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IP address

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Title: IP address  
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Subject: NetBIOS, Network address translation, Computer network, Dynamic DNS, Google Public DNS
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IP address

s which seldom changes. The addresses are usually assigned with DHCP. Since the modems are usually powered on for extended periods of time, the address leases are usually set to long periods and simply renewed. If a modem is turned off and powered up again before the next expiration of the address lease, it will most likely receive the same IP address.

Address autoconfiguration

RFC 3330 defines an address block, 169.254.0.0/16, for the special use in link-local addressing for IPv4 networks. In IPv6, every interface, whether using static or dynamic address assignments, also receives a local-link address automatically in the block fe80::/10.

These addresses are only valid on the link, such as a local network segment or point-to-point connection, that a host is connected to. These addresses are not routable and like private addresses cannot be the source or destination of packets traversing the Internet.

When the link-local IPv4 address block was reserved, no standards existed for mechanisms of address autoconfiguration. Filling the void, Microsoft created an implementation that is called Automatic Private IP Addressing (APIPA). APIPA has been deployed on millions of machines and has, thus, become a de facto standard in the industry. Many years later, the IETF defined a formal standard for this functionality, RFC 3927, entitled Dynamic Configuration of IPv4 Link-Local Addresses.

Uses of static addressing

Some infrastructure situations have to use static addressing, such as when finding the Domain Name System (DNS) host that will translate domain names to IP addresses. Static addresses are also convenient, but not absolutely necessary, to locate servers inside an enterprise. An address obtained from a DNS server comes with a time to live, or caching time, after which it should be looked up to confirm that it has not changed. Even static IP addresses do change as a result of network administration (RFC 2072).

IP addressing

There are four forms of IP addressing, each with its own unique properties.

  • Unicast: The most common concept of an IP address is in unicast addressing, available in both IPv4 and IPv6. It normally refers to a single sender or a single receiver, and can be used for both sending and receiving. Usually, a unicast address is associated with a single device or host, but it is not a one-to-one correspondence. Some individual PCs have several distinct unicast addresses, each for its own distinct purpose. Sending the same data to multiple unicast addresses requires the sender to send all the data many times over, once for each recipient.
  • Broadcast: In IPv4 it is possible to send data to all possible destinations ("all-hosts broadcast"), which permits the sender to send the data only once, and all receivers receive a copy of it. In the IPv4 protocol, the address 255.255.255.255 is used for local broadcast. In addition, a directed (limited) broadcast can be made by combining the network prefix with a host suffix composed entirely of binary 1s. For example, the destination address used for a directed broadcast to devices on the 192.0.2.0/24 network is 192.0.2.255. IPv6 does not implement broadcast addressing and replaces it with multicast to the specially-defined all-nodes multicast address.
  • Multicast: A multicast address is associated with a group of interested receivers. In IPv4, addresses 224.0.0.0 through 239.255.255.255 (the former Class D addresses) are designated as multicast addresses.[11] IPv6 uses the address block with the prefix ff00::/8 for multicast applications. In either case, the sender sends a single datagram from its unicast address to the multicast group address and the intermediary routers take care of making copies and sending them to all receivers that have joined the corresponding multicast group.
  • Anycast: Like broadcast and multicast, anycast is a one-to-many routing topology. However, the data stream is not transmitted to all receivers, just the one which the router decides is logically closest in the network. Anycast address is an inherent feature of only IPv6. In IPv4, anycast addressing implementations typically operate using the shortest-path metric of BGP routing and do not take into account congestion or other attributes of the path. Anycast methods are useful for global load balancing and are commonly used in distributed DNS systems.

Public addresses

A public IP address, in common parlance, is synonymous with a globally routable unicast IP address.

Both IPv4 and IPv6 define address ranges that are reserved for private networks and link-local addressing. The term public IP address often used excludes these types of addresses.

Modifications to IP addressing

IP blocking and firewalls

Firewalls perform Internet Protocol blocking to protect networks from unauthorized access. They are common on today's Internet. They control access to networks based on the IP address of a client computer. Whether using a blacklist or a whitelist, the IP address that is blocked is the perceived IP address of the client, meaning that if the client is using a proxy server or network address translation, blocking one IP address may block many individual computers.

IP address translation

Multiple client devices can appear to share IP addresses: either because they are part of a shared hosting web server environment or because an IPv4 network address translator (NAT) or proxy server acts as an intermediary agent on behalf of its customers, in which case the real originating IP addresses might be hidden from the server receiving a request. A common practice is to have a NAT hide a large number of IP addresses in a private network. Only the "outside" interface(s) of the NAT need to have Internet-routable addresses.[12]

Most commonly, the NAT device maps TCP or UDP port numbers on the side of the larger, public network to individual private addresses on the masqueraded network.

In small home networks, NAT functions are usually implemented in a residential gateway device, typically one marketed as a "router". In this scenario, the computers connected to the router would have private IP addresses and the router would have a public address to communicate on the Internet. This type of router allows several computers to share one public IP address.

Diagnostic tools

Computer operating systems provide various diagnostic tools to examine their network interface and address configuration. Windows provides the command-line interface tools ipconfig and netsh and users of Unix-like systems can use ifconfig, netstat, route, lanstat, fstat, or iproute2 utilities to accomplish the task.

See also

References

  1. ^ a b c RFC 760, DOD Standard Internet Protocol (January 1980)
  2. ^ a b RFC 791, Internet Protocol – DARPA Internet Program Protocol Specification (September 1981)
  3. ^ a b RFC 1883, Internet Protocol, Version 6 (IPv6) Specification, S. Deering, R. Hinden (December 1995)
  4. ^ a b RFC 2460, Internet Protocol, Version 6 (IPv6) Specification, S. Deering, R. Hinden, The Internet Society (December 1998)
  5. ^ Smith, Lucie; Lipner, Ian (3 February 2011). "Free Pool of IPv4 Address Space Depleted".  
  6. ^ ICANN,nanog mailing list. "Five /8s allocated to RIRs – no unallocated IPv4 unicast /8s remain". 
  7. ^ Asia-Pacific Network Information Centre (15 April 2011). "APNIC IPv4 Address Pool Reaches Final /8". Retrieved 15 April 2011. 
  8. ^ RFC 4193 section 3.2.1
  9. ^ RFC 3513
  10. ^ RFC 3879
  11. ^ RFC 5771
  12. ^

External links

  • IP at DMOZ
  • "Understanding IP Addressing: Everything You Ever Wanted To Know". Archived from the original on 21 August 2010. 
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