Classless Inter-Domain Routing (CIDR) Overview
제가 설명능력이 부족한 관계로 웹사이트를 긁었는뎅...영문사이트네요..부분부분 허접해석 달겠습니다..
What Is CIDR? CIDR 이 모냥?
CIDR is a new addressing scheme for the Internet which allows for more efficient allocation of IP addresses than the old Class A, B, and C address scheme.
CIDR 은 A,B,C Class 와 같은 오래된 주소체계보다 더 충분한 IP 주소들을 할당할 수 있는 새로운 주소할당 방법이다.
Why Do We Need CIDR? CIDR 이 왜 필요하징?
With a new network being connected to the Internet every 30 minutes the Internet was faced with two critical problems:
세상이 좋아져서 새로운 네트웍이 빠르게 증가하면서 인터넷은 두가지 큰 문제에 직면하게 된당...(의역 ㅡㅡ;;)
- Running out of IP addresses : IP 주소의 고갈
- Running out of capacity in the global routing tables : 공인 라우팅 테이블에서의 수용력 고갈
There is a maximum number of networks and hosts that can be assigned unique addresses using the Internet's 32-bit long addresses. Traditionally, the Internet assigned "classes" of addresses: Class A, Class B and Class C were the most common. Each address had two parts: one part to identify a unique network and the second part to identify a unique host in that network. Another way the old Class A, B, and C addresses were identified was by looking at the first 8 bits of the address and converting it to its decimal equivalent.
Using the old Class A, B, and C addressing scheme the Internet could support the following: A,B,C Class 주소 체계를 사용하면 인터넷상에서 다음과 같은 네트워크들을 지원하게 됩니다. (Some addresses are reserved for broadcast messages, etc.). Because Internet addresses were generally only assigned in ( 몇몇 주소들은 Broadcast 나 Multicast, VRRP Message 등의 용도로 예약되어있음) 인터넷 주소가 일반적으로 오직 3개의 사이즈 these three sizes, there was a lot of wasted addresses. For example, if you needed 100 addresses you would be assigned the ( A,B,C Class ) 로만 할당되어있기 때문에 주소의 낭비가 많다. 왜냐하면, 만약 당신이 100개의 주소를 필요로 할 경우 가장 작은 smallest address (Class C), but that still meant 154 unused addresses. The overall result was that while the Internet was C Class 의 주소를 사용하게 되겠지만 이 경우 154 개의 주소가 남겨지므로 낭비이당. 위와 같은 현상 때문에 인터넷 상에서 사용하지 running out of unassigned addresses, only 3% of the assigned addresses were actually being used. CIDR was developed to be 않는 주소로 인항 주소의 고갈이 생기게 되었고 오직 3%의 할당된 주소들만이 사용되게 되었다. CIDR 은 더욱 충분한 주소를 효과적으로 a much more efficient method of assigning addresses. 할당하기 위해 개발된 방법이다. Global Routing Tables At Capacity 전체 라우팅 테이블 용량 A related problem was the sheer size of the Internet global routing tables. As the number of networks on the Internet increased, 관련된 문제로 인터넷 전체 라우팅 테이블의 사이즈의 크기가 있다. 인터넷상에서 네트워크의 수가 증가하게 되면서 그 경로의 수도 so did the number of routes. A few years back it was forecasted that the global backbone Internet routers were fast approaching 증가하게 되었다. 몇년 되지 않아서 전세계 인터넷 백본 라우터들은 각 장비가 지원할 수 있는 라우팅 경로의 한계에 도달하게 되었다. their limit on the number of routes they could support. Even using the latest router technology, the maximum theoretical routing table size is approximately 60,000 routing table entries. If 비록 최근의 라우터 기술을 이용할지라도 이론적으로 라우팅 테이블 엔트리의 수는 최대 6만개에 이른다. 만약 nothing was done the global routing tables would have reached capacity by mid-1994 and all Internet growth would be halted. 전체 라우팅 테이블에 대해 아무런 것도 하지 않고 방치하였다면 1994년 중반에 이르러 한계에 이르게 되고 인터넷의 성장은 멈추었을 것이다. Two solutions were developed and adopted by the global Internet community: 두 가지 솔루션이 개발되었고 전세계 인터넷 통신에 채택되었다. Restructuring IP Address Assignments IP 주소할당의 재구성 Classless Inter-Domain Routing (CIDR) is a replacement for the old process of assigning Class A, B and C addresses with a CIDR 은 오래된 A,B,C Class 의 주소 할당 방법을 "Prefix" 를 이용한 방법으로 교체하였습니당...^^ generalized network "prefix". Instead of being limited to network identifiers (or "prefixes") of 8, 16 or 24 bits, CIDR currently uses 네트워크를 구분짓기 위해 8,16,24 bits 로 한정된 "Prefixes" 를 사용하는 대신, CIDR 은 13~27 에 이르 prefixes anywhere from 13 to 27 bits. Thus, blocks of addresses can be assigned to networks as small as 32 hosts or to those 는 다양한 Prefix 를 사용합니당. 이처럼 작게는 32개의 호스트를 갖는 네트워크를 할당하거나 혹은 50,000 개의 호스트를 갖는 네트워크 with over 500,000 hosts. This allows for address assignments that much more closely fit an organization's specific needs. 를 할당 할 수 있습니다. 이와 같은 주소할당 방법은 각 조직이 요구하는 Need ( 필요 Host 수) 에 더욱 근접한 주소할당을 가능하게 합니당. A CIDR address includes the standard 32-bit IP address and also information on how many bits are used for the network prefix. CIDR 주소는 표준 32-bit IP 주소를 포함하며 또한 네트워크 Prefix 에 사용되는 bit 의 정보를 포함하기도 합니다. For example, in the CIDR address 206.13.01.48/25, the "/25" indicates the first 25 bits are used to identify the unique network 예를 들어 206.13.01.48/25 와 같은 CIDR 주소에서 "/25" 는 처음 25 bit 가 네트워크를 구분하기 위한 용도로 사용되고 있다는 것을 leaving the remaining bits to identify the specific host. 나타내며 나머지 bit 가 호스트를 나타낸다는 것을 뜻합니다. Hierarchical Routing Aggregation To Minimize Routing Table Entries 라우팅 테이블 엔트리를 최소화하기 위하여 계층적 라우팅 통합 ( Supernetting 에 대한 계념적 설명입니다.) 해석은 요기까지 The CIDR addressing scheme also enables "route aggregation" in which a single high-level route entry can represent many lower-level routes in the global routing tables. The scheme is similar to the telephone network where the network is setup in a hierarchical structure. A high level, backbone network node only looks at the area code information and then routes the call to the specific backbone node responsible for that area code. The receiving node then looks at the phone number prefix and routes the call to its subtending network node responsible for that prefix and so on. The backbone network nodes only need routing table entries for area codes, each representing huge blocks of individual telephone numbers, not for every unique telephone number. Currently, big blocks of addresses are assigned to the large Internet Service Providers (ISPs) who then re-allocate portions of their address blocks to their customers. For example, Pacific Bell Internet has been assigned a CIDR address block with a prefix of /15 (equivalent to 512 Class C addresses or 131,072 host addresses) and typically assigns its customers CIDR addresses with prefixes ranging from /27 to /19. These customers, who may be smaller ISPs themselves, in turn re-allocate portions of their address block to their users and/or customers. However, in the global routing tables all these different networks and hosts can be represented by the single Pacific Bell Internet route entry. In this way, the growth in the number of routing table entries at each level in the network hierarchy has been significantly reduced. Currently, the global routing tables have approximately 35,000 entries. The Internet is currently a mixture of both "CIDR-ized" addresses and old Class A, B and C addresses. Almost all new routers support CIDR and the Internet authorities strongly encourage all users to implement the CIDR addressing scheme. (We recommend that any new router you purchase should support CIDR). The conversion to the CIDR addressing scheme and route aggregation has two major user impacts: Justifying IP Address Assignments Even with the introduction of CIDR, the Internet is growing so fast that address assignments must continue to be treated as a scarce resource. As such, customers will be required to document, in detail, their projected needs. Users may be required from time to time to document their internal address assignments, particularly when requesting additional addresses. The current Internet guideline is to assign addresses based on an organization's projected three month requirement with additional addresses assigned as needed. Where To Get Address Assignments In the past, you would get a Class A, B or C address assignments directly from the appropriate Internet Registry (i.e., the InterNIC). Under this scenario, you "owned" the address and could take it with you even if you changed Internet Service Providers (ISPs). With the introduction of CIDR address assignments and route aggregation, with a few exceptions, the recommended source for address assignments is your ISP. Under this scenario, you are only "renting" the address and if you change ISPs it is strongly recommended that you get a new address from your new ISP and re-number all of your network devices. While this can be a time-consuming task, it is critical for your address to be aggregated into your ISP's larger address block and routed under their network address. There are still significant global routing table issues and the smaller your network is, the greater your risk of being dropped from the global routing tables. In fact, networks smaller than 8,192 devices will very likely be dropped. Neither the InterNIC nor other ISPs have control over an individual ISP's decisions on how to manage their routing tables. As an option to physically re-numbering each network device, some organizations are using proxy servers to translate old network addresses to their new addresses. Users should be cautioned to carefully consider all the potential impacts before using this type of solution. As mentioned before, there are a few exceptions where an organization would not use an ISP assigned address block.Address Class # Network Bits # Hosts Bits Decimal Address Range Class A 8 bits 24 bits 1-126 Class B 16 bits 16 bits 128-191 Class C 24 bits 8 bits 192-223
How Were These Problems Solved? 어떻게 이런 문제들을 해결했나?
CIDR Block Prefix # Equivalent Class C # of Host Addresses /27 1/8th of a Class C 32 hosts /26 1/4th of a Class C 64 hosts /25 1/2 of a Class C 128 hosts /24 1 Class C 256 hosts /23 2 Class C 512 hosts /22 4 Class C 1,024 hosts /21 8 Class C 2,048 hosts /20
16 Class C
4,096 hosts
/19
32 Class C
8,192 hosts
/18
64 Class C
16,384 hosts
/17
128 Class C
32,768 hosts
/16
256 Class C
65,536 hosts
(= 1 Class B)
/15
512 Class C
131,072 hosts
/14
1,024 Class C
262,144 hosts
/13 2,048 Class C 524,288 hosts User Impacts
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