What is the first part of an IP address?
38404#4
An IP address is interpreted as composed of two parts: a network-identifying prefix followed by a host identifier within that network. In the previous classful network architecture, IP address allocations were based on the bit boundaries of the four octets of an IP address. An address was considered to be the combination of an 8, 16, or 24-bit network prefix along with a 24, 16, or 8-bit host identifier respectively. Thus, the smallest allocation and routing block contained only 256 addresses—too small for most enterprises, and the next larger block contained addresses—too large to be used efficiently even by large organizations. This led to inefficiencies in address use as well as inefficiencies in routing, because it required a large number of allocated class-C networks with individual route announcements, being geographically dispersed with little opportunity for route aggregation.
Classless Inter-Domain Routing
14921#4
An IP address serves two principal functions. It identifies the host, or more specifically its network interface, and it provides the location of the host in the network, and thus the capability of establishing a path to that host. 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."
The header of each IP packet contains the IP address of the sending host, and that of the destination host.
IP address
1323247#6
The first specification of IP tunneling was in RFC 1075, which described DVMRP, the first IP multicast routing protocol. Because multicast used special IPv4 addresses, testing DVMRP required a way to get IP datagrams across portions of the Internet that did not yet recognize multicast addresses. This was solved by IP tunneling. The first approach to IP tunneling used an IP Loose Source Route and Record (LSRR) Option to hide the multicast address from the non-multicast aware routers. A multicast-aware destination router would remove the LSRR option from the packet and restore the multicast IP address to the packet's IP destination field. The other approach in the DVMRP specification was IP in IP, as described above. IP in IP soon became the preferred approach, and was later put to use in the Mbone.
IP tunnel
57836368#5
The first deployment scenario is where the network operator provides a hybrid CPE router to each subscriber but no specialised equipment in the operator's network. There are two possible configurations for IP addresses. A first deployment scenario is to allocate different IP addresses to the wired and wireless interfaces. In this case, the hybrid CPE router needs to load-balance intelligently the packets over the two networks. In particular, it must ensure that all packets belonging to a given TCP connection are sent over the same interface. A second deployment scenario is to allocate the same IP address to both the wired and the wireless networks and configure the routing in these networks to ensure that packets or correctly routed.
Hybrid Access Networks
622150#3
The hosts file contains lines of text consisting of an IP address in the first text field followed by one or more host names. Each field is separated by white space – tabs are often preferred for historical reasons, but spaces are also used. Comment lines may be included; they are indicated by an octothorpe (#) in the first position of such lines. Entirely blank lines in the file are ignored. For example, a typical hosts file may contain the following:
This example only contains entries for the loopback addresses of the system and their host names, a typical default content of the hosts file. The example illustrates that an IP address may have multiple host names ("localhost" and "loopback"), and that a host name may be mapped to both IPv4 and IPv6 IP addresses, as shown on the first and second lines respectively.
Hosts (file)
14539#23
The most prominent component of the Internet model is the Internet Protocol (IP), which provides addressing systems, including IP addresses, for computers on the network. IP enables internetworking and, in essence, establishes the Internet itself. Internet Protocol Version 4 (IPv4) is the initial version used on the first generation of the Internet and is still in dominant use. It was designed to address up to ≈4.3 billion (10) hosts. However, the explosive growth of the Internet has led to IPv4 address exhaustion, which entered its final stage in 2011, when the global address allocation pool was exhausted. A new protocol version, IPv6, was developed in the mid-1990s, which provides vastly larger addressing capabilities and more efficient routing of Internet traffic. IPv6 is currently in growing deployment around the world, since Internet address registries (RIRs) began to urge all resource managers to plan rapid adoption and conversion.
Internet
14921#9
The term "subnet mask" is only used within IPv4. Both IP versions however use the 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 and , respectively. The CIDR notation for the same IP address and subnet is , because the first 24 bits of the IP address indicate the network and subnet.
IP address
436706#7
No formal specification of this textual IP address representation exists. The first mention of this format in RFC documents was in RFC 780 for the Mail Transfer Protocol published May 1981, in which the IP address was supposed to be enclosed in brackets or represented as a 32bit decimal integer prefixed by a pound sign. A table in RFC 790 ("Assigned Numbers") used the dotted decimal format, zero-padding each number to three digits. RFC 1123 ("Requirements for Internet Hosts – Application and Support") from October 1989 mentions a requirement on host software to accept “IP address in dotted-decimal ("#.#.#.#") form”, although it notes “[t]his last requirement is not intended to specify the complete syntactic form for entering a dotted-decimal host number”. A separate IETF draft to define textual representation of IP addresses expired.
Dot-decimal notation
2527345#16
IPv4 multicast packets are delivered using the Ethernet MAC address range 01:00:5e:00:00:00–01:00:5e:7f:ff:ff (with an OUI owned by the IANA). This range has 23 bits of available address space. The first octet (01) includes the broadcast/multicast bit. The lower 23 bits of the 28-bit multicast IP address are mapped into the 23 bits of available Ethernet address space. This means that there is ambiguity in delivering packets. If two hosts on the same subnet each subscribe to a different multicast group whose address differs only in the first 5 bits, Ethernet packets for both multicast groups will be delivered to both hosts, requiring the network software in the hosts to discard the unrequired packets.
IP multicast
14921#13
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.
IP address
14921#8
IP networks may be divided into subnetworks in both IPv4 and IPv6. For this purpose, an IP address is recognized as consisting of two parts: the "network prefix" in the high-order bits and the remaining bits called the "rest field", "host identifier", or "interface identifier" (IPv6), used for host numbering within a network. The subnet mask or CIDR notation determines how the IP address is divided into network and host parts.
IP address