RFC 1466

Guidelines for Management of IP Address Space

📅 published May 1993, from ietf

RFC 1466 🎀 "Guidelines for Management of IP Address Space" is by E. Gerich from Merit, written for the Network Working Group and dated May 1993 📅 It obsoletes RFC 1366 💅 and its status is info-only: it provides information for the Internet community and does not specify an Internet standard 🧚

Status of This Memo ✨

Okay, the fine print first 📝 This memo is here to give info to the Internet community. It does not specify an Internet standard, and distribution of this memo is unlimited 🦋

Abstract 🌸

The Federal Engineering Planning Group (FEPG) reviewed this on behalf of the Federal Networking Council (FNC). The co-chairs of the Intercontinental Engineering Planning Group (IEPG) and the Reseaux IP Europeens (RIPE) looked at it too 👑 Those groups generally agreed on the recommendations for managing the IP address space, so it's got a whole squad of approval 🫶

1.0 Introduction ✨

The Internet kept growing and going global, so people started thinking hard about how network numbers get allocated and assigned 🌍 RFC 1174, "Identifier Assignment and Connected Status" [1], dated August 1990, recommends that the Internet Registry (IR) stay the main registry for network numbers 👑 The IR may allocate blocks of network numbers and assign those numbers to qualified organizations. If no delegated registration authority has been identified, the IR is the default registry 🧚

Distributing the registration function is desirable, so we need a plan to manage how the network number space gets spread out 🌈 Demand has grown a lot in the last two years, which means allocation must be approached in a more systematic way 💅

This document proposes a plan that moves forward the implementation of RFC 1174 and defines how the network number space gets allocated and assigned. There are three big topics:

Qualifications for Distributed Regional Registries 🌸
Allocation of the Network Number Space by the Internet Registry 🍓
Assignment of the Network Numbers 💜

2.0 Qualifications for Distributed Regional Registries 🌈

So why distribute? The Internet serves a way more diverse global crowd than it did at the start 🌍 Registries in distinct geographic areas can serve their local communities better, especially when it comes to language and local customs 🗣️ Everyone's into the idea, but we need to define how candidate delegated registries get chosen and which geographic areas they come from 🧐

Based on how mature the Internet is in Europe, North America, Central/South America, and the Pacific Rim, it's worth considering delegating registration to an organization in each of those areas 🌎 Until an organization is identified in a region, the IR keeps being the default registry there. The IR remains the root registry and keeps providing registration for every region not covered by a distributed regional registry 👑 As other regions get more active on the Internet, the Internet Assigned Numbers Authority (IANA) and the IR may go looking for candidate registries to serve those areas too 🧚

The regional registry has to be unbiased and widely recognized by network providers and subscribers in its region 🫶 It's also key that there's just one regional registry per geographic region at this level, so sub-allocation of the address space stays efficient and fair ⚖️ To be selected as a distributed regional registry, an organization should meet these criteria:

a) networking authorities within the geographic area give the organization their legitimacy,
b) the organization is well-established and has legitimacy beyond the registry function,
c) the organization commits appropriate resources to provide stable, timely, and reliable service to the geographic region,
d) it is committed to allocating IP numbers according to the guidelines established by the IANA and the IR, and
e) it is committed to coordinating with the IR to establish qualifications and strategies for sub-allocations of the regional allocation.

The distributed regional registry is empowered by the IANA and the IR to provide the network number registration function for a geographic area 💅 Network applicants can still contact the IR directly. Depending on the circumstances, a network subscriber may be referred to the regional registry, but the IR is ready to serve any network subscriber if necessary 🫶

3.0 Allocation of the Network Number Space by the Internet Registry 🦋

The Class A portion of the number space is 50% of the total IP host addresses, Class B is 25%, and Class C is roughly 12% 📊 Here's the current allocation of IP network numbers in Table 1:

                   Total           Allocated         Allocated (%)
   Class A           126               49              38%
   Class B         16383             7354              45%
   Class C       2097151            44014               2%

             Table 1: Network Number Statistics (May 1992) [2]

Class A and B network numbers are a limited resource, so allocations from that space are going to be restricted 🚫 The entire Class A number space stays with the IANA and the IR 🔒 No Class A network numbers will be allocated to distributed regional registries at this time. (See section 4.1.)

Class B allocations are restricted too 💜 Small blocks of numbers may be allocated to regional registries, which will need to make sure the allocation guidelines are met. The IR keeps an eye on those allocations 👀 (See section 4.2.)

It is proposed that the IR, and any designated regional registries, allocate addresses in line with this overall scheme. Where qualifying regional registries are established, primary responsibility for allocation within that block gets delegated to that registry. Worth noting: the Reseaux IP Europeens Network Coordination Center (RIPE NCC) already had a block of Class C addresses (193.0.0 - 193.255.255) before this proposal came along. The RIPE NCC agreed to allocate the addresses in that block according to the guidelines stated in this RFC 🙌

The Class C space gets divided into allocatable blocks, reserved by the IANA and the IR for allocation to distributed regional registries. If there are no designated regional registries in a geographic area, the IR assigns addresses to networks in that area according to the Class C allocation divisions 🧩

Looking at the Class C numbers, prefixes 192 and 193 are already assigned. The rest, from prefix 194 through 223, is mostly unassigned 🔍

The IANA and the IR will reserve the upper half of this space, which covers 208.0.0.0 through 223.255.255.255. Network numbers from this portion of the Class C space stay unallocated and unassigned until further notice 🔒

The rest of the Class C space will be allocated in a way that's compatible with potential address aggregation techniques. The plan is to divide this range into eight equally sized address blocks 🍰

      192.0.0.0 - 193.255.255.255
      194.0.0.0 - 195.255.255.255
      196.0.0.0 - 197.255.255.255
      198.0.0.0 - 199.255.255.255
      200.0.0.0 - 201.255.255.255
      202.0.0.0 - 203.255.255.255
      204.0.0.0 - 205.255.255.255
      206.0.0.0 - 207.255.255.255

Each block is 131,072 addresses, which is about 6% of the total Class C address space 🧮

The proposal is to use a broad geographic allocation for these blocks. At the moment there are four major areas of address allocation: Europe, North America, Pacific Rim, and South & Central America 🌏

Specifically, the top level block allocation should be designated like this:

   Multi-regional          192.0.0.0 - 193.255.255.255
   Europe                  194.0.0.0 - 195.255.255.255
   Others                  196.0.0.0 - 197.255.255.255
   North America           198.0.0.0 - 199.255.255.255
   Central/South
    America                200.0.0.0 - 201.255.255.255
   Pacific Rim             202.0.0.0 - 203.255.255.255
   Others                  204.0.0.0 - 205.255.255.255
   Others                  206.0.0.0 - 207.255.255.255

Same vibe as before: the IR and any designated regional registries allocate addresses in conformance with this overall scheme. Where qualifying regional registries are established, primary responsibility for allocation from within that block will be delegated to that registry 🫶

The "Others" ranges give flexibility for network number assignments outside the geographical regions that are already allocated 🌈 The multi-regional range covers network numbers that were assigned before this plan was put in place. The proposal is that the IANA and the IR adopt these divisions of the Class C network number space and begin assigning network numbers accordingly 🚀

4.0 Assignment of the Network Number Space 🧚

Running out of IP address space is a worry for the whole Internet community 😰 This plan for assigning Class A, B, or C IP numbers to network applicants has two major goals:

to reserve a portion of the IP number space so it's available to transition to a new numbering plan
to assign the Class C network number space in a way that's compatible with proposed address aggregation techniques

4.1 Class A 💖

The Class A number space can support the largest number of unique host identifier addresses, and it's also the class of network numbers that's the most sparsely populated 🌸 There are only about 11 Class A network numbers that are unassigned or unreserved, and those 11 represent about 9% of the total address space.

The IANA and the IR keep sole responsibility for assigning Class A network numbers 👑 The upper half of the Class A number space is reserved indefinitely (IP network addresses 64.0.0.0 through 127.0.0.0). New Class A assignments aren't expected in the near future, but any organization petitioning the IR for a Class A network number will be expected to provide a detailed technical justification documenting its network size and structure 📝 Class A assignments are at the IANA's discretion 💅

Part 2 is coming up next, bestie 🎀🫶

4.2 Class B 🌸

okay so back in the day, orgs were told to grab one subnetted Class B instead of a pile of Class Cs 📦. but Class Bs are super scarce now, and most orgs don't even use the whole Class B space, so the new vibe is: use multiple Class Cs where practical 💅

The restrictions on Class B allocation MAY cause some orgs to spend extra resources juggling multiple Class C numbers. ngl that's a bummer 😭 but it's kinda inevitable if we're gonna control who gets Class Bs. the whole goal is to balance those costs for the greater good of the Internet 🫶

4.2.1 🦋

Orgs applying for a Class B network number SHOULD fulfill the following criteria 📝

the organization presents a subnetting plan which documents more than 32 subnets within its organizational network

AND

the organization has more than 4096 hosts

Orgs applying for a Class B network number MUST submit an engineering plan that documents its need for a Class B network number. This document MUST demonstrate that it is unreasonable to engineer its network with a block of Class C network numbers. The engineering plan MUST include how many hosts the network will have within the next 24 months and how many hosts per subnet within the next 24 months. 📊

The submitted engineering plans will be held in strict confidence by the Internet registries and will only be used to judge whether an application is justified 🔒 If it is deemed that the applicant's engineering plan, including the number of hosts and subnets, does not warrant a Class B assignment, the applicant will be allocated a block of Class C addresses.

There MAY be some circumstances where the organization is unable to utilize a block of Class C network numbers and does not meet the suggested criteria. In such cases, the engineering plan SHOULD clearly demonstrate their inability to utilize a block of Class C network numbers 🙈

4.2.2 ✨

The IR MAY allocate small blocks of Class B network numbers to regional registries if so doing will improve the service that is being provided to the community 🌈 The IR MAY issue more specific guidelines for the further assignment of the numbers, which will be consistent with the stated guidelines. The IR MAY require accounting of the block assignment, including receipt of the applicants' engineering plans. And the IR MAY audit these engineering plans to confirm that the assignments are consistent with the guidelines 🔍

4.3 Class C 🎀

Section 3 of this document recommends a division of the Class C number space. That division is primarily an administrative division which lays the groundwork for distributed network number registries 🧱 This section addresses assignment of network numbers from within regional block assignments. Sub-allocations of the block to sub-registries is beyond the scope of this paper, so we're not going there today 🙅‍♀️

By default, if an organization requires more than a single Class C, it will be assigned a bit-wise contiguous block from the Class C space allocated for its geographic region 🗺️

For instance, a European organization which requires fewer than 2048 unique IP addresses and more than 1024 would be assigned 8 contiguous class C network numbers from the number space reserved for European networks, 194.0.0.0 - 195.255.255.255. If an organization from Central America required fewer than 512 unique IP addresses and more than 256, it would receive 2 contiguous class C network numbers from the number space reserved for Central/South American networks, 200.0.0.0 - 201.255.255.255 🌎

The IR or the registry to whom the IR has delegated the registration function will determine the number of Class C network numbers to assign to a network subscriber. That's based on the subscriber's 24 month projection of required end system addresses, using this lil chart 👇

        Organization                            Assignment
1) requires fewer than 256 addresses    1 class C network
2) requires fewer than 512 addresses    2 contiguous class C networks
3) requires fewer than 1024 addresses   4 contiguous class C networks
4) requires fewer than 2048 addresses   8 contiguous class C networks
5) requires fewer than 4096 addresses  16 contiguous class C networks
6) requires fewer than 8192 addresses  32 contiguous class C networks
7) requires fewer than 16384 addresses 64 contiguous class C networks

If the subscriber's network is divided into logically distinct LANs across which it would be difficult to use the given number of Class C network numbers, the above criteria MAY apply on a per-LAN basis 🧩 For example, if a subscriber has 600 hosts equally divided across ten Ethernets, the allocation to that subscriber could be ten Class C network numbers, one for each Ethernet. The subscriber would have to back up the request with an engineering plan if they want to deviate from the stated criteria 📋

These criteria are not intended to cause a subscriber to subnet Class C networks unnecessarily. Although, if a subscriber has a small number of hosts per subnet, the subscriber SHOULD investigate the feasibility of subnetting Class C network numbers rather than requesting one Class C network number for every subnet 🤓 In cases where the lack of Class C subnetting would result in an extravagant waste of address space, the registries MAY request an engineering plan detailing why subnetting is impossible.

If a subscriber has a requirement for more than 4096 unique IP addresses, it could conceivably receive a Class B network number. However, there are cases where a subscriber MAY request a larger block of Class C network numbers. For instance, if an organization requires fewer than 8192 addresses and requests 32 Class C network addresses, the regional registry MAY honor this request 🫶 The maximal block of Class C network numbers that SHOULD be assigned to a subscriber consists of 64 contiguous Class C networks. This would correspond to a single IP prefix of 18 bits 🧁

Exceptions from the above stated criteria will be determined on a case-by-case basis ⭐

5.0 Conclusion 💫

This proliferation of class C network numbers MAY aid in retarding the dispersion of class A and B numbers, but it is sure to accelerate the explosion of routing information carried by Internet routers 🚀 Inherent in these recommendations is the assumption that there will be modifications in the technology to support the larger number of network address assignments, due to the decrease in assignments of Class A and B numbers and the proliferation of Class C assignments.

Many proposals have been made to address the rapid growth of network assignments, and a discussion of those proposals is beyond the scope and intent of this paper 🙃

These recommendations for management of the current IP network number space only profess to delay depletion of the IP address space, not to postpone it indefinitely ⏳

6.0 Acknowledgements 🙏

The author would like to acknowledge the substantial contributions made by the members of the following two groups: the Federal Engineering Planning Group (FEPG) and the Intercontinental Engineering Planning Group (IEPG) 🌷 This document also reflects many concepts expressed at the IETF Addressing BOF, which took place in Cambridge, MA in July 1992. In addition, Dan Long (BBN), Jon Postel (ISI), and Yakov Rekhter (T.J. Watson Research Center, IBM Corp.) reviewed this document and contributed to its content 💜 The author thanks those groups and individuals who have been cited for their comments.

7.0 References 📚

[1] Cerf, V., "IAB Recommended Policy on Distributing Internet Identifier Assignment and IAB Recommended Policy Change to Internet 'Connected' Status", RFC 1174, CNRI, August 1990.

[2] Wang, Z., and J. Crowcroft, "A Two-Tier Address Structure for the Internet: A Solution to the Problem of Address Space Exhaustion", RFC 1335, University College London, May 1992.

Other related relevant work:

[3] "Internet Domain Survey", Network Information Systems Center, SRI International, July 1992.

[4] Solensky, F., and F. Kastenholz, "A Revision to IP Address Classifications", Work in Progress, March 1992.

[5] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Supernetting: an Address Assignments and Aggregation Strategy", RFC 1338, BARRNet, cisco, Merit, OARnet, June 1992.

[6] Rekhter, Y., and Li, T., "Guidelines for IP Address Allocation", Work in Progress, August 1992.

[7] Rekhter, Y. and Topolcic, C., "Exchanging Routing Information across Provider/Subscriber boundaries in CIDR environment", Work in Progress, February 1993.

8.0 Security Considerations 🔐

Security issues are not discussed in this memo. 💀

9.0 Author's Address 📮

Elise Gerich
Merit Network, Inc.
1071 Beal Avenue
Ann Arbor, MI 48109-2112

Phone: (313) 936-3335
EMail: epg@MERIT.EDU

and that's a wrap on RFC 1466, bestie 🌈✨👑

📦 where this page comes from

ietf: rfc1466 1993-05
💖 girlified by claude-haiku-5-5 on 2026-10-15: a language model's rewrite of the original, under its terms