Internet Protocol version 4 (IPv4) is the fourth iteration of the Internet Protocol (IP) and it is the first version of the protocol to be widely deployed. IPv4 is the dominant network layer protocol on the Internet and apart from IPv6 it is the only standard internetwork-layer protocol used on the Internet. In computing and telecommunications, the transport layer is the second highest layer in the four and five layer TCP/IP reference models, where it responds to service requests from the application layer and issues service requests to the Internet layer. ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. ... The Datagram Congestion Control Protocol (DCCP) is a message-oriented transport layer protocol that is currently under development in the IETF. Applications that might make use of DCCP include those with timingconstraints on the delivery of data such that reliable in-order delivery, when combined with congestion control, is likely... In the field of computer networking, the IETF Signaling Transport (SIGTRAN) working group defined the Stream Control Transmission Protocol (SCTP) as a transport layer protocol in 2000. ... The Resource ReSerVation Protocol (RSVP), described in RFC 2205, is a Transport layer protocol designed to reserve resources across a network for an integrated services Internet. ... Network congestion avoidance is a process used in computer networks to avoid congestion. ... The network layer is third layer out of seven in OSI model and it is the third layer out of five in TCP/IP model. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... Internet Protocol version 6 (IPv6) is a network layer for packet-switched internetworks. ... The Open Shortest Path First (OSPF) protocol is a hierarchical interior gateway protocol (IGP) for routing in Internet Protocol, using a link-state in the individual areas that make up the hierarchy. ... Is Is is Yeah Yeah Yeahs third EP, to be released on July 24, 2007. ... The Border Gateway Protocol (BGP) is the core routing protocol of the Internet. ... IPsec (IP security) is a suite of protocols for securing Internet Protocol (IP) communications by authenticating and/or encrypting each IP packet in a data stream. ... In computer networking, the Address Resolution Protocol (ARP) is the standard method for finding a hosts hardware address when only its network layer address is known. ... Reverse Address Resolution Protocol (RARP) is a network layer protocol used to obtain an IP address for a given hardware address (such as an Ethernet address). ... This article is chiefly about the Routing Information Protocol (RIP) for the Internet Protocol, but also discusses some other routing information protocols. ... The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet protocol suite. ... The ICMP for IPv6 (Internet Control Message Protocol Version 6) is an integral part of the IPv6 architecture and must be completely supported by all IPv6 implementations. ... The Internet Group Management Protocol (IGMP) is a communications protocol used to manage the membership of Internet Protocol multicast groups. ... This article does not cite any references or sources. ... IEEE 802. ... The IEEE 802. ... Wi-Fi (IPA: ) is the common name for a popular wireless technology used in home networks, mobile phones, video games and more. ... Official WiMax logo WiMAX, the Worldwide Interoperability for Microwave Access, is a telecommunications technology aimed at providing wireless data over long distances in a variety of ways, from point-to-point links to full mobile cellular type access. ... Asynchronous Transfer Mode (ATM) is a cell relay, packet switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ... Dynamic synchronous Transfer Mode , or DTM for short, is a network protocol. ... Token-Ring local area network (LAN) technology was developed and promoted by IBM in the early 1980s and standardised as IEEE 802. ... Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ... In computer networking, fiber-distributed data interface (FDDI) is a standard for data transmission in a local area network that can extend in range up to 200 km (124 miles). ... In the context of computer networking, frame relay consists of an efficient data transmission technique used to send digital information quickly and cheaply in a relay of frames to one or many destinations from one or many end-points. ... General Packet Radio Service (GPRS) is a Mobile Data Service available to users of Global System for Mobile Communications (GSM) and IS-136 mobile phones. ... Evolution-Data Optimized or Evolution-Data only, abbreviated as EV-DO or EVDO and often EV, is one telecommunications standard for the wireless transmission of data through radio signals, typically for broadband Internet access. ... High-Speed Packet Access (HSPA) is a collection of mobile telephony protocols that extend and improve the performance of existing UMTS protocols. ... High-Level Data Link Control (HDLC) is a bit-oriented synchronous data link layer protocol developed by the International Organization for Standardization (ISO). ... In computing, the Point-to-Point Protocol, or PPP, is commonly used to establish a direct connection between two nodes. ... The Point-to-Point Tunneling Protocol (PPTP) is a method for implementing virtual private networks. ... In computer networking, the Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol used to support virtual private networks (VPNs). ... ISDN redirects here. ... ARCNET (also CamelCased as ARCnet, an acronym from Attached Resource Computer NETwork) is a local area network (LAN) protocol, similar in purpose to Ethernet or Token Ring. ... Link Layer Topology Discovery (LLTD) is a licensed data link layer protocol for network topology discovery and quality of service diagnostics, developed by Microsoft as part of their Windows Rally set of technologies. ... This article does not cite any references or sources. ... The Ethernet physical layer is the physical layer component of the Ethernet standard. ... RS-232 (also referred to as EIA RS-232C or V.24) is a standard for serial binary data interchange between a DTE (Data terminal equipment) and a DCE (Data communication equipment). ... Synchronous optical networking, is a method for communicating digital information using lasers or light-emitting diodes (LEDs) over optical fiber. ... There are very few or no other articles that link to this one. ... Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length. ... Coaxial Cable For the weapon, see coaxial weapon. ... 25 Pair Color Code Chart 10BASE-T UTP Cable Twisted pair cabling is a common form of wiring in which two conductors are wound around each other for the purposes of cancelling out electromagnetic interference known as crosstalk. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... The network layer is third layer out of seven in OSI model and it is the third layer out of five in TCP/IP model. ... Internet Protocol version 6 (IPv6) is a network layer for packet-switched internetworks. ...

It is described in IETF RFC 791 (September 1981) which made obsolete RFC 760 (January 1980). The United States Department of Defense also standardized it as MIL-STD-1777. The Internet Engineering Task Force (IETF) is charged with developing and promoting Internet standards. ... The United States Department of Defense (DOD or DoD) is the federal department charged with coordinating and supervising all agencies and functions of the government relating directly to national security and the military. ...

IPv4 is a data-oriented protocol to be used on a packet switched internetwork (e.g., Ethernet). It is a best effort protocol in that it does not guarantee delivery. It does not make any guarantees on the correctness of the data; this may result in duplicated packets or packets delivered out of order. These aspects are addressed by an upper layer protocol (e.g. TCP, and partly by UDP). In computer networking and telecommunications, packet switching is a communications paradigm in which packets (messages or fragments of messages) are individually routed between nodes, with no previously established communication path. ... This article is about the Internet An internet is a more general term for any set of interconnected computer networks that are connected by internetworking Graphic representation of the WWW information network structure around Wikipedia, as represented by hyperlinks The Internet, or simply the Net, is the publicly available worldwide... Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ... Best effort delivery describes a network service in which the network does not provide any guarantees that data is delivered or that a user is given a guaranteed quality of service level or a certain priority. ... In computer networking, the upper layer protocol (ULP) refers to the more abstract protocol when performing encapsulation. ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. ...

Addressing

Internet addressing growth map.

IPv4 uses 32-bit (four-byte) addresses, which limits the address space to 4,294,967,296 (2³²) possible unique addresses. However, some are reserved for special purposes such as private networks (~18 million addresses) or multicast addresses (~16 million addresses). This reduces the number of addresses that can be allocated as public Internet addresses. As the number of addresses available are consumed, an IPv4 address shortage appears to be inevitable, however Network Address Translation (NAT) has significantly delayed this inevitability. This article is about the unit of information. ... For the computer industry magazine, see Byte (magazine). ... In computing, an address space defines a range of discrete addresses, each of which may correspond to a physical or virtual memory register, a network host, peripheral device, disk sector or other logical or physical entity. ... It has been suggested that RFC 1918 be merged into this article or section. ... Multicast is sometimes also (incorrectly) used to refer to a multiplexed broadcast. ... In computer networking, Network Address Translation (NAT, also known as Network Masquerading, Native Address Translation or IP Masquerading) is a technique of transceiving network traffic through a router that involves re-writing the source and/or destination IP addresses and usually also the TCP/UDP port numbers of IP packets...

This limitation has helped stimulate the push towards IPv6, which is currently in the early stages of deployment and is currently the only contender to replace IPv4. Internet Protocol version 6 (IPv6) is a network layer for packet-switched internetworks. ...

Address representations

When writing IPv4 addresses in human-readable form, the most common notation is the dot-decimal notation. There are other notations based on the values of 200.100 in the dot-decimal notation which comprises four octets in decimal separated by periods. This is the base format used in the conversion in the following table: Dot-decimal notation is a method of expressing octets using base-10 rather than hexadecimal. ... For other uses, see Decimal (disambiguation). ...

Most of these formats should work in all browsers. Additionally, in dotted format, each octet can be of any of the different bases. For example, 192.0x00.0002.235 is a valid (though unconventional) equivalent to the above addresses. Dot-decimal notation is a method of expressing octets using base-10 rather than hexadecimal. ... In mathematics and computer science, hexadecimal, base-16, or simply hex, is a numeral system with a radix, or base, of 16, usually written using the symbols 0–9 and A–F, or a–f. ... For other uses, see Decimal (disambiguation). ... The octal numeral system, or oct for short, is the base-8 number system, and uses the digits 0 to 7. ...

A final form is not really a notation since it is rarely written in an ASCII string notation. That form is a binary form of the hexadecimal notation in binary. This difference is merely the representational difference between the string "0xCF8E83EB" and the 32-bit integer value 0xCF8E83EB. This form is used for assigning the source and destination fields in a software program. Computer software (or simply software) refers to one or more computer programs and data held in the storage of a computer for some purpose. ...

Allocation

Originally, an IP address was divided into two parts:

• Network ID: first octet
• Host ID: last three octets

This created an upper limit of 256 networks. As the networks began to be allocated, this was soon seen to be inadequate.

To overcome this limit, different classes of network were defined, in a system which later became known as classful networking. Five classes were created (A, B, C, D, and E), three of which (A, B, and C) had different lengths for the network field. The rest of an address was used to identify a host within a network, which meant that each network class had a different maximum number of hosts. Thus there were a few networks with each having many host addresses and numerous networks with each only having a few host addresses. Class D was for multicast addresses and Class E was reserved. Classful networking is the name given to the first round of changes to the structure of the IP address in IPv4. ... Multicast is sometimes also (incorrectly) used to refer to a multiplexed broadcast. ...

Around 1993, these classes were replaced with a Classless Inter-Domain Routing (CIDR) scheme, and the previous scheme was dubbed "classful", by contrast. CIDR's primary advantage is to allow re-division of Class-A, -B and -C networks so that smaller (or larger) blocks of addresses may be allocated to various entities (such as Internet service providers, or their customers) or local area networks. Year 1993 (MCMXCIII) was a common year starting on Friday (link will display full 1993 Gregorian calendar). ... Warning! This Article contains disinformation. ... “ISP” redirects here. ...

The actual assignment of an address is not arbitrary. The fundamental principle of routing is that the address of a device encodes information about a the device's location within a network. This implies that an address assigned to one part of a network will not function in another part of the network. A hierarchical structure, created by CIDR and overseen by the Internet Assigned Numbers Authority (IANA) and its Regional Internet Registries (RIRs), manages the assignment of Internet addresses worldwide. Each RIR maintains a publicly-searchable WHOIS database that provides information about IP address assignments; information from these databases plays a central role in numerous tools that attempt to locate IP addresses geographically. This article is about routing in computer networks. ... The Internet Assigned Numbers Authority (IANA) is the entity that oversees global IP address allocation, DNS root zone management, and other Internet protocol assignments. ... A Regional Internet Registry (RIR) is an organisation overseeing the allocation and registration of Internet number resources within a particular region of the world. ... WHOIS is a TCP-based query/response protocol which is widely used for querying a database in order to determine the owner of a domain name, an IP address, or an autonomous system number on the Internet. ...

Warning! This Article contains disinformation. ... It has been suggested that RFC 1918 be merged into this article or section. ... This article is about the loopback device IP address. ... Zeroconf or Zero Configuration Networking is a set of techniques that automatically create a usable IP network without configuration or special servers. ... It has been suggested that RFC 1918 be merged into this article or section. ... Internet Protocol version 6 (IPv6) is a network layer for packet-switched internetworks. ... It has been suggested that RFC 1918 be merged into this article or section. ... Multicast is sometimes also (incorrectly) used to refer to a multiplexed broadcast. ...

Private networks

Main article: private network

Of the four billion addresses allowed in IPv4, four ranges of address are reserved for private networking use only. These ranges are not routable outside of private networks, and private machines cannot directly communicate with public networks. They can, however, do so through network address translation. It has been suggested that RFC 1918 be merged into this article or section. ... It has been suggested that RFC 1918 be merged into this article or section. ... In computer networking, Network Address Translation (NAT, also known as Network Masquerading, Native Address Translation or IP Masquerading) is a technique of transceiving network traffic through a router that involves re-writing the source and/or destination IP addresses and usually also the TCP/UDP port numbers of IP packets...

The following are the four ranges reserved for private networks:

The ranges 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are reserved for private networking by RFC 1918, while the 169.254.0.0/16 range is reserved for Link-Local addressing as defined in RFC 3927. Classful networking is the name given to the first round of changes to the structure of the IP address in IPv4. ... Warning! This Article contains disinformation. ... Zeroconf or Zero Configuration Networking is a set of techniques that automatically create a usable IP network without configuration or special servers. ...

Localhost

Main article: localhost

In addition to private networking, the address range 127.0.0.0–127.255.255.255 (or 127.0.0.0/8 in CIDR notation) is reserved for localhost communication. Any address within this range should never appear on an actual network and any packet sent to this address does not leave the source computer, and will appear as an incoming packet on that computer (known as loopback). This article is about the loopback device IP address. ... Warning! This Article contains disinformation. ... This article is about the loopback device IP address. ... A loopback is a communications channel with only one endpoint. ...

Addresses ending in 0 or 255

Main article: IPv4 subnetting reference

It is a common misconception that addresses ending in 255 or 0 can never be assigned to hosts, but this is only true of networks with subnet masks of at least 24 bits — Class C networks in the old classful addressing scheme, or in CIDR, networks with masks of /24 to /32 (or 255.255.255.0–255.255.255.255). Certain chunks of IPv4 address space are specially allocated by RFCs for special uses such as loopback (RFC 1643), Private networks (RFC 1918), and Zeroconf (RFC 3927) usage, and are not available for allocation by Regional Internet Registries (RIRs). ...

In classful addressing (now obsolete with the advent of CIDR), there are only three possible subnet masks: Class A, 255.0.0.0 or /8; Class B, 255.255.0.0 or /16; and Class C, 255.255.255.0 or /24. For example, in the subnet 192.168.5.0/255.255.255.0 (or 192.168.5.0/24) the identifier 192.168.5.0 refers to the entire subnet, so it cannot also refer to an individual device in that subnet. Warning! This Article contains disinformation. ...

A broadcast address is an address that allows information to be sent to all machines on a given subnet rather than a specific machine. Generally, the broadcast address is found by taking the bit complement of the subnet mask and then OR-ing it bitwise with the network identifier. More simply, the broadcast address is the last address in the range belonging to the subnet. In our example, the broadcast address would be 192.168.5.255, so to avoid confusion this address also cannot be assigned to a host. On a Class-A, -B, or -C subnet, the broadcast address would always end in 255. In computer networking, a broadcast address is an IP address that allows information to be sent to all machines on a given subnet rather than a specific machine. ...

However, this does not mean that every addresses ending in 255 cannot be used as a host address. For example, in the case of a Class B subnet 192.168.0.0/255.255.0.0 (or 192.168.0.0/16), equivalent to the address range 192.168.0.0–192.168.255.255, the broadcast address is 192.168.255.255. However, one can assign 192.168.1.255, 192.168.2.255, etc. (though this can cause confusion). Also, 192.168.0.0 is the network identifier and so cannot be assigned, but 192.168.1.0, 192.168.2.0, etc. can be assigned (though this can also cause confusion).

With the advent of CIDR, broadcast addresses do not necessarily end with 255.

In general, the first and last addresses in a subnet are used as the network identifier and broadcast address, respectively. All other addresses in the subnet can be assigned to hosts on that subnet.

Resolving

Main article: Domain Name System

Hosts on the Internet are usually known not by IP addresses but by names (e.g., www.wikipedia.org, www.whitehouse.gov, www.freebsd.org, www.berkeley.edu). The routing of IP packets across the Internet is not connected to such names. This requires translating (or resolving) names to addresses. The Domain Name System (DNS) associates various sorts of information with domain names; most importantly, it serves as the phone book for the Internet by translating human-readable computer hostnames, e. ...

The Domain Name System (DNS) provides such a system to convert names to addresses and addresses to names. Much like CIDR addressing, the DNS naming is also hierarchical and allows for subdelegation of name spaces to other DNS servers. The Domain Name System (DNS) associates various sorts of information with domain names; most importantly, it serves as the phone book for the Internet by translating human-readable computer hostnames, e. ... Warning! This Article contains disinformation. ...

Think of this in a similar way to how you find a phone number. You want to call The Acme Bakers but don't know the number. You ring directory enquiries and they tell you the number you need to dial or can even connect you. Next you might want to call Acme Builder. Again, you only need to know the phone number of directory enquiries, they will almost always have the number you want and connect you. Only if you ask directory enquiries for the number of a company which doesn't exist will they say they can't connect you - similar to a DNS error in your web browser.

Exhaustion

Main article: IP address exhaustion

Since the 1980s, there has been concern that the number of available IP(v4) addresses is being exhausted. This was the driving factor in classful networks and then later in the creation of CIDR addressing. IP address exhaustion refers to the decreasing availability of publicly available IPv4 IP addresses. ... Classful networking is the name given to the first round of changes to the structure of the IP address in IPv4. ... Warning! This Article contains disinformation. ...

Today, there are several driving forces to the next address allocation solution:

• Mobile devices — laptop computers, PDAs, mobile phones
• Always-on devices — ADSL modems, cable modems
• Rapidly growing number of Internet users

The most visible solution is to migrate to IPv6 since the address size jumps dramatically from 32 bits to 128 bits, which would allow each of about 18 quintillion people their own set of 18 quintillion addresses (3.4e38 total addresses). However, migration has proved to be a challenge in itself, and total Internet adoption of IPv6 is unlikely to occur for many years. Laptop with touchpad. ... User with Treo (PDA with smartphone functionality) Personal digital assistants (PDAs) are handheld computers, but have become much more versatile over the years. ... Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ... An outdated model of the Motorola Surfboard cable modem A cable modem is a type of modem that provides access to a data signal sent over the cable television infrastructure. ... Internet Protocol version 6 (IPv6) is a network layer for packet-switched internetworks. ... Main article: Names of large numbers A quintillion is a number written as either: a 1 followed by 18 zeros (10 to the 18th power, as used in the short scale system of numeration. ...

Some things that can be done to mitigate the IPv4 address exhaustion are (not mutually exclusive):

• Network address translation (NAT)
• Use of private networks
• Dynamic Host Configuration Protocol (DHCP)
• Name-based virtual hosting
• Tighter control by Regional Internet Registries on the allocation of addresses to Local Internet Registries
• Network renumbering to reclaim large blocks of address space allocated in the early days of the Internet

As of April 2008, predictions of exhaustion date of the unallocated IANA pool seem to converge to between May 2011^[2] and February 2010.^[3] In computer networking, Network Address Translation (NAT, also known as Network Masquerading, Native Address Translation or IP Masquerading) is a technique of transceiving network traffic through a router that involves re-writing the source and/or destination IP addresses and usually also the TCP/UDP port numbers of IP packets... It has been suggested that RFC 1918 be merged into this article or section. ... DHCP redirects here. ... It has been suggested that this article or section be merged into shared web hosting service. ... A Regional Internet Registry (RIR) is an organisation overseeing the allocation and registration of Internet number resources within a particular region of the world. ...

Network address translation

Main article: Network address translation

One method to increase both address utilization and security is to use network address translation (NAT). With NAT, assigning one address to a public machine as an internet gateway and using a private network for an organization's computers allows for considerable address savings. This also increases security by making the computers on a private network not directly accessible from the public network. In computer networking, Network Address Translation (NAT, also known as Network Masquerading, Native Address Translation or IP Masquerading) is a technique of transceiving network traffic through a router that involves re-writing the source and/or destination IP addresses and usually also the TCP/UDP port numbers of IP packets... In computer networking, Network Address Translation (NAT, also known as Network Masquerading, Native Address Translation or IP Masquerading) is a technique of transceiving network traffic through a router that involves re-writing the source and/or destination IP addresses and usually also the TCP/UDP port numbers of IP packets... This article is about the Internet An internet is a more general term for any set of interconnected computer networks that are connected by internetworking Graphic representation of the WWW information network structure around Wikipedia, as represented by hyperlinks The Internet, or simply the Net, is the publicly available worldwide... In telecommunications, the term gateway has the following meanings: In a communications network, a network node equipped for interfacing with another network that uses different protocols. ... It has been suggested that RFC 1918 be merged into this article or section. ...

Virtual private networks

Main article: Virtual private network

Since private address ranges are deliberately ignored by all public routers, it is not normally possible to connect two private networks (e.g., two branch offices) via the public Internet. Virtual private networks (VPNs) solve this problem. VPN redirects here. ... VPN redirects here. ...

VPNs work by inserting an IP packet (encapsulated packet) directly into the data field of another IP packet (encapsulating packet) and using a publicly routable address in the encapsulating packet. Once the VPN packet is routed across the public network and reaches the endpoint, the encapsulated packet is extracted and then transmitted on the private network just as if the two private networks were directly connected.

Optionally, the encapsulated packet can be encrypted to secure the data while over the public network (see VPN article for more details).

Address Resolution Protocol

Main article: Address Resolution Protocol

IP is a protocol associated with the network layer and deals heavily with logical addressing schemes (i.e., IP addresses). If node A on network 1 sends a packet (which includes the source and destination IP) of information across a segmented network to node B on network 2, the interconnecting network device(s) — such as a switch, which has addressing tables that are dynamically populated — must be able to resolve a node's physical MAC address to its logical IP address in order for it to forward that packet to the destination IP address. This discovery and mapping of IP addresses to hardware (MAC) addresses is accomplished through Address Resolution Protocol (ARP) messages, which are always executed as a network layer broadcast. Once the mapping has been made, it is stored in the switch's addressing/routing table for a specified amount of time, otherwise known as TTL, for future use. In computer networking, the Address Resolution Protocol (ARP) is the standard method for finding a hosts hardware address when only its network layer address is known. ... The network layer is third layer out of seven in OSI model and it is the third layer out of five in TCP/IP model. ... A network switch is a computer networking device that connects network segments. ... In computer networking, the Address Resolution Protocol (ARP) is the standard method for finding a hosts hardware address when only its network layer address is known. ... Time to live (sometimes abbreviated TTL) is a limit on the period of time or number of iterations or transmissions in computer and computer network technology that a unit of data (e. ...

Reverse Address Resolution Protocol/DHCP

Main articles: Reverse Address Resolution Protocol, BOOTP, and Dynamic Host Configuration Protocol

Unlike the situation outlined for ARP, the case arises when a computer knows its data link layer address but not its IP address. This is a common scenario in private networks and Digital Subscriber Line (DSL) connections when the IP addresses of the machines are irrelevant. This is usually the case for work stations but not servers. Reverse Address Resolution Protocol (RARP) is a network layer protocol used to obtain an IP address for a given hardware address (such as an Ethernet address). ... In computing, BOOTP, short for Bootstrap Protocol, is a UDP network protocol used by a network client to obtain its IP address automatically. ... DHCP redirects here. ... This article does not cite any references or sources. ... It has been suggested that RFC 1918 be merged into this article or section. ... DSL redirects here. ... In telecommunication, the term work station has the following meanings: 1. ... In information technology, a server is an application or device that performs services for connected clients as part of a client-server architecture. ...

RARP is an obsoleted method for answering this question: “This is my hardware address; what is my IP address?” RARP was replaced by BOOTP which, in turn, was replaced by Dynamic Host Configuration Protocol (DHCP). In computing, BOOTP, short for Bootstrap Protocol, is a UDP network protocol used by a network client to obtain its IP address automatically. ... DHCP redirects here. ...

In addition to assigning an IP address, DHCP can also assign an NTP server, DNS servers, and more. The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. ... The Domain Name System (DNS) associates various sorts of information with domain names; most importantly, it serves as the phone book for the Internet by translating human-readable computer hostnames, e. ...

Packet structure

An IP packet consists of a header section and a data section.

Header

The header consists of 13 fields, of which only 12 are required. The 13^th field is optional (red background in table) and aptly named: options. The fields in the header are packed with the most significant byte first (big endian), and for the diagram and discussion, the most significant bits are considered to come first. The most significant bit is numbered 0, so the version field is actually found in the four most significant bits of the first byte, for example. In computing, endianness is the byte (and sometimes bit) ordering in memory used to represent some kind of data. ...

Version 

The first header field in an IP packet is the four-bit version field. For IPv4, this has a value of 4 (hence the name IPv4).

Internet Header Length (IHL) 

The second field is a four-bit Internet Header Length (IHL) telling the number of 32-bit words in the header. Since an IPv4 header may contain a variable number of options, this field specifies the size of the header (this also coincides with the offset to the data). The minimum value for this field is 5 (rfc791), which is a length of 5×32 = 160 bits. Being a four-bit field, the maximum length is 15 words or 480 bits.

Type of Service (TOS) 

In RFC 791, the following eight bits were allocated to a Type of Service (TOS) field:

• bits 0–2: precedence (111 - Network Control, 110 - Internetwork Control, 101 - CRITIC/ECP, 100 - Flash Override, 011 - Flash, 010 - Immediate, 001 - Priority, 000 - Routine)
• bit 3: 0 = Normal Delay, 1 = Low Delay
• bit 4: 0 = Normal Throughput, 1 = High Throughput
• bit 5: 0 = Normal Reliability, 1 = High Reliability
• bits 6–7: Reserved for future use

This field is now used for DiffServ and ECN. The original intention was for a sending host to specify a preference for how the datagram would be handled as it made its way through an internet. For instance, one host could set its IPv4 datagrams' TOS field value to prefer low delay, while another might prefer high reliability. In practice, the TOS field has not been widely implemented. However, a great deal of experimental, research and deployment work has focused on how to make use of these eight bits. These bits have been redefined, most recently through DiffServ working group in the IETF and the Explicit Congestion Notification codepoints (see RFC 3168). New technologies are emerging that require real-time data streaming and therefore will make use of the TOS field. An example is Voice over IP (VoIP) that is used for interactive data voice exchange.

Total Length 

This 16-bit field defines the entire datagram size, including header and data, in bytes. The minimum-length datagram is 20 bytes (20-byte header + 0 bytes data) and the maximum is 65,535 — the maximum value of a 16-bit word. The minimum size datagram that any host is required to be able to handle is 576 bytes, but most modern hosts handle much larger packets. Sometimes subnetworks impose further restrictions on the size, in which case datagrams must be fragmented. Fragmentation is handled in either the host or packet switch in IPv4 (see Fragmentation and reassembly).

Identification 

This field is an identification field and is primarily used for uniquely identifying fragments of an original IP datagram. Some experimental work has suggested using the ID field for other purposes, such as for adding packet-tracing information to datagrams in order to help trace back datagrams with spoofed source addresses.

Flags 

A three-bit field follows and is used to control or identify fragments. They are (in order, from high order to low order):

• Reserved; must be zero. As an April Fools joke, proposed for use in RFC 3514 as the "Evil bit".
• Don't Fragment (DF)
• More Fragments (MF)

If the DF flag is set and fragmentation is required to route the packet then the packet will be dropped. This can be used when sending packets to a host that does not have sufficient resources to handle fragmentation.

When a packet is fragmented all fragments have the MF flag set except the last fragment, which does not have the MF flag set. The MF flag is also not set on packets that are not fragmented — an unfragmented packet is its own last fragment.

Fragment Offset 

The fragment offset field, measured in units of eight-byte blocks, is 13 bits long and specifies the offset of a particular fragment relative to the beginning of the original unfragmented IP datagram. The first fragment has an offset of zero. This allows a maximum offset of 65,528 () which would exceed the maximum IP packet length of 65,535 with the header length included.

Time To Live (TTL) 

An eight-bit time to live (TTL) field helps prevent datagrams from persisting (e.g. going in circles) on an internet. Historically the TTL field limited a datagram's lifetime in seconds, but has come to be a hop count field. Each packet switch (or router) that a datagram crosses decrements the TTL field by one. When the TTL field hits zero, the packet is no longer forwarded by a packet switch and is discarded. Typically, an ICMP message (specifically the time exceeded) is sent back to the sender that it has been discarded. The reception of these ICMP messages is at the heart of how traceroute works.

Protocol 

This field defines the protocol used in the data portion of the IP datagram. The Internet Assigned Numbers Authority maintains a list of Protocol numbers and were originally defined in RFC 790. Common protocols and their decimal values are shown below (see Data).

Header Checksum 

The 16-bit checksum field is used for error-checking of the header. At each hop, the checksum of the header must be compared to the value of this field. If a header checksum is found to be mismatched, then the packet is discarded. Note that errors in the data field are up to the encapsulated protocol to handle — indeed, both UDP and TCP have checksum fields.

Since the TTL field is decremented on each hop and fragmentation is possible at each hop then at each hop the checksum will have to be recomputed. The method used to compute the checksum is defined within RFC 791:

The checksum field is the 16-bit one's complement of the one's complement sum of all 16-bit words in the header. For purposes of computing the checksum, the value of the checksum field is zero.

In other words, all 16-bit words are summed together using one's complement (with the checksum field set to zero). The sum is then one's complemented and this final value is inserted as the checksum field.

Source address 

An IPv4 address is a group of four eight-bit octets for a total of 32 bits. The value for this field is determined by taking the binary value of each octet and concatenating them together to make a single 32-bit value.

For example, the address 10.9.8.7 (00001010.00001001.00001000.00000111 in binary) would be 00001010000010010000100000000111.

This address is the address of the sender of the packet. Note that this address may not be the "true" sender of the packet due to network address translation. Instead, the source address will be translated by the NATing machine to its own address. Thus, reply packets sent by the receiver are routed to the NATing machine, which translates the destination address to the original sender's address.

Destination address 

Identical to the source address field but indicates the receiver of the packet.

Options 

Additional header fields may follow the destination address field, but these are not often used. Note that the value in the IHL field must include enough extra 32-bit words to hold all the options (plus any padding needed to ensure that the header contains an integral number of 32-bit words). The list of options may be terminated with an EOL (End of Options List) option; this is only necessary if the end of the options would not otherwise coincide with the end of the header. The possible options that can be put in the header are as follows:

• Note: the Copied, Option Class, and Option Number are sometimes referred to as a single eight-bit field - the Option Type.

The use of the LSRR and SSRR options (Loose and Strict Source and Record Route) is discouraged because they create security concerns; many routers block packets containing these options.

This article does not cite any references or sources. ... Network congestion avoidance is a process used in computer networks to avoid congestion. ... In information technology, a packet is a formatted block of data carried by a packet mode computer network. ... In computing, word is a term for the natural unit of data used by a particular computer design. ... This article does not cite any references or sources. ... Network congestion avoidance is a process used in computer networks to avoid congestion. ... DiffServ or differentiated services is a method of trying to guarantee quality of service on large networks such as the Internet. ... Network congestion avoidance is a process used in computer networks to avoid congestion. ... An overview of how VoIP works A typical analog telephone adapter for connecting an ordinary phone to a VoIP network Ciscos implementation of VoIP - IP Phone Voice over Internet Protocol, also called VoIP (pronounced voyp), IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband is the... A graphic representation of relationships and source of the various variables representing a chunk of C subnets In computer networks, a subnetwork or subnet is a range of logical addresses within the address space that is assigned to an organization. ... The evil bit is a fictional IP packet header field proposed in RFC 3514, a humorous April 1st RFC from 2003 authored by Steve Bellovin. ... Time to live (sometimes abbreviated TTL) is a limit on the period of time or number of iterations or transmissions in computer and computer network technology that a unit of data (e. ... In telecommunication, the term hop count has the following meanings: In a data communications network, the number of legs traversed by a packet between its source and destination. ... This article is about a computer networking device. ... The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet protocol suite. ... The Time Exceeded Message is an ICMP message which is generated by a gateway to inform the source of a datagram that the datagram has been discarded due to the time to live field reaching zero. ... traceroute outputs the list of traversed routers in simple text format, together with timing information traceroute is a computer network tool used to determine the route taken by packets across an IP network. ... The Internet Assigned Numbers Authority (IANA) is the entity that oversees global IP address allocation, DNS root zone management, and other Internet protocol assignments. ... A checksum is a form of redundancy check, a simple way to protect the integrity of data by detecting errors in data that are sent through space (telecommunications) or time (storage). ... User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... In mathematics, signed numbers in some arbitrary base is done in the usual way, by prefixing it with a - sign. ... In computer networking, Network Address Translation (NAT, also known as Network Masquerading, Native Address Translation or IP Masquerading) is a technique of transceiving network traffic through a router that involves re-writing the source and/or destination IP addresses and usually also the TCP/UDP port numbers of IP packets...

Data

The last field is not a part of the header and, consequently, not included in the checksum field. The contents of the data field are specified in the protocol header field and can be any one of the transport layer protocols. In computing and telecommunications, the transport layer is the second highest layer in the four and five layer TCP/IP reference models, where it responds to service requests from the application layer and issues service requests to the Internet layer. ...

Some of the most commonly used protocols are listed below including their value used in the protocol field:

• 1: Internet Control Message Protocol (ICMP)
• 2: Internet Group Management Protocol (IGMP)
• 6: Transmission Control Protocol (TCP)
• 17: User Datagram Protocol (UDP)
• 89: Open Shortest Path First (OSPF)
• 132: Stream Control Transmission Protocol (SCTP)

See List of IPv4 protocol numbers for a complete list. The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet protocol suite. ... The Internet Group Management Protocol (IGMP) is a communications protocol used to manage the membership of Internet Protocol multicast groups. ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. ... The Open Shortest Path First (OSPF) protocol is a hierarchical interior gateway protocol (IGP) for routing in Internet Protocol, using a link-state in the individual areas that make up the hierarchy. ... In the field of computer networking, the IETF Signaling Transport (SIGTRAN) working group defined the Stream Control Transmission Protocol (SCTP) as a transport layer protocol in 2000. ... This is a list of IP protocol numbers that defines the number used in the protocol field of IPv4 packets. ...

Fragmentation and reassembly

Main article: IP fragmentation

To make IPv4 more tolerant of different networks the concept of fragmentation was added so that, if necessary, a device could break up the data into smaller pieces. This is necessary when the maximum transmission unit (MTU) is smaller than the packet size. The Internet Protocol allows IP fragmentation so that datagrams can be fragmented into pieces small enough to pass over a link with a smaller MTU than the original datagram size. ... In computer storage, there are three related uses of the term fragmentation: external fragmentation, internal fragmentation, and data fragmentation, all related to storage. ... In computer networking, the term Maximum Transmission Unit (MTU) refers to the size (in bytes) of the largest datagram that a given layer of a communications protocol can pass onwards. ...

For example, the maximum size of an IP packet is 65,535 bytes while the typical MTU for Ethernet is 1,500 bytes. Since the IP header consumes 20 bytes (without options) of the 1,500 bytes leaving 1,480 bytes of IP data per Ethernet frame (this leads to an MTU for IP of 1,480 bytes). Therefore, a 65,535-byte data payload would require 45 packets (65535/1480 = 44.28). Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ...

The reason fragmentation was chosen to occur at the IP layer is that IP is the first layer that connects hosts instead of machines. If fragmentation were performed on higher layers (TCP, UDP, etc.) then this would make fragmentation/reassembly redundantly implemented (once per protocol); if fragmentation were performed on a lower layer (Ethernet, ATM, etc.) then this would require fragmentation/reassembly to be performed on each hop (could be quite costly) and redundantly implemented (once per link layer protocol). Therefore, the IP layer is the most efficient one for fragmentation.

Fragmentation

When a device receives an IP packet it examines the destination address and determines the outgoing interface to use. This interface has an associated MTU that dictates the maximum data size for its payload. If the MTU is smaller than the data size then the device must fragment the data.

The device then segments the data into segments where each segment is less-than-or-equal-to the MTU less the IP header size (20 bytes minimum; 60 bytes maximum). Each segment is then put into its own IP packet with the following changes:

• The total length field will be adjusted to the segment size
• The more fragments (MF) flag is set for all segments except the last one, that would be set to 0
• The fragment offset field is set accordingly based on the offset of the segment in the original data payload. This is measured in units of eight-byte blocks.

For example, for an IP header of length 20 bytes and an Ethernet MTU of 1,500 bytes the fragment offsets would be: 0, (1480/8) = 185, (2960/8) = 370, (4440/8) = 555, (5920/8) = 740, etc.

By some chance if a packet changes link layer protocols or the MTU reduces then these fragments would be fragmented again.

For example, if a 4,500-byte data payload is inserted into an IP packet with no options (thus total length is 4,520 bytes) and is transmitted over a link with an MTU of 2,500 bytes then it will be broken up into two fragments:

Now, let's say the MTU drops to 1,500 bytes. Each fragment will individually be split up into two more fragments each:

Indeed, the amount of data has been preserved — 1480 + 1000 + 1480 + 540 = 4500 — and the last fragment offset plus data — 3960 + 540 = 4500 — is also the total length.

Note that fragments 3 & 4 were derived from the original fragment 2. When a device must fragment the last fragment then it must set the flag for all but the last fragment it creates (fragment 4 in this case). Last fragment would be set to 0 value.

Reassembly

When a receiver detects an IP packet where either of the following is true:

• "more fragments" flag set
• "fragment offset" field is non-zero

then the receiver knows the packet is a fragment. The receiver then stores the data with the identification field, fragment offset, and the more fragments flag. When the receiver receives a fragment with the more fragments flag set to 0 then it knows the length of the original data payload since the fragment offset plus the data length is equivalent to the original data payload size.

Using the example above, when the receiver receives fragment 4 the fragment offset (495 or 3960 bytes) and the data length (540 bytes) added together yield 4500 — the original data length.

Once it has all the fragments then it can reassemble the data in proper order (by using the fragment offsets) and pass it up the stack for further processing.

See also

• Classful network
• Classless Inter-Domain Routing
• Internet Assigned Numbers Authority
• IPv6 and IPv5
• List of assigned /8 IP address blocks
• List of IP protocol numbers
• Regional Internet Registry

Classful networking is the name given to the first round of changes to the structure of the IP address in IPv4. ... Warning! This Article contains disinformation. ... The Internet Assigned Numbers Authority (IANA) is the entity that oversees global IP address allocation, DNS root zone management, and other Internet protocol assignments. ... Internet Protocol version 6 (IPv6) is a network layer for packet-switched internetworks. ... Version 5 of IP was assigned to an experimental protocol called ST2 (Internet Stream Protocol, version 2), which is described in RFC 1819. ... As of January 2006, some /8 (formerly Class A) large blocks of IP addresses assigned to single organizations or related groups of organizations, either by the Internet Corporation for Assigned Names and Numbers (ICANN), through the Internet Assigned Numbers Authority[1] or a regional Internet registry, include: Note that this... Taken from: http://www. ... A Regional Internet Registry (RIR) is an organisation overseeing the allocation and registration of Internet number resources within a particular region of the world. ...

References

1. ^ ICANN Recovers Large Block of Internet Address Space
2. ^ Huston, Geoff. IPv4 Address Report, daily generated. Retrieved on 2007-09-30.
3. ^ Hain, Tony. IPv4 Address Pool, quarterly generated. Retrieved on 2007-07-01.

Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 273rd day of the year (274th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 182nd day of the year (183rd in leap years) in the Gregorian calendar. ...

External links

• RFC 791 — Internet Protocol
• http://www.iana.org — Internet Assigned Numbers Authority (IANA)
• http://www.networksorcery.com/enp/protocol/ip.htm — IP Header Breakdown, including specific options
• RFC 3344 — IPv4 Mobility

Address exhaustion

• RIPE report on address consumption as of October 2003
• Official current state of IPv4 /8 allocations, as maintained by IANA
• Dynamically generated graphs of IPv4 address consumption with predictions of exhaustion dates — Geoff Huston
• IP addressing in China and the myth of address shortage