting reference
- Classless Inter-Domain Routing
- Classful network
- Autonomous System
References
- ^ RFC 950, Internet Standard Subnetting Procedure, J. Mogul, J. Postel (August 1985), page 1, 16
- ^ RFC 1122, Requirements for Internet Hosts -- Communication Layers, Section 3.3.1, R. Braden, IETF (October 1989)
- ^ RFC 4861, Neighbor Discovery for IP version 6 (IPv6), T. Narten et al. (September 2007)
- ^ RFC 5942, IPv6 Subnet Model: The Relationship between Links and Subnet Prefixes, H. Singh, W. Beebee, E. Nordmark (July 2010)
- ^ "Document ID 13711 - Subnet Zero and the All-Ones Subnet". Cisco Systems, Inc.. 2005-08-10. Retrieved 2010-04-25. "Traditionally, it was strongly recommended that subnet zero and the all-ones subnet not be used for addressing. [...] Today, the use of subnet zero and the all-ones subnet is generally accepted and most vendors support their use."
- ^ "Document ID 13711 - Subnet Zero and the All-Ones Subnet". Cisco Systems, Inc.. 2005-08-10. Retrieved 2010-04-23. "the first [...] subnet[...], known as subnet zero"
- ^ "Document ID 13711 - Subnet Zero and the All-Ones Subnet". Cisco Systems, Inc.. 2005-08-10. Retrieved 2010-04-23. "[...] the last subnet[...], known as [...] the all-ones subnet"
- ^ Jeffrey Mogul; Jon Postel (August 1985). [RFC 950 "Internet Standard Subnetting Procedure"]. Internet Engineering Task Force (IETF). p. 6. Retrieved 2010-04-23. "It is useful to preserve and extend the interpretation of these special addresses in subnetted networks. This means the values of all zeros and all ones in the subnet field should not be assigned to actual (physical) subnets."
- ^ Troy Pummill; Bill Manning (December 1995). [RFC 1878 "Variable Length Subnet Table For IPv4"]. "This practice is obsolete! Modern software will be able to utilize all definable networks." Note: RFC 1878 is an Informational RFC, and has been demoted to category Historic.
- ^ "IPv6 Addressing Plans". ARIN IPv6 Wiki. Retrieved 2010-04-25. "All customers get one /48 unless they can show that they need more than 65k subnets. [...] If you have lots of consumer customers you may want to assign /56s to private residence sites."
Further reading
- RFC 1812 Requirements for IPv4 Routers
- RFC 917 Utility of subnets of Internet networks
- RFC 1101 DNS Encodings of Network Names and Other Type
- Blank, Andrew G. TCP/IP Foundations Technology Fundamentals for IT Success. San Francisco, London: Sybex, Copyright 2004.
- Lammle, Todd. CCNA Cisco Certified Network Associate Study Guide 5th Edition. San Francisco, London: Sybex, Copyright 2005.
- Groth, David and Toby Skandier. Network + Study Guide, 4th Edition. San Francisco, London: Wiley Publishing, Inc., Copyright 2005.
External links
- "Understanding IP Addressing - Everything You Ever Wanted To Know" (PDF). 3COM. May 2001. pp. 76 pages. "1.08 MB"
- IP Address Subnetting Tutorial
- Cisco-IP Addressing and Subnetting for New Users
- IP subnetting made easy
- Subnetworking at the Open Directory Project
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