Instruct: Given a question, retrieve passages that answer the question.
Query: What is the first part of an IP address?
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."[2] The header of each IP packet contains the IP address of the sending host, and that of the destination host.
IP addresses are assigned to a host either dynamically at the time of booting, or permanently by fixed configuration of the host hardware or software. Persistent configuration is also known as using a static IP address. In contrast, when a computer's IP address is assigned newly each time it restarts, this is known as using a dynamic IP address.
However, the Internet was not designed for anonymity: IP addresses serve as virtual mailing addresses, which means that any time any resource on the Internet is accessed, it is accessed from a particular IP address, and the data traffic patterns to and from IP addresses can be intercepted, monitored, and analysed, even if the content of that traffic is encrypted. This address can be mapped to a particular Internet Service Provider (ISP), and this ISP can then provide information about what customer that IP address was leased to. This does not necessarily implicate a specific individual (because other people could be using that customer's connection, especially if the customer is a public resource, such as a library), but it provides regional information and serves as powerful circumstantial evidence.
IP stacks need to correlate Ethernet addresses (MAC address) and IP addresses, using a specific protocol named ARP. When a RTP-MIDI application wants to send a packet to a remote device, it must locate it first on the network, since Ethernet does not understand IP-related concepts, in order to create the transmission path between the routers/switches. This is done automatically by the IP stack by sending first an ARP (Address Recognition Protocol) request. When the destination device recognizes its own IP address in the ARP packet, it sends back an ARP reply with its MAC address. The IP stack can then send the RTP-MIDI packet. The next RTP-MIDI packets do not need the ARP sequence anymore, unless the link becomes inactive for a few minutes, which clears the ARP entry in the sender's routing table.
Additional functionality, such as controlling reservations in DHCP and other data aggregation and reporting capabilities, is also common. Data tracked by an IPAM system may include information such as IP addresses in use, the devices an IP is assigned to at what time, as well as to which user an IP was assigned. This information can also support troubleshooting and abuse investigations. 
A public IP address, in common parlance, is a globally routable unicast IP address, meaning that the address is not an address reserved for use in private networks, such as those reserved by RFC, or the various IPv6 address formats of local scope or site-local scope, for example for link-local addressing. Public IP addresses may be used for communication between hosts on the global Internet.
Masks are used with IP addresses in IP ACLs (Access Control Lists) to specify what should be permitted and denied. To configure IP addresses on interfaces, masks start with 255 and have the large values on the left side: for example, IP address 209.165.202.129 with a 255.255.255.224 mask. Masks for IP ACLs are the reverse: for example, mask 0.0.0.255. This is sometimes called an inverse mask or a wildcard mask. When the value of the mask is broken down into binary (0s and 1s), the results determine which address bits are to be considered in processing the traffic. A 0 indicates that the address bits must be considered (exact match); a 1 in the mask is a "don't care". This table further explains the concept.
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.[1] The subnet mask or CIDR notation determines how the IP address is divided into network and host parts.
Similar to war dialing is a port scan under TCP/IP, which "dials" every TCP port of every IP address to find out what services are available. Unlike wardialing, however, a port scan will generally not disturb a human being when it tries an IP address, regardless of whether there is a computer responding on that address or not. Related to wardriving is warchalking, the practice of drawing chalk symbols in public places to advertise the availability of wireless networks.
Cisco "RAPT" implementation is port address translation (PAT) or NAT overloading, and maps multiple private IP addresses to a single public IP address. Multiple addresses can be mapped to a single address because each private address is tracked by a port number. PAT uses unique source port numbers on the inside global IP address to distinguish between translations. The port number are 16-bit integers. The total number of internal addresses that can be translated to one external address could theoretically be as high as 65,536 per IP address. Realistically, the number of ports that can be assigned a single IP address is around 4000. PAT attempts to preserve the original source port. If this source port is already used, PAT assigns the first available port number starting from the beginning of the appropriate port group 0-511, 512-1023, or 1024-65535. When there are no more ports available and there is more than one external IP address configured, PAT moves to the next IP address to try to allocate the original source port again. This process continues until it runs out of available ports and external IP addresses.
A typical CMTS allows a subscriber's computer to obtain an IP address by forwarding DHCP requests to the relevant servers. This DHCP server returns, for the most part, what looks like a typical response including an assigned IP address for the computer, gateway/router addresses to use, DNS servers, etc.
An important additional feature of codice_1 is to force refreshing of the DHCP IP address of the host computer to request a different IP address. This is done using two commands in sequence. First, codice_6 is executed to force the client to immediately give up its lease by sending the server a DHCP release notification which updates the server's status information and marks the old client's IP address as "available". Then, the command codice_7 is executed to request a new IP address. Where a computer is connected to a cable or DSL modem, it may have to be plugged directly into the modem network port to bypass the router, before using codice_6 and turning off the power for a period of time, to ensure that the old IP address is taken by another computer.
For one-to-many NAT, a VIP address is advertised from the NAT device (often a router), and incoming data packets destined to that VIP address are routed to different actual IP addresses (with address translation). These VIP addresses have several variations and implementation scenarios, including Common Address Redundancy Protocol (CARP) and Proxy ARP. In addition, if there are multiple actual IP addresses, load balancing can be performed as part of NAT.
The important parts of this PAP message are the address value and type. The value is typically a MSISDN and type indicates whether to send to an MSISDN (typical case) or to an IP Address. The TYPE is almost always MSISDN as the Push Initiator (PI) will not typically have the Mobile Station's IP address - which is generally dynamic. In the case of IP Address:
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.
The Internet Protocol is the protocol that defines and enables internetworking at the Internet Layer and thus forms the Internet. It uses a logical addressing system. IP addresses are not tied in any permanent manner to hardware identifications and, indeed, a network interface can have multiple IP addresses. Hosts and routers need additional mechanisms to identify the relationship between device interfaces and IP addresses, in order to properly deliver an IP packet to the destination host on a link. The Address Resolution Protocol (ARP) performs this IP-address-to-hardware-address translation for IPv4. (A hardware address is also called a MAC address.) In addition, the reverse correlation is often necessary. For example, when an IP host is booted or connected to a network it needs to determine its IP address, unless an address is preconfigured by an administrator. Protocols for such inverse correlations exist in the Internet Protocol Suite. Currently used methods are Dynamic Host Configuration Protocol (DHCP), Bootstrap Protocol (BOOTP) and, infrequently, reverse ARP.
Furthermore, if the Domain Name System (DNS) is not properly functioning, it is difficult to access a virtually-hosted website even if the IP address is known. If the user tries to fall back to using the IP address to contact the system, as in http://10.23.45.67/, the web browser will send the IP address as the host name. Since the web server relies on the web browser client telling it what server name (vhost) to use, the server will respond with a default website—often not the site the user expects.
Initially, users are able to choose a range of IP addresses for their VPC. Within this range, users can assign various private and public IPv4 and IPv6 addresses to instances in the VPC in order to communicate with the Internet and other instances of VPCs. These addresses are assigned to specific instances rather than the user's entire VPC account.
Static assignment of Public IP addresses is not possible, instead the address is assigned and unassigned in certain cases, causing the address of an instance to change. When a consistent IP address is needed, a third type of IP Address, Elastic IP addresses, can be used in place of Public IP addresses.
The hosts file is one of several system facilities that assists in addressing network nodes in a computer network. It is a common part of an operating system's Internet Protocol (IP) implementation, and serves the function of translating human-friendly hostnames into numeric protocol addresses, called IP addresses, that identify and locate a host in an IP network.
On a website, an IP address block can prevent a disruptive address from access, though a warning and/or account block may be used first. Dynamic allocation of IP addresses by ISPs can complicate incoming IP address blocking, rendering it difficult to block a specific user without blocking many IP addresses (blocks of IP address ranges), thereby creating collateral damage.
IP address blocking can be used to restrict access to or from a particular geographic area—for example, the syndication of content to a specific region. To achieve this, IP addresses are mapped to the countries they have been assigned to. This has been used for example to target Nigerian IP addresses due to the perception that all business originating from the country is fraudulent, thus making it extremely difficult for legitimate businesses based in the country to interact with their counterparts in the rest of the world. To make purchases abroad, Nigerians must rely on proxy servers to disguise the true origin of an Internet request.
Each router has an identifier, customarily written in the dotted decimal format (e.g., 1.2.3.4) of an IP address. This identifier must be established in every OSPF instance. If not explicitly configured, the highest logical IP address will be duplicated as the router identifier. However, since the router identifier is not an IP address, it does not have to be a part of any routable subnet in the network, and often isn't to avoid confusion.
IP masquerading is a technique that hides an entire IP address space, usually consisting of private IP addresses, behind a single IP address in another, usually public address space. The address that has to be hidden is changed into a single (public) IP address as "new" source address of the outgoing IP packet so it appears as originating not from the hidden host but from the routing device itself. Because of the popularity of this technique to conserve IPv4 address space, the term "NAT" has become virtually synonymous with IP masquerading.
In its simplest implementation, Round-robin DNS works by responding to DNS requests not only with a single potential IP address, but with one out of a list of potential IP addresses corresponding to several servers that host identical services. The order in which IP addresses from the list are returned is the basis for the term "round robin". With each DNS response, the IP address sequence in the list is permuted. Usually, basic IP clients attempt connections with the first address returned from a DNS query, so that on different connection attempts, clients would receive service from different providers, thus distributing the overall load among servers.
Classless Inter-Domain Routing Hostname IP address spoofing IP aliasing IP multicast List of assigned /8 IPv4 address blocks MAC address Regional Internet registry Reverse DNS lookup Virtual IP address WHOIS
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 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.