Classless Inter-Domain Routing
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CIDR
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Classless Inter-Domain Routing (CIDR, pengucapan: /saɪ.dr/ atau /si.dr/) adalah metode untuk mengalokasikan alamat IP dan routing paket Internet Protocol. Internet Engineering Task Force diperkenalkan CIDR pada tahun 1993 untuk menggantikan arsitektur menangani sebelumnya desain jaringan classful di Internet. Tujuannya adalah untuk memperlambat pertumbuhan tabel routing pada router di Internet, dan untuk membantu memperlambat kelelahan cepat alamat IPv4. [1] [2]
Alamat IP yang digambarkan sebagai terdiri dari dua kelompok bit di alamat: bit yang paling signifikan adalah alamat jaringan (network prefix atau atau blok jaringan), yang mengidentifikasi seluruh jaringan atau subnet, dan bentuk-bentuk set paling signifikan host identifier, yang menentukan interface tertentu dari sebuah host pada jaringan itu. Divisi ini digunakan sebagai dasar routing lalu lintas antara jaringan IP dan untuk kebijakan alokasi alamat. Desain jaringan classful untuk IPv4 berukuran alamat jaringan sebagai satu atau lebih kelompok 8-bit, sehingga blok alamat Kelas A, B, atau C. CIDR mengalokasikan ruang alamat ke penyedia layanan Internet dan pengguna akhir pada setiap batas alamat bit, bukan pada segmen 8-bit. Dalam IPv6, bagaimanapun, identifier antarmuka memiliki ukuran tetap 64 bit dengan konvensi, dan subnet yang lebih kecil tidak pernah dialokasikan kepada pengguna akhir.
Notasi CIDR adalah sintaks untuk menentukan alamat IP dan routing yang terkait awalan mereka. Itu menambahkan karakter slash ke alamat dan jumlah desimal bit terkemuka routing prefix, misalnya, 192.168.2.0/24 untuk IPv4, dan 2001: db8 :: / 32 untuk IPv6.
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[hide]Background[edit]
During the first decade of the Internet after the invention of the Domain Name System (DNS) it became apparent that the devised system based on the classful network scheme of allocating the IP address space and the routing of IP packets was not scalable.[3]
To alleviate the shortcomings, the Internet Engineering Task Force published in 1993 a new set of standards, RFC 1518 and RFC 1519, to define a new concept of allocation of IP address blocks and new methods of routing IPv4 packets. A new version of the specification was published as RFC 4632 in 2006.[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 of Internet Protocol Version 4, 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 individual or node address. Thus, the smallest allocation and routing block contained only 256 addresses—too small for most enterprises, and the next larger block contained 65536 addresses—too large to be used efficiently by even large organizations. This led to inefficiencies in address use as well as routing because the large number of allocated small (class-C) networks with individual route announcements, being geographically dispersed with little opportunity for route aggregation, created heavy demand on routing equipment.
As the initial TCP/IP network grew to become the Internet during the 1980s, the need for more flexible addressing schemes became increasingly apparent. This led to the successive development of subnetting and CIDR. The network class distinctions were removed, and the new system was described as being classless, with respect to the old system, which became known as classful.
Classless Inter-Domain Routing is based on variable-length subnet masking (VLSM), which allows a network to be divided into variously sized subnets, providing the opportunity to size a network more appropriately for local needs. Variable-length subnet masks are mentioned in RFC 950.[5] Accordingly, techniques for grouping addresses for common operations were based on the concept of cluster addressing, first proposed by Carl-Herbert Rokitansky.[6][7]
CIDR encompasses several concepts. It is based on the VLSM technique with effective qualities of specifying arbitrary-length prefixes. CIDR introduced a new method of representation for IP addresses, now commonly known as CIDR notation, in which an address or routing prefix is written with a suffix indicating the number of bits of the prefix, such as 192.168.2.0/24. CIDR introduced an administrative process of allocating address blocks to organizations based on their actual and short-term projected needs. The aggregation of multiple contiguous prefixes resulted in supernets in the larger Internet, which whenever possible are advertised as aggregates, thus reducing the number of entries in the global routing table.
CIDR notation[edit]
CIDR notation is a compact representation of an IP address and its associated routing prefix. The notation is constructed from an IP address, a slash ('/') character, and a decimal number. The number is the count of leading 1 bits in the routing mask, traditionally called the network mask. The IP address is expressed according to the standards of IPv4 or IPv6.
The address may denote a single, distinct interface address or the beginning address of an entire network. The maximum size of the network is given by the number of addresses that are possible with the remaining, least-significant bits below the prefix. The aggregation of these bits is often called the host identifier.
For example:
- 192.168.100.14/24 represents the IPv4 address 192.168.100.14 and its associated routing prefix 192.168.100.0, or equivalently, its subnet mask 255.255.255.0, which has 24 leading 1-bits.
- the IPv4 block 192.168.100.0/22 represents the 1024 IPv4 addresses from 192.168.100.0 to 192.168.103.255.
- the IPv6 block 2001:db8::/48 represents the block of IPv6 addresses from 2001:db8:0:0:0:0:0:0 to 2001:db8:0:ffff:ffff:ffff:ffff:ffff.
- ::1/128 represents the IPv6 loopback address. Its prefix size is 128, the size of the address itself.
Before the implementation of CIDR, IPv4 networks were represented by the starting address and the subnet mask, both written in dot-decimal notation notation. Thus, 192.168.100.0/24 was often written as 192.168.100.0/255.255.255.0.
The number of addresses of a subnet may be calculated as 2address size - prefix size, in which the address size is 128 for IPv6 and 32 for IPv4. For example, in IPv4, the prefix size /29 gives: 232-29 = 23 = 8 addresses.
Subnet masks[edit]
A subnet mask is a bitmask that encodes the prefix length in quad-dotted notation: 32 bits, starting with a number of 1 bits equal to the prefix length, ending with 0 bits, and encoded in four-part dotted-decimal format. A subnet mask encodes the same information as a prefix length, but predates the advent of CIDR. However, in CIDR notation, the prefix bits are always contiguous, whereas subnet masks may specify non-contiguous bits. However, this has no practical advantage for increasing efficiency.
CIDR blocks[edit]
CIDR pada prinsipnya bitwise, standar berbasis awalan untuk representasi alamat IP dan sifat routing. Ini memfasilitasi routing dengan memungkinkan blok alamat yang dikelompokkan ke dalam entri tabel routing tunggal. Kelompok-kelompok ini, yang biasa disebut CIDR blok, berbagi urutan awal bit dalam representasi biner dari alamat IP mereka. IPv4 CIDR blok diidentifikasi menggunakan sintaks mirip dengan alamat IPv4: alamat dotted-desimal, diikuti oleh garis miring, maka angka dari 0 sampai 32, yaitu, abcd / n. Bagian desimal bertitik adalah alamat IPv4. Nomor berikut slash adalah panjang awalan, jumlah bit bersama awal, menghitung dari bit yang paling signifikan dari alamat. Ketika menekankan hanya ukuran jaringan, porsi alamat notasi biasanya dihilangkan. Dengan demikian, / 20 blok blok CIDR dengan tidak ditentukan 20-bit prefix.
Sebuah alamat IP adalah bagian dari sebuah blok CIDR, dan dikatakan untuk mencocokkan awalan CIDR jika bit n awal alamat dan awalan CIDR adalah sama. Panjang alamat IPv4 adalah 32 bit, sebuah CIDR awalan n-bit daun 32-bit n tak tertandingi, yang berarti bahwa 232-n IPv4 alamat sesuai yang diberikan n-bit CIDR awalan. Prefiks CIDR pendek cocok lebih alamat, sementara awalan lagi sesuai lebih sedikit. Alamat dapat mencocokkan beberapa CIDR prefiks dengan panjang yang berbeda.
CIDR juga digunakan untuk alamat IPv6 dan semantik sintaks identik. Panjang prefiks dapat berkisar dari 0 sampai 128, karena jumlah yang lebih besar dari bit di alamat. Namun, dengan konvensi subnet pada jaringan lapisan siaran MAC selalu memiliki pengidentifikasi tuan rumah 64-bit. Prefiks lebih besar jarang digunakan bahkan pada point-to-point.
Penugasan blok CIDR [sunting]
Internet Assigned Numbers Authority (IANA) masalah untuk pendaftar Internet regional (RIR) besar, pendek-awalan blok CIDR. Sebagai contoh, 62.0.0.0/8, dengan lebih dari enam belas juta alamat, dikelola oleh RIPE NCC, yang RIR Eropa. RIR, masing-masing bertanggung jawab untuk, besar, wilayah geografis tunggal, seperti Eropa atau Amerika Utara, membagi blok ini dan mengalokasikan subnet untuk pendaftar Internet lokal (LIR). Pengelompokan yang sama dapat diulang beberapa kali di tingkat bawah delegasi. Jaringan end-user menerima subnet berukuran sesuai dengan ukuran jaringan mereka dan diproyeksikan kebutuhan jangka pendek. Jaringan dilayani oleh ISP tunggal didorong oleh rekomendasi IETF untuk mendapatkan ruang alamat IP langsung dari ISP mereka. Jaringan dilayani oleh beberapa ISP, di sisi lain, dapat memperoleh ruang alamat penyedia-independen langsung dari RIR yang sesuai.
IPv4 CIDR blocks[edit]
| IP/CIDR | Δ to last IP addr | Mask | Count of addresses | Relative size to other block sizes | Restrictions on a/b/c/d (0..255 unless noted) |
|---|---|---|---|---|---|
| a.b.c.d/32 | +0.0.0.0 | 255.255.255.255 | 1 | 1/256 C | |
| a.b.c.d/31 | +0.0.0.1 | 255.255.255.254 | 2 | 1/128 C | d = 0 ... (2n) ... 254 |
| a.b.c.d/30 | +0.0.0.3 | 255.255.255.252 | 4 | 1/64 C | d = 0 ... (4n) ... 252 |
| a.b.c.d/29 | +0.0.0.7 | 255.255.255.248 | 8 | 1/32 C | d = 0 ... (8n) ... 248 |
| a.b.c.d/28 | +0.0.0.15 | 255.255.255.240 | 16 | 1/16 C | d = 0 ... (16n) ... 240 |
| a.b.c.d/27 | +0.0.0.31 | 255.255.255.224 | 32 | ⅛ C | d = 0 ... (32n) ... 224 |
| a.b.c.d/26 | +0.0.0.63 | 255.255.255.192 | 64 | ¼ C | d = 0, 64, 128, 192 |
| a.b.c.d/25 | +0.0.0.127 | 255.255.255.128 | 128 | ½ C | d = 0, 128 |
| a.b.c.0/24 | +0.0.0.255 | 255.255.255.000 | 256 | 1 C | |
| a.b.c.0/23 | +0.0.1.255 | 255.255.254.000 | 512 | 2 C | c = 0 ... (2n) ... 254 |
| a.b.c.0/22 | +0.0.3.255 | 255.255.252.000 | 1,024 | 4 C | c = 0 ... (4n) ... 252 |
| a.b.c.0/21 | +0.0.7.255 | 255.255.248.000 | 2,048 | 8 C | c = 0 ... (8n) ... 248 |
| a.b.c.0/20 | +0.0.15.255 | 255.255.240.000 | 4,096 | 16 C | c = 0 ... (16n) ... 240 |
| a.b.c.0/19 | +0.0.31.255 | 255.255.224.000 | 8,192 | 32 C | c = 0 ... (32n) ... 224 |
| a.b.c.0/18 | +0.0.63.255 | 255.255.192.000 | 16,384 | 64 C | c = 0, 64, 128, 192 |
| a.b.c.0/17 | +0.0.127.255 | 255.255.128.000 | 32,768 | 128 C | c = 0, 128 |
| a.b.0.0/16 | +0.0.255.255 | 255.255.000.000 | 65,536 | 256 C = 1 B | |
| a.b.0.0/15 | +0.1.255.255 | 255.254.000.000 | 131,072 | 2 B | b = 0 ... (2n) ... 254 |
| a.b.0.0/14 | +0.3.255.255 | 255.252.000.000 | 262,144 | 4 B | b = 0 ... (4n) ... 252 |
| a.b.0.0/13 | +0.7.255.255 | 255.248.000.000 | 524,288 | 8 B | b = 0 ... (8n) ... 248 |
| a.b.0.0/12 | +0.15.255.255 | 255.240.000.000 | 1,048,576 | 16 B | b = 0 ... (16n) ... 240 |
| a.b.0.0/11 | +0.31.255.255 | 255.224.000.000 | 2,097,152 | 32 B | b = 0 ... (32n) ... 224 |
| a.b.0.0/10 | +0.63.255.255 | 255.192.000.000 | 4,194,304 | 64 B | b = 0, 64, 128, 192 |
| a.b.0.0/9 | +0.127.255.255 | 255.128.000.000 | 8,388,608 | 128 B | b = 0, 128 |
| a.0.0.0/8 | +0.255.255.255 | 255.000.000.000 | 16,777,216 | 256 B = 1 A | |
| a.0.0.0/7 | +1.255.255.255 | 254.000.000.000 | 33,554,432 | 2 A | a = 0 ... (2n) ... 254 |
| a.0.0.0/6 | +3.255.255.255 | 252.000.000.000 | 67,108,864 | 4 A | a = 0 ... (4n) ... 252 |
| a.0.0.0/5 | +7.255.255.255 | 248.000.000.000 | 134,217,728 | 8 A | a = 0 ... (8n) ... 248 |
| a.0.0.0/4 | +15.255.255.255 | 240.000.000.000 | 268,435,456 | 16 A | a = 0 ... (16n) ... 240 |
| a.0.0.0/3 | +31.255.255.255 | 224.000.000.000 | 536,870,912 | 32 A | a = 0 ... (32n) ... 224 |
| a.0.0.0/2 | +63.255.255.255 | 192.000.000.000 | 1,073,741,824 | 64 A | a = 0, 64, 128, 192 |
| a.0.0.0/1 | +127.255.255.255 | 128.000.000.000 | 2,147,483,648 | 128 A | a = 0, 128 |
| 0.0.0.0/0 | +255.255.255.255 | 000.000.000.000 | 4,294,967,296 | 256 A |
Dalam subnet diarahkan lebih besar dari / 31 atau / 32, jumlah alamat host yang tersedia biasanya dikurangi dengan dua, yaitu alamat terbesar, yang dicadangkan sebagai alamat broadcast, dan alamat terkecil, yang mengidentifikasi jaringan itu sendiri. [8] [9]
IPv6 CIDR blok [sunting]
Ukuran alamat besar digunakan di IPv6 diizinkan pelaksanaan seluruh dunia summarization rute dijamin kolam alamat yang cukup di setiap situs. Ukuran subnet standar untuk jaringan IPv6 adalah / 64 blok, yang diperlukan untuk pengoperasian alamat stateless autoconfiguration. [10] Pada awalnya, IETF direkomendasikan dalam RFC 3177 sebagai praktek terbaik yang semua situs akhir menerima alokasi / 48 alamat , [11] Namun, kritik dan reevaluasi kebutuhan dan praktek yang sebenarnya telah menyebabkan rekomendasi alokasi yang lebih fleksibel inRFC 6177 [12] menunjukkan alokasi secara signifikan lebih kecil untuk beberapa situs, seperti / 56 blok untuk jaringan rumah.
Awalan agregasi [sunting]
Artikel utama: Supernetwork
CIDR memberikan kemungkinan halus routing yang prefix agregasi. Misalnya, enam belas bersebelahan / 24 jaringan dapat dikumpulkan dan diiklankan ke jaringan yang lebih besar sebagai single / 20 rute, jika pertama 20 bit alamat jaringan mereka cocok. Dua selaras bersebelahan / 20 blok dapat dikumpulkan ke / 19, dan sebagainya. Hal ini menyebabkan pengurangan jumlah rute yang harus diiklankan.
Lihat juga [sunting]
Protokol internet
Referensi subnetting IPv4
Referensi subnetting IPv6
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