Internet Protocol version 4
Protocol stack | |
Abbreviation | IPv4 |
---|---|
Purpose | Internetworking protocol |
Developer(s) | DARPA |
Introduction | 1981 |
Influenced | IPv6 |
OSI layer | Network layer |
RFC(s) | 791 |
Internet protocol suite |
---|
Application layer |
Transport layer |
Internet layer |
Link layer |
Internet Protocol version 4 (IPv4) is the fourth version of the
IPv4 uses a
History
Internet Protocol version 4 is described in
Purpose
The Internet Protocol is the protocol that defines and enables
IPv4 is a
Addressing
IPv4 uses 32-bit addresses which limits the address space to 4294967296 (232) addresses.
IPv4 reserves special address blocks for private networks (~18 million addresses) and multicast addresses (~270 million addresses).
Address representations
IPv4 addresses may be represented in any notation expressing a 32-bit integer value. They are most often written in dot-decimal notation, which consists of four octets of the address expressed individually in decimal numbers and separated by periods.
For example, the quad-dotted IP address in the illustration (172.16.254.1) represents the 32-bit decimal number 2886794753, which in hexadecimal format is 0xAC10FE01.
Other address representations were in common use when classful networking was practiced. For example, the loopback address 127.0.0.1 was commonly written as 127.1, given that it belongs to a class-A network with eight bits for the network mask and 24 bits for the host number. When fewer than four numbers were specified in the address in dotted notation, the last value was treated as an integer of as many bytes as are required to fill out the address to four octets. Thus, the address 127.65530 is equivalent to 127.0.255.250.
Allocation
In the original design of IPv4, an IP address was divided into two parts: the network identifier was the most significant octet of the address, and the host identifier was the rest of the address. The latter was also called the rest field. This structure permitted a maximum of 256 network identifiers, which was quickly found to be inadequate.
To overcome this limit, the most-significant address octet was redefined in 1981 to create network classes, in a system which later became known as classful networking. The revised system defined five classes. Classes A, B, and C had different bit lengths for network identification. The rest of the address was used as previously to identify a host within a network. Because of the different sizes of fields in different classes, each network class had a different capacity for addressing hosts. In addition to the three classes for addressing hosts, Class D was defined for multicast addressing and Class E was reserved for future applications.
Dividing existing classful networks into subnets began in 1985 with the publication of
Special-use addresses
The Internet Engineering Task Force (IETF) and IANA have restricted from general use various reserved IP addresses for special purposes.[4] Notably these addresses are used for multicast traffic and to provide addressing space for unrestricted uses on private networks.
Special address blocks Address block Address range Number of addresses Scope Description 0.0.0.0/8 0.0.0.0–0.255.255.255 16777216 Software Current (local, "this") network[4] 10.0.0.0/8 10.0.0.0–10.255.255.255 16777216 Private network Used for local communications within a private network[7] 100.64.0.0/10 100.64.0.0–100.127.255.255 4194304 Private network Shared address space[8] for communications between a service provider and its subscribers when using a carrier-grade NAT 127.0.0.0/8 127.0.0.0–127.255.255.255 16777216 Host Used for loopback addresses to the local host[4]169.254.0.0/16 169.254.0.0–169.254.255.255 65536 Subnet Used for DHCPserver172.16.0.0/12 172.16.0.0–172.31.255.255 1048576 Private network Used for local communications within a private network[7] 192.0.0.0/24 192.0.0.0–192.0.0.255 256 Private network IETF Protocol Assignments, DS-Lite (/29)[4]192.0.2.0/24 192.0.2.0–192.0.2.255 256 Documentation Assigned as TEST-NET-1, documentation and examples[10] 192.88.99.0/24 192.88.99.0–192.88.99.255 256 Internet Reserved.[11] Formerly used for IPv6 to IPv4 relay[12] (included IPv6 address block 2002::/16). 192.168.0.0/16 192.168.0.0–192.168.255.255 65536 Private network Used for local communications within a private network[7] 198.18.0.0/15 198.18.0.0–198.19.255.255 131072 Private network Used for benchmark testing of inter-network communications between two separate subnets[13] 198.51.100.0/24 198.51.100.0–198.51.100.255 256 Documentation Assigned as TEST-NET-2, documentation and examples[10] 203.0.113.0/24 203.0.113.0–203.0.113.255 256 Documentation Assigned as TEST-NET-3, documentation and examples[10] 224.0.0.0/4 224.0.0.0–239.255.255.255 268435456 Internet In use for multicast[14] (former Class D network) 233.252.0.0/24 233.252.0.0–233.252.0.255 256 Documentation Assigned as MCAST-TEST-NET, documentation and examples (Note that this is part of the above multicast space.)[14][15] 240.0.0.0/4 240.0.0.0–255.255.255.254 268435455 Internet Reserved for future use[16] (former Class E network) 255.255.255.255/32 255.255.255.255 1 Subnet Reserved for the "limited broadcast" destination address[4]
Private networks
Of the approximately four billion addresses defined in IPv4, about 18 million addresses in three ranges are reserved for use in private networks. Packets addresses in these ranges are not routable in the public Internet; they are ignored by all public routers. Therefore, private hosts cannot directly communicate with public networks, but require network address translation at a routing gateway for this purpose.
Reserved private IPv4 network ranges[7] Name CIDR block Address range Number of addresses Classful description 24-bit block 10.0.0.0/8 10.0.0.0 – 10.255.255.255 16777216 Single Class A 20-bit block 172.16.0.0/12 172.16.0.0 – 172.31.255.255 1048576 Contiguous range of 16 Class B blocks 16-bit block 192.168.0.0/16 192.168.0.0 – 192.168.255.255 65536 Contiguous range of 256 Class C blocks
Since two private networks, e.g., two branch offices, cannot directly interoperate via the public Internet, the two networks must be bridged across the Internet via a virtual private network (VPN) or an IP tunnel, which encapsulates packets, including their headers containing the private addresses, in a protocol layer during transmission across the public network. Additionally, encapsulated packets may be encrypted for transmission across public networks to secure the data.
Link-local addressing
RFC 3927 defines the special address block 169.254.0.0/16 for link-local addressing. These addresses are only valid on the link (such as a local network segment or point-to-point connection) directly connected to a host that uses them. These addresses are not routable. Like private addresses, these addresses cannot be the source or destination of packets traversing the internet. These addresses are primarily used for address autoconfiguration (
When the address block was reserved, no standards existed for address autoconfiguration.
Loopback
The class A network 127.0.0.0 (classless network 127.0.0.0/8) is reserved for loopback. IP packets whose source addresses belong to this network should never appear outside a host. Packets received on a non-loopback interface with a loopback source or destination address must be dropped.
First and last subnet addresses
The first address in a subnet is used to identify the subnet itself. In this address all host bits are 0. To avoid ambiguity in representation, this address is reserved.[17] The last address has all host bits set to 1. It is used as a local broadcast address for sending messages to all devices on the subnet simultaneously. For networks of size /24 or larger, the broadcast address always ends in 255.
For example, in the subnet 192.168.5.0/24 (subnet mask 255.255.255.0) the identifier 192.168.5.0 is used to refer to the entire subnet. The broadcast address of the network is 192.168.5.255.
Type | Binary form | Dot-decimal notation |
---|---|---|
Network space | 11000000.10101000.00000101.00000000
|
192.168.5.0 |
Broadcast address | 11000000.10101000.00000101.11111111
|
192.168.5.255 |
In red, is shown the host part of the IP address; the other part is the network prefix. The host gets inverted (logical NOT), but the network prefix remains intact. |
However, this does not mean that every address ending in 0 or 255 cannot be used as a host address. For example, in the /16 subnet 192.168.0.0/255.255.0.0, which is equivalent to the address range 192.168.0.0–192.168.255.255, the broadcast address is 192.168.255.255. One can use the following addresses for hosts, even though they end with 255: 192.168.1.255, 192.168.2.255, etc. Also, 192.168.0.0 is the network identifier and must not be assigned to an interface.[18]: 31 The addresses 192.168.1.0, 192.168.2.0, etc., may be assigned, despite ending with 0.
In the past, conflict between network addresses and broadcast addresses arose because some software used non-standard broadcast addresses with zeros instead of ones.[18]: 66
In networks smaller than /24, broadcast addresses do not necessarily end with 255. For example, a CIDR subnet 203.0.113.16/28 has the broadcast address 203.0.113.31.
Type | Binary form | Dot-decimal notation |
---|---|---|
Network space | 11001011.00000000.01110001.00010000
|
203.0.113.16 |
Broadcast address | 11001011.00000000.01110001.00011111
|
203.0.113.31 |
In red, is shown the host part of the IP address; the other part is the network prefix. The host gets inverted (logical NOT), but the network prefix remains intact. |
As a special case, a /31 network has capacity for just two hosts. These networks are typically used for point-to-point connections. There is no network identifier or broadcast address for these networks.[19]
Address resolution
Hosts on the Internet are usually known by names, e.g., www.example.com, not primarily by their IP address, which is used for routing and network interface identification. The use of domain names requires translating, called resolving, them to addresses and vice versa. This is analogous to looking up a phone number in a phone book using the recipient's name.
The translation between addresses and domain names is performed by the Domain Name System (DNS), a hierarchical, distributed naming system that allows for the subdelegation of namespaces to other DNS servers.
Unnumbered interface
A unnumbered point-to-point (PtP) link, also called a transit link, is a link that does not have an IP network or subnet number associated with it, but still has an IP address. First introduced in 1993,[20][21][22][23] Phil Karn from Qualcomm is credited as the original designer.
The purpose of a transit link is to route datagrams. They are used to free IP addresses from a scarce IP address space or to reduce the management of assigning IP and configuration of interfaces. Previously, every link needed to dedicate a /31 or /30 subnet using 2 or 4 IP addresses per point-to-point link. When a link is unnumbered, a router-id is used, a single IP address borrowed from a defined (normally a loopback) interface. The same router-id can be used on multiple interfaces.
One of the disadvantages of unnumbered interfaces is that it is harder to do remote testing and management.
Address space exhaustion
In the 1980s, it became apparent that the pool of available IPv4 addresses was depleting at a rate that was not initially anticipated in the original design of the network.
- Classless Inter-Domain Routing (CIDR), for smaller ISP allocations
- Unnumbered interfaces removed the need for addresses on transit links.
- Network address translation (NAT) removed the need for the end-to-end principle.
By the mid-1990s, NAT was used pervasively in network access provider systems, along with strict usage-based allocation policies at the regional and local Internet registries.
The primary address pool of the Internet, maintained by IANA, was exhausted on 3 February 2011, when the last five blocks were allocated to the five
The long-term solution to address exhaustion was the 1998 specification of a new version of the Internet Protocol, IPv6.[28] It provides a vastly increased address space, but also allows improved route aggregation across the Internet, and offers large subnetwork allocations of a minimum of 264 host addresses to end users. However, IPv4 is not directly interoperable with IPv6, so that IPv4-only hosts cannot directly communicate with IPv6-only hosts. With the phase-out of the 6bone experimental network starting in 2004, permanent formal deployment of IPv6 commenced in 2006.[29] Completion of IPv6 deployment is expected to take considerable time,[30] so that intermediate transition technologies are necessary to permit hosts to participate in the Internet using both versions of the protocol.
Packet structure
An IP
Header
The IPv4 packet header consists of 14 fields, of which 13 are required. The 14th field is optional and aptly named: options. The fields in the header are packed with the most significant byte first (
Offsets | Octet | 0 | 1 | 2 | 3 | ||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Octet | Bit | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 |
0 | 0 | Version | IHL | DSCP | ECN | Total length | |||||||||||||||||||||||||||
4 | 32 | Identification | Flags | Fragment offset | |||||||||||||||||||||||||||||
8 | 64 | Time to Live | Protocol | Header checksum | |||||||||||||||||||||||||||||
12 | 96 | Source address | |||||||||||||||||||||||||||||||
16 | 128 | Destination address | |||||||||||||||||||||||||||||||
20 | 160 | Options (if IHL > 5) | |||||||||||||||||||||||||||||||
⋮ | ⋮ | ||||||||||||||||||||||||||||||||
56 | 448 |
- Version
- The first header field in an IP packetis the four-bit version field. For IPv4, this is always equal to 4.
- Internet Header Length (IHL)
- The IPv4 header is variable in size due to the optional 14th field (options). The IHL field contains the size of the IPv4 header; it has 4 bits that specify the number of 32-bit words in the header. The minimum value for this field is 5,[32] which indicates a length of 5 × 32 bits = 160 bits = 20 bytes. As a 4-bit field, the maximum value is 15; this means that the maximum size of the IPv4 header is 15 × 32 bits = 480 bits = 60 bytes.
- Differentiated Services Code Point(DSCP)
- Originally defined as the type of service (ToS), this field specifies differentiated services (DiffServ).[33] Real-time data streaming makes use of the DSCP field. An example is Voice over IP (VoIP), which is used for interactive voice services.
- Explicit Congestion Notification (ECN)
- This field allows end-to-end notification of network congestion without dropping packets.[34] ECN is an optional feature available when both endpoints support it and effective when also supported by the underlying network.
- Total Length
- This 16-bit field defines the entire packet size in bytes, including header and data. The minimum size is 20 bytes (header without data) and the maximum is 65,535 bytes. All hosts are required to be able to reassemble datagrams of size up to 576 bytes, but most modern hosts handle much larger packets. Links may impose further restrictions on the packet size, in which case datagrams must be fragmented. Fragmentation in IPv4 is performed in either the sending host or in routers. Reassembly is performed at the receiving host.
- Identification
- This field is an identification field and is primarily used for uniquely identifying the group of fragments of a single IP datagram. Some experimental work has suggested using the ID field for other purposes, such as for adding packet-tracing information to help trace datagrams with spoofed source addresses,[35] but any such use is now prohibited.[36]
- Flags
- A three-bit field follows and is used to control or identify fragments. They are (in order, from most significant to least significant):
- bit 0: Reserved; must be zero.[a]
- bit 1: Don't Fragment (DF)
- bit 2: More Fragments (MF)
- If the DF flag is set, and fragmentation is required to route the packet, then the packet is dropped. This can be used when sending packets to a host that does not have resources to perform reassembly of fragments. It can also be used for path MTU discovery, either automatically by the host IP software, or manually using diagnostic tools such as ping or traceroute.
- For unfragmented packets, the MF flag is cleared. For fragmented packets, all fragments except the last have the MF flag set. The last fragment has a non-zero Fragment Offset field, differentiating it from an unfragmented packet.
- Fragment offset
- This field specifies the offset of a particular fragment relative to the beginning of the original unfragmented IP datagram. The fragmentation offset value for the first fragment is always 0. The field is 13 bits wide, so that the offset can be from 0 to 8191 (from (20 – 1) to (213 – 1)). Fragments are specified in units of 8 bytes, which is why fragment length must be a multiple of 8.[37] Therefore, the 13-bit field allows a maximum offset of (213 – 1) × 8 = 65,528 bytes, with the header length included (65,528 + 20 = 65,548 bytes), supporting fragmentation of packets exceeding the maximum IP length of 65,535 bytes.
- Time to live (TTL)
- An eight-bit ICMP time exceededmessage to the sender.
- The program traceroute sends messages with adjusted TTL values and uses these ICMP time exceeded messages to identify the routers traversed by packets from the source to the destination.
- Protocol
- This field defines the protocol used in the data portion of the IP datagram. IANA maintains a list of IP protocol numbers.[38]
- Header checksum
- The 16-bit IPv4 header checksum field is used for error checking of the header. When a packet arrives at a router or its destination, the network device calculates the checksum of the header including the checksum field. A value of 0xFFFF is expected. If a different result is obtained, the device discards the packet. Errors in the data portion of the packet are handled separately by the encapsulated protocol. Both UDP and TCPhave separate checksums that apply to their data.
- When a packet arrives at a router, the router decreases the TTL field in the header. Consequently, the router must calculate a new header checksum.
- The checksum field is the 16-bit ones' complement of the ones' complement sum of all 16-bit words in the header. For purposes of computing the checksum, the value of the checksum field is zero.
- Source address
- This 32-bit field is the IPv4 address of the sender of the packet. It may be changed in transit by network address translation(NAT).
- Destination address
- This 32-bit field is the IPv4 addressof the receiver of the packet. It may be affected by NAT.
- Options
- The some options may be considered as dangerous by some routers and be blocked.[39]The value in the IHL field must include sufficient extra 32-bit words to hold all options and any padding needed to ensure that the header contains an integral number of 32-bit words. If IHL is greater than 5 (i.e., it is from 6 to 15) it means that the options field is present and must be considered. The list of options may be terminated with the option EOOL (End of Options List, 0x00); this is only necessary if the end of the options would not otherwise coincide with the end of the header.
- Since most of the IP options include specifications how many or which intermediate devices the packet should pass, the IP options are not used for communication over the Internet and IP packets including some of the IP options must dropped as per IPv4 security assessment RFC6274, since they can expose the network topology or network details.
- The possible options that can be put in the header are as follows:
Field Size (bits) Description Copied 1 Set to 1 if the options need to be copied into all fragments of a fragmented packet. Option Class 2 A general options category. 0 is for control options, and 2 is for debugging and measurement. 1 and 3 are reserved. Option Number 5 Specifies an option. Option Length 8 Indicates the size of the entire option (including this field). This field may not exist for simple options. Option Data Variable Option-specific data. This field may not exist for simple options.
- The table below shows the defined options for IPv4. The Option Type column is derived from the Copied, Option Class, and Option Number bits as defined above.[40]
Option Type (decimal/hexadecimal) Option Name Description 0/0x00 EOOL End of Option List 1/0x01 NOP No Operation 2/0x02 SEC Security (defunct) 7/0x07 RR Record Route 10/0x0A ZSU Experimental Measurement 11/0x0B MTUP MTU Probe 12/0x0C MTUR MTU Reply 15/0x0F ENCODE ENCODE 25/0x19 QS Quick-Start 30/0x1E EXP RFC3692-style Experiment 68/0x44 TS Time Stamp 82/0x52 TR Traceroute 94/0x5E EXP RFC3692-style Experiment 130/0x82 SEC Security (RIPSO) 131/0x83 LSR Loose Source Route 133/0x85 E-SEC Extended Security (RIPSO) 134/0x86 CIPSO Commercial IP Security Option 136/0x88 SID Stream ID 137/0x89 SSR Strict Source Route 142/0x8E VISA Experimental Access Control 144/0x90 IMITD IMI Traffic Descriptor 145/0x91 EIP Extended Internet Protocol 147/0x93 ADDEXT Address Extension 148/0x94 RTRALT Router Alert 149/0x95 SDB Selective Directed Broadcast 151/0x97 DPS Dynamic Packet State 152/0x98 UMP Upstream Multicast Packet 158/0x9E EXP RFC3692-style Experiment 205/0xCD FINN Experimental Flow Control 222/0xDE EXP RFC3692-style Experiment
Data
The packet payload is not included in the checksum. Its contents are interpreted based on the value of the Protocol header field.
List of IP protocol numbers contains a complete list of payload protocol types. Some of the common payload protocols include:
Protocol Number | Protocol Name | Abbreviation |
---|---|---|
1 | Internet Control Message Protocol | ICMP |
2 | Internet Group Management Protocol | IGMP |
6 | Transmission Control Protocol | TCP |
17 | User Datagram Protocol | UDP |
41 | IPv6 encapsulation | ENCAP |
89 | Open Shortest Path First | OSPF |
132 | Stream Control Transmission Protocol | SCTP |
Fragmentation and reassembly
The Internet Protocol enables traffic between networks. The design accommodates networks of diverse physical nature; it is independent of the underlying transmission technology used in the link layer. Networks with different hardware usually vary not only in transmission speed, but also in the
In contrast, IPv6, the next generation of the Internet Protocol, does not allow routers to perform fragmentation; hosts must perform Path MTU Discovery before sending datagrams.
Fragmentation
When a router receives a packet, it examines the destination address and determines the outgoing interface to use and that interface's MTU. If the packet size is bigger than the MTU, and the Do not Fragment (DF) bit in the packet's header is set to 0, then the router may fragment the packet.
The router divides the packet into fragments. The maximum size of each fragment is the outgoing MTU minus the IP header size (20 bytes minimum; 60 bytes maximum). The router puts each fragment into its own packet, each fragment packet having the following changes:
- The total length field is the fragment size.
- The more fragments (MF) flag is set for all fragments except the last one, which is set to 0.
- The fragment offset field is set, based on the offset of the fragment in the original data payload. This is measured in units of 8-byte blocks.
- The header checksum field is recomputed.
For example, for an MTU of 1,500 bytes and a header size of 20 bytes, the fragment offsets would be multiples of (0, 185, 370, 555, 740, etc.).
It is possible that a packet is fragmented at one router, and that the fragments are further fragmented at another router. For example, a packet of 4,520 bytes, including a 20 bytes IP header is fragmented to two packets on a link with an MTU of 2,500 bytes:
Fragment | Size (bytes) |
Header size (bytes) |
Data size (bytes) |
Flag More fragments |
Fragment offset (8-byte blocks) |
---|---|---|---|---|---|
1 | 2,500 | 20 | 2,480 | 1 | 0 |
2 | 2,040 | 20 | 2,020 | 0 | 310 |
The total data size is preserved: 2,480 bytes + 2,020 bytes = 4,500 bytes. The offsets are and .
When forwarded to a link with an MTU of 1,500 bytes, each fragment is fragmented into two fragments:
Fragment | Size (bytes) |
Header size (bytes) |
Data size (bytes) |
Flag More fragments |
Fragment offset (8-byte blocks) |
---|---|---|---|---|---|
1 | 1,500 | 20 | 1,480 | 1 | 0 |
2 | 1,020 | 20 | 1,000 | 1 | 185 |
3 | 1,500 | 20 | 1,480 | 1 | 310 |
4 | 560 | 20 | 540 | 0 | 495 |
Again, the data size is preserved: 1,480 + 1,000 = 2,480, and 1,480 + 540 = 2,020.
Also in this case, the More Fragments bit remains 1 for all the fragments that came with 1 in them and for the last fragment that arrives, it works as usual, that is the MF bit is set to 0 only in the last one. And of course, the Identification field continues to have the same value in all re-fragmented fragments. This way, even if fragments are re-fragmented, the receiver knows they have initially all started from the same packet.
The last offset and last data size are used to calculate the total data size: .
Reassembly
A receiver knows that a packet is a fragment, if at least one of the following conditions is true:
- The flag more fragments is set, which is true for all fragments except the last.
- The field fragment offset is nonzero, which is true for all fragments except the first.
The receiver identifies matching fragments using the source and destination addresses, the protocol ID, and the identification field. The receiver reassembles the data from fragments with the same ID using both the fragment offset and the more fragments flag. When the receiver receives the last fragment, which has the more fragments flag set to 0, it can calculate the size of the original data payload, by multiplying the last fragment's offset by eight and adding the last fragment's data size. In the given example, this calculation was bytes. When the receiver has all fragments, they can be reassembled in the correct sequence according to the offsets to form the original datagram.
Assistive protocols
IP addresses are not tied in any permanent manner to networking hardware and, indeed, in modern
See also
Notes
- April Fools' joke, proposed for use in RFC 3514 as the "Evil bit"
- ^ For IEEE 802 networking technologies, including Ethernet, the hardware address is a MAC address.
References
This article was adapted from the following source under a CC BY 4.0 license (2022) :
Michel Bakni; Sandra Hanbo (9 December 2022). "A Survey on Internet Protocol version 4 (IPv4)" (PDF). WikiJournal of Science. {{cite journal}}
: CS1 maint: unflagged free DOI (link
- ^ "BGP Analysis Reports". BGP Reports. Retrieved 2013-01-09.
- ^ "IPv6 – Google". www.google.com. Retrieved 2022-01-28.
- ^ "IANA IPv4 Special-Purpose Address Registry". www.iana.org. Retrieved 2022-01-28.
- ^ .
- ^ "A Brief History of IPv4". IPv4 Market Group. Retrieved 2020-08-19.
- ^ "Understanding IP Addressing: Everything You Ever Wanted To Know" (PDF). 3Com. Archived from the original (PDF) on June 16, 2001.
- ^ .
- .
- . Proposed Standard.
- ^ .
- .
- .
- .
- ^ .
- . Informational.
- .
- .
Special Addresses: In certain contexts, it is useful to have fixed addresses with functional significance rather than as identifiers of specific hosts. When such usage is called for, the address zero is to be interpreted as meaning "this", as in "this network".
- ^ .
- . Proposed Standard.
- ^ Almquist, Philip; Kastenholz, Frank (December 1993). "Towards Requirements for IP Routers". Internet Engineering Task Force.
- .
- .
- ^ "Understanding and Configuring the ip unnumbered Command". Cisco. Retrieved 2021-11-25.
- ^ "World 'running out of Internet addresses'". Archived from the original on 2011-01-25. Retrieved 2011-01-23.
- Number Resource Organization. Retrieved 3 February 2011.
- ^ ICANN,nanog mailing list. "Five /8s allocated to RIRs – no unallocated IPv4 unicast /8s remain".
- ^ Asia-Pacific Network Information Centre (15 April 2011). "APNIC IPv4 Address Pool Reaches Final /8". Archived from the original on 7 August 2011. Retrieved 15 April 2011.
- .
- .
- OCLC 972636788.
- .
- .
- .
- .
- .
- .
- ^ Bhardwaj, Rashmi (2020-06-04). "Fragment Offset - IP With Ease". ipwithease.com. Retrieved 2022-11-21.
- .Obsoletes IENs: 127, 117, 93.
- ^ "Cisco unofficial FAQ". Retrieved 2012-05-10.
- ^ "Internet Protocol Version 4 (IPv4) Parameters".
External links
- Internet Assigned Numbers Authority (IANA)
- IP, Internet Protocol Archived 2011-05-14 at the Wayback Machine — IP Header Breakdown, including specific options
- IP Mobility Support for IPv4. RFC 3344.
- Official current state of IPv4/8 allocations, as maintained by IANA