IP address
From Wikipedia, the free encyclopedia
An
Internet Protocol address (
IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a
computer network that uses the
Internet Protocol for communication.
[1] An IP address serves two principal functions: host or network interface
identification and location
addressing. 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 designers of the Internet Protocol defined an IP address as a
32-bit number
[1] and this system, known as
Internet Protocol Version 4 (IPv4), is still in use today. However, due to the enormous growth of the
Internet and the predicted
depletion of available addresses, a new version of IP (
IPv6), using 128 bits for the address, was developed in 1995.
[3] IPv6 was standardized as
RFC 2460 in 1998,
[4] and its
deployment has been ongoing since the mid-2000s.
IP addresses are
binary numbers, but they are usually stored in text files and displayed in
human-readable notations, such as 172.16.254.1 (for IPv4), and 2001:db8:0:1234:0:567:8:1 (for IPv6).
The
Internet Assigned Numbers Authority (IANA) manages the IP address space allocations globally and delegates five
regional Internet registries (RIRs) to allocate IP address blocks to
local Internet registries (
Internet service providers) and other entities.
IP versions
Two versions of the Internet Protocol (IP) are in use: IP Version 4
and IP Version 6. Each version defines an IP address differently.
Because of its prevalence, the generic term
IP address typically still refers to the addresses defined by
IPv4. The gap in version sequence between IPv4 and IPv6 resulted from the assignment of number 5 to the experimental
Internet Stream Protocol in 1979, which however was never referred to as IPv5.
IPv4 addresses
In IPv4 an address consists of 32
bits which limits the
address space to
4294967296 (2
32) possible unique addresses. IPv4 reserves some addresses for special purposes such as
private networks (~18 million addresses) or
multicast addresses (~270 million addresses).
IPv4 addresses are canonically represented in
dot-decimal notation,
which consists of four decimal numbers, each ranging from 0 to 255,
separated by dots, e.g., 172.16.254.1. Each part represents a group of 8
bits (
octet) of the address. In some cases of technical writing, IPv4 addresses may be presented in various
hexadecimal,
octal, or
binary representations.
IPv4 subnetting
In the early stages of development of the Internet Protocol,
[1]
network administrators interpreted an IP address in two parts: network
number portion and host number portion. The highest order octet (most
significant eight bits) in an address was designated as the
network number and the remaining bits were called the
rest field or
host identifier and were used for host numbering within a network.
This early method soon proved inadequate as additional networks
developed that were independent of the existing networks already
designated by a network number. In 1981, the Internet addressing
specification was revised with the introduction of
classful network architecture.
[2]
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.
Historical classful network architecture
| Class |
Leading
bits |
Size of network
number bit field |
Size of rest
bit field |
Number
of networks |
Addresses
per network |
Start address |
End address |
| A |
0 |
8 |
24 |
128 (27) |
16,777,216 (224) |
0.0.0.0 |
127.255.255.255 |
| B |
10 |
16 |
16 |
16,384 (214) |
65,536 (216) |
128.0.0.0 |
191.255.255.255 |
| C |
110 |
24 |
8 |
2,097,152 (221) |
256 (28) |
192.0.0.0 |
223.255.255.255 |
Classful network design served its purpose in the startup stage of the Internet, but it lacked
scalability in the face of the rapid expansion of the network in the 1990s. The class system of the address space was replaced with
Classless Inter-Domain Routing
(CIDR) in 1993. CIDR is based on variable-length subnet masking (VLSM)
to allow allocation and routing based on arbitrary-length prefixes.
Today, remnants of classful network concepts function only in a
limited scope as the default configuration parameters of some network
software and hardware components (e.g. netmask), and in the technical
jargon used in network administrators' discussions.
IPv4 private addresses
Early network design, when global end-to-end connectivity was
envisioned for communications with all Internet hosts, intended that IP
addresses be uniquely assigned to a particular computer or device.
However, it was found that this was not always necessary as
private networks developed and public address space needed to be conserved.
Computers not connected to the Internet, such as factory machines
that communicate only with each other via TCP/IP, need not have globally
unique IP addresses. Three ranges of IPv4 addresses for private
networks were reserved in
RFC 1918. These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry.
Today, when needed, such private networks typically connect to the Internet through
network address translation (NAT).
IANA-reserved private IPv4 network ranges
|
Start |
End |
No. of addresses |
| 24-bit block (/8 prefix, 1 × A) |
10.0.0.0 |
10.255.255.255 |
16777216 |
| 20-bit block (/12 prefix, 16 × B) |
172.16.0.0 |
172.31.255.255 |
1048576 |
| 16-bit block (/16 prefix, 256 × C) |
192.168.0.0 |
192.168.255.255 |
65536 |
Any user may use any of the reserved blocks. Typically, a network administrator will divide a block into
subnets; for example, many
home routers automatically use a default address range of 192.168.0.0 through 192.168.0.255 (192.168.0.0/24).
IPv4 address exhaustion
IPv4 address exhaustion is the decreasing supply of unallocated
Internet Protocol Version 4 (IPv4) addresses available at the
Internet Assigned Numbers Authority (IANA) and the
regional Internet registries (RIRs) for assignment to end users and
local Internet registries, such as
Internet service providers. IANA's primary
address pool was exhausted on 3 February 2011, when the last 5 blocks were allocated to the 5 RIRs.
[5][6] APNIC
was the first RIR to exhaust its regional pool on 15 April 2011, except
for a small amount of address space reserved for the transition to
IPv6, intended to be allocated in a restricted process.
[7]
IPv6 addresses
Main article:
IPv6 address
Decomposition of an IPv6 address from
hexadecimal representation to its binary value.
The rapid exhaustion of IPv4 address space, despite conservation techniques, prompted the
Internet Engineering Task Force
(IETF) to explore new technologies to expand the addressing capability
in the Internet. The permanent solution was deemed to be a redesign of
the Internet Protocol itself. This next generation of the Internet
Protocol, intended to replace IPv4 on the Internet, was eventually named
Internet Protocol Version 6 (IPv6) in 1995.
[3][4] The address size was increased from 32 to 128
bits or 16
octets.
This, even with a generous assignment of network blocks, is deemed
sufficient for the foreseeable future. Mathematically, the new address
space provides the potential for a maximum of 2
128, or about
3.403×1038 addresses.
The primary intent of the new design is not to provide just a
sufficient quantity of addresses, but rather to allow an efficient
aggregation of subnetwork routing prefixes at routing nodes. As a
result, routing table sizes are smaller, and the smallest possible
individual allocation is a subnet for 2
64 hosts, which is the
square of the size of the entire IPv4 Internet. At these levels, actual
address utilization rates will be small on any IPv6 network segment.
The new design also provides the opportunity to separate the addressing
infrastructure of a network segment, that is the local administration of
the segment's available space, from the addressing prefix used to route
external traffic for a network. IPv6 has facilities that automatically
change the routing prefix of entire networks, should the global
connectivity or the routing policy change, without requiring internal
redesign or manual renumbering.
The large number of IPv6 addresses allows large blocks to be assigned
for specific purposes and, where appropriate, to be aggregated for
efficient routing. With a large address space, there is not the need to
have complex address conservation methods as used in CIDR.
Many modern desktop and enterprise server operating systems include
native support for the IPv6 protocol, but it is not yet widely deployed
in other devices, such as home networking routers,
voice over IP (VoIP) and multimedia equipment, and network peripherals.
IPv6 private addresses
Just as IPv4 reserves addresses for private or internal networks,
blocks of addresses are set aside in IPv6 for private addresses. In
IPv6, these are referred to as
unique local addresses (ULA).
RFC 4193
sets aside the routing prefix fc00::/7 for this block which is divided
into two /8 blocks with different implied policies. The addresses
include a 40-bit pseudorandom number that minimizes the risk of address
collisions if sites merge or packets are misrouted.
[8]
Early designs used a different block for this purpose (fec0::), dubbed site-local addresses.
[9] However, the definition of what constituted
sites
remained unclear and the poorly defined addressing policy created
ambiguities for routing. This address range specification was abandoned
and must not be used in new systems.
[10]
Addresses starting with fe80:, called
link-local
addresses, are assigned to interfaces for communication on the link
only. The addresses are automatically generated by the operating system
for each network interface. This provides instant and automatic network
connectivity for any IPv6 host and means that if several hosts connect
to a common hub or switch, they have a communication path via their
link-local IPv6 address. This feature is used in the lower layers of
IPv6 network administration (e.g.
Neighbor Discovery Protocol).
None of the private address prefixes may be routed on the public Internet.
IP subnetworks
IP networks may be divided into
subnetworks in both
IPv4 and
IPv6. For this purpose, an IP address is logically recognized as consisting of two parts: the
network prefix and the
host identifier, or
interface identifier (IPv6). The
subnet mask or the CIDR prefix determines how the IP address is divided into network and host parts.
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.
IP address assignment
Internet Protocol addresses are assigned to a host either anew at the
time of booting, or permanently by fixed configuration of its hardware
or software. Persistent configuration is also known as using a
static IP address. In contrast, in situations when the computer's IP address is assigned newly each time, this is known as using a
dynamic IP address.
Methods
Static IP addresses are manually assigned to a computer by an
administrator. The exact procedure varies according to platform. This
contrasts with dynamic IP addresses, which are assigned either by the
computer interface or host software itself, as in
Zeroconf, or assigned by a server using
Dynamic Host Configuration Protocol
(DHCP). Even though IP addresses assigned using DHCP may stay the same
for long periods of time, they can generally change. In some cases, a
network administrator may implement dynamically assigned static IP
addresses. In this case, a DHCP server is used, but it is specifically
configured to always assign the same IP address to a particular
computer. This allows static IP addresses to be configured centrally,
without having to specifically configure each computer on the network in
a manual procedure.
In the absence or failure of static or stateful (DHCP) address
configurations, an operating system may assign an IP address to a
network interface using state-less auto-configuration methods, such as
Zeroconf.
Uses of dynamic address assignment
IP addresses are most frequently assigned dynamically on LANs and broadband networks by the
Dynamic Host Configuration Protocol
(DHCP). They are used because it avoids the administrative burden of
assigning specific static addresses to each device on a network. It also
allows many devices to share limited address space on a network if only
some of them will be online at a particular time. In most current
desktop operating systems, dynamic IP configuration is enabled by
default so that a user does not need to manually enter any settings to
connect to a network with a DHCP server. DHCP is not the only technology
used to assign IP addresses dynamically. Dialup and some broadband
networks use dynamic address features of the
Point-to-Point Protocol.
Sticky dynamic IP address
A
sticky dynamic IP address is an informal term used by cable
and DSL Internet access subscribers to describe a dynamically assigned
IP address 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). Due to Microsoft's market power, 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.
[citation needed]
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.
Konsep Dasar Subneting
Konsep
subnetting merupakan teknik yang umum digunakan di jaringan lokal.
Subnetting merupakan proses memecah satu network dalam satu kelas IP
Address menjadi beberapa subnet. Dengan subnetting jumlah host yang
semula banyak dalam satu network akan dipecah menjadi lebih sedikit,
dan dengan subnetting dapat dilakukan pemisahan network agar tidak
saling terkoneksi satu sama lain. Subnetting juga dapat digunakan untuk
menentukan batas network ID dalam suatu subnet, serta menentukan
jumlah host maksimal dalam satu jaringan, teknik yang dipakai
menggunakan subnet mask yang spesifik. Dengan menggunakan teknik
subnetting, sebuah LAN dapat dipecah jadi dua LAN. Dua LAN menjadi
empat, empat LAN jadi delapan dan seterusnya.
Subnetmask default
Kelas A : 255.0.0.0
Kelas B : 255.255.0.0
Kelas C : 255.255.255.0
Pembagian Kelas
Kelas A : 0-126 .0.0.0
Kelas B :128-191.0.0.0
Kelas C :197-223.0.0.0
Kelas D :224-239.0.0.0 (MultiCast)
Kelas E :239-255.0.0.0 (Pengembangan)
Contoh: 1 blok IP
Address klas C: 192.168.0/24 , jumlah komputer max 1 LAN = 254 (ranges
IP address 192.168.0.1 s/d 192.168.0.254, netmask 255.255.255.0),
dipecah menjadi 2 subnet dengan netmask 255.255.255.128, dan kemudian
dapat dipecah jadi 4 subnet dengan netmask 255.255.255.192, dan
seterusnya, seperti:
Lan 1 192.168.0.1 s/d 192.168.0.126 192.168.0.129 s/d 192.168.0.254 Lan 2
Lan 1 192.168.0.1 s/d 192.168.0.62 192.168.0.129 s/d 192.168.0.190 Lan 3
LAN 2 192.168.0.65 s/d 192.168.0.126 192.168.0.193 s/d 192.168.0.254 Lan 4
Seperti yang
telah dijelaskan pada bab sebelumnya, bahwa selain menggunakan metode
classfull untuk pembagian IP address, kita juga dapat menggunakan
metode classless addressing (pengalamatan tanpa klas), menggunakan
notasi penulisan singkat dengan prefix. Metode ini merupakan metode
pengalamatan IPv4 tingkat lanjut, muncul karena ada kekhawatiran
persediaan Ipv4 berkelas tidak akan mencukupi kebutuhan, sehingga
diciptakan metode lain untuk memperbanyak persediaan IP.
Contoh Kasus (Class C):
Untuk CIDR (Classless Inter-Domain Routing) /24 (kolom pertama, baris terakhir), dengan bilangan biner 256. Maka subnet mask-nya 255.255.255.0. Dengan 0
terakhir diambil dari tabel baris ke 3 kolom pertama. Sehingga host
yang mungkin adalah berjumlah 254 Host (Bilangan biner 256-2=254, 2
adalah jumlah host yang dipinjam untuk digunakan sebagai IP Subnet (IP
Awal) dan IP Broadcast (IP Akhir)). Contoh lainnya adalah: CIDR /26
(kolom ke tiga, baris terakhir), kita mulai dari Bilangan Biner 64.
Disitulah subnetnya. Kita punya 4 buah jaringan, dimana masing-masing
memiliki 62 host/komputer (64-2 =126). Jadi pada intinya, dalam sebuah
kasus Subnetting, ada 4 hal yang biasanya perlu diketahui:
- Jumlah Subnet. Berada pada baris ke empat. Misal:192.168.1.0/26, akan mempunyai 4 buah subnet.
- Jumlah Host/Komputer per Subnet.
Berada pada baris ke lima. Untuk IP 192.168.1.0/26, jumlah host per
subnet adalah 62 hosts (64-2=62). Contoh: Range IP Host salah satu
subnet adalah 192.168.1.1-192.168.1.62. Dimana 192.168.1.0 digunakan untuk Subnet pertama, dan 192.168.1.63 digunakan sebagai IP Broadcast.
- Blok Subnet. Berada pada baris pertama. Sehingga untuk CIDR /26, blok-blok subnet nya adalah: 192.168.1.0, 192.168.1.64, 192.168.1.128, dan 192.168.1.192 (Kelipatan 64 bit sejumlah 4 subnet).
- IP Host dan IP Broadcast yang valid.
Seperti yang telah dijelaskan pada nomor 2, Jumlah subnet akan
berpengaruh terhadap jumlah IP Address yang dapat digunakan. Pada
tiap-tiap subnet, IP Awal dikenal dengan IP Subnet, sedangkan IP Akhir
dikenal sebagai IP Broadcast. Sedangkan IP sisanya, adalah IP yang
dapat digunakan untuk host.
Contoh-contoh
di atas merupakan contoh yang diambil dari IP Address Kelas C. Adapun
untuk Subnet dari kelas lain dapat dilihat seperti gambar berikut:
PENGHITUNGAN SUBNETTING
Penulisan IP
address umumnya adalah dengan 192.168.1.2. Namun adakalanya ditulis
dengan 192.168.1.2/24. Artinya bahwa IP address 192.168.1.2 dengan
subnet mask 255.255.255.0. Di mana /24 diambil dari penghitungan bahwa
24 bit subnet mask diselubung dengan binari 1. Atau dengan kata lain,
subnet masknya adalah: 11111111.11111111.11111111.00000000
(255.255.255.0). Konsep ini yang disebut dengan CIDR (Classless
Inter-Domain Routing) yang diperkenalkan pertama kali tahun 1992 oleh
IEFT.
KEUNTUNGAN SUBNETTING
- Menyederhanakan administrasi
- Perubahan stuktur jaringan tidak tampak dari luar
- Keamanan jaringan lebih baik
- Berkurangnya
lalu lintas jaringan. Untuk mengkomunikasikan beberapa subnet dalam
sebuah jaringan, maka kita harus menggunakan sebuah router. Dengan
adanya router, maka semua lalu lintas hanya akan berada didalam
jaringan tersebut, kecuali jika paket tersebut ditujukan kepada
jaringan yang lainnya. Sehingga Kerja jaringan menjadi optimal
- Pengelolaan
yang sederhana. Akan lebih mudah bagi kita untuk mengelola sebuah
jaringan kecil-kecil yang saling terisolasi jika dibandingkan dengan
mengelola sebuah jaringan tunggal yang sangat besar.
- Membantu
pengembangan jaringan dengan jarak geografis yang jauh. Karena jalur
dalam WAN yang lebih lambat dan mahal, maka sebuah jaringan yang
mencakup jarak yang jauh akan menciptakan masalah masalah diatas.
Sehingga menghubungkan banyak jaringan kecil akan menjadi lebih efisien
