IPv4

1.0 Format

IPv4 is an identifier with a fixed length of 32-bit (2³²), which can represent about 4.3 billion different values¹:

The human readable and easily memorable dot-decimal notation, which is also used in technical environments, groups the address into four parts where each consists of an unsigned decimal number with 8 bit:

An unsigned 8-bit decimal number can reflect 256 (2⁸) different values (0-255). Since an address has four parts using such a number, its total length corresponds to 32 bit:

Working with 8-bit parts were the basis for a classful network design which was the standard in the 1980s. It divided the space into 8-bit groups (8, 16, and 24 bit) which were called Class A, B and C. This lead to inefficient assignments because a /8 subnet already had 16 777 216 addresses, while a /16 only had 65 536 addresses.

2.0 CIDR Table / Calculator

The classful network design was already replaced in the 1990s with a classless network design, which is called Classless Inter-Domain Routing (CIDR). It divides the space using 1-bit steps, as seen in the chart below:

• • Prefix
  • IP Addresses
  • /29s/28s/27s/26s/25s/24s/23s/22s/21s/20s/19s/18s/17s/16s/15s/14s/13s/12s/11s/10s/9s/8s
  • /24s
  • /16s
  • /8s
  • Subnet Mask

• • /32²
  • 1
  • 0
  • 0
  • 0
  • 0
  • 255.255.255.255
• • /31
  • 2
  • 0
  • 0
  • 0
  • 0
  • 255.255.255.254
• • /30
  • 4
  • 0
  • 0
  • 0
  • 0
  • 255.255.255.252
• • /29
  • 8
  • 1
  • 0
  • 0
  • 0
  • 255.255.255.248
• • /28
  • 16
  • 2
  • 0
  • 0
  • 0
  • 255.255.255.240
• • /27
  • 32
  • 4
  • 0
  • 0
  • 0
  • 255.255.255.224
• • /26
  • 64
  • 8
  • 0
  • 0
  • 0
  • 255.255.255.192
• • /25
  • 128
  • 16
  • 0
  • 0
  • 0
  • 255.255.255.128
• • /24³
  • 256
  • 32
  • 1
  • 0
  • 0
  • 255.255.255.0
• • /23
  • 512
  • 64
  • 2
  • 0
  • 0
  • 255.255.254.0
• • /22
  • 1 024
  • 128
  • 4
  • 0
  • 0
  • 255.255.252.0
• • /21
  • 2 048
  • 256
  • 8
  • 0
  • 0
  • 255.255.248.0
• • /20
  • 4 096
  • 512
  • 16
  • 0
  • 0
  • 255.255.240.0
• • /19
  • 8 192
  • 1 024
  • 32
  • 0
  • 0
  • 255.255.224.0
• • /18
  • 16 384
  • 2 048
  • 64
  • 0
  • 0
  • 255.255.192.0
• • /17
  • 32 768
  • 4 096
  • 128
  • 0
  • 0
  • 255.255.128.0
• • /16
  • 65 536
  • 8 192
  • 256
  • 1
  • 0
  • 255.255.0.0
• • /15
  • 131 072
  • 16 384
  • 512
  • 2
  • 0
  • 255.254.0.0
• • /14
  • 262 144
  • 32 768
  • 1 024
  • 4
  • 0
  • 255.252.0.0
• • /13
  • 524 288
  • 65 536
  • 2 048
  • 8
  • 0
  • 255.248.0.0
• • /12
  • 1 048 576
  • 131 072
  • 4 096
  • 16
  • 0
  • 255.240.0.0
• • /11
  • 2 097 152
  • 262 144
  • 8 192
  • 32
  • 0
  • 255.224.0.0
• • /10
  • 4 194 304
  • 524 288
  • 16 384
  • 64
  • 0
  • 255.192.0.0
• • /9
  • 8 388 608
  • 1 048 576
  • 32 768
  • 128
  • 0
  • 255.128.0.0
• • /8
  • 16 777 216
  • 2 097 152
  • 65 536
  • 256
  • 1
  • 255.0.0.0
• • /7
  • 33 554 432
  • 4 194 304
  • 131 072
  • 512
  • 2
  • 254.0.0.0
• • /6
  • 67 108 864
  • 8 388 608
  • 262 144
  • 1 024
  • 4
  • 252.0.0.0
• • /5
  • 134 217 728
  • 16 777 216
  • 524 288
  • 2 048
  • 8
  • 248.0.0.0
• • /4
  • 268 435 456
  • 33 554 432
  • 1 048 576
  • 4 096
  • 16
  • 240.0.0.0
• • /3
  • 536 870 912
  • 67 108 864
  • 2 097 152
  • 8 192
  • 32
  • 224.0.0.0
• • /2
  • 1 073 741 824
  • 134 217 728
  • 4 194 304
  • 16 384
  • 64
  • 192.0.0.0
• • /1
  • 2 147 483 648
  • 268 435 456
  • 8 388 608
  • 32 768
  • 128
  • 128.0.0.0
• • /0
  • 4 294 967 296
  • 536 870 912
  • 16 777 216
  • 65 536
  • 256
  • 0.0.0.0

3.0 Exhaustion

While the IPv4 address space theoretically has more than 4.3 billion IP addresses, only 3.7 billion are available for public use because the rest is reserved for special purposes (e.g. 224/4 for multicast) or future use (240/4)⁴.

Due to this scarcity companies started to lease or buy IPv4 addresses from Local Internet Registries (LIRs).

August 1990 – Based on statistics, it was feared that an exhaustion of the pool could happen in 1994–1998.⁵

October 2002 – IANA had 73 /8 blocks left, which is equivalent to 1 224 736 768‬ (1.22 billion) IPv4 addresses.⁶

August 2004 – The available pool at IANA increased to 77 /8 blocks, which is equivalent to 1 291 845 632‬ (1.29 billion) IPv4 addresses.⁷ This is related to the blocks 173/8–187/8 which were previously allocated to Various Registries in 1993, but seems to be returned to IANA in April 2003.

May 2008 – IANA had 40 /8 blocks left, which is equivalent to 671 088 640 (671 million) IPv4 addresses.⁸

February 2011 – IANA assigned the last five available /8 blocks equally to all five RIRs⁹. AFRINIC received 102/8, APNIC 103/8, ARIN 104/8, LACNIC 179/8 and RIPE NCC 185/8¹⁰.

April 2011 – APNIC reached the last /8 block (103/8).¹¹

March 2012 – RIPE NCC reached the last /8 block (185/8) and moved to an only one /22 per LIR policy.¹²

May 2012 – The ICANN board ratified the Global Policy for Post Exhaustion IPv4 Allocation Mechanisms by the IANA which regulates the distribution of address space returned to IANA: […] its size is not expected to be so large but substantial enough to be able to consider an additional minimum allocation for APNIC members.¹³

June 2014 – LACNIC reported its (relatively) exhaustion because they reached the last /10 block¹⁴, so the further allocation rate has been greatly reduced¹⁵. Since there is still space available which will probably last until May 2020¹⁶, new members were still eligible to receive their initial /24 or /22 allocation in 2019.

July 2015 – RIPE NCC changed its policy in order to block transfers of allocations made to members for a period of 24 months. The reason for that change was a proposal which stated that speculators had opened new LIR accounts only to sell the initial /22 allocation given according to the one /22 per LIR policy.¹⁷

September 2015 – ARIN finally allocated all available IPv4 addresses.¹⁸ Further requests can only be fulfilled by using recovered space (e.g. revoked space due to non-payments) and are handled through a waiting list. ARIN was the first RIR who became (absolutely) exhausted.

November 2015 – The RIPE NCC Executive Board decided to temporarily restrict the ability for members to create multiple LIR accounts because it was considered as not conform to the policy.¹⁹

May 2016 – The members of the RIPE NCC General Meeting voted for a resolution which removed the previously applied restrictions which temporarily blocked members from creating multiple LIR accounts.²⁰ Prior to this, some organizations already circumvented the restrictions by simply creating new business entities.²¹

January 2017 – AFRINIC entered IPv4 Exhaustion Phase 1/2.²²

April 2018 – RIPE NCC allocated the last addresses from the last 185/8²³. Since then they have started to allocate from over nine million recovered IPv4 addresses (about a IPv4 /9).

July 2019 – AFRINIC had about 5.15 million addresses left²⁴ in 2019, which is equivalent to IPv4 /10 + /12 or 5 034 x IPv4 /22. AFRINIC is the RIR with the most IPv4 addresses left in 2019.²⁵

August 2019 – RIPE NCC announced that the available pool is nearing the end.²⁶

October 2019 – On 2nd October 2019 the RIPE NCC reported that they allocated the last contiguous /22 IPv4 address block and that they have reached a point where the number of LIRs waiting to be activated was larger than the number of /22 equivalents remaining. At this point, the available pool decreased to about 1.01 million addresses.²⁷ As a result new LIRs and some LIRs which were still waiting for their account activation wouldn't receive any space at all and so only be eligible to request a /24 via the waiting list. However, as long addresses in form of /22 equivalents were still left, existing (activated) members were still able to request their final subnet(s) as long they didn't already receive the final /22 equivalent before.²⁸

November 2019 – Exhaustion of the RIPE NCC. On 25th November 2019 they made the final /22 IPv4 allocation of the last remaining addresses.²⁹ The waiting list was introduced. Only LIRs which never received an IPv4 allocation before are eligible to receive one IPv4 /24 allocation through the waiting list.

January 2020 – Between 25th November 2019 and 12th January 2020, due to the exhaustion, the amount of LIRs in the waiting list queue – waiting for their one-time IPv4 /24 allocation – was greater than zero³⁰. Between 12th January 2020 and 17th November 2021, new LIRs were able to receive their one-time IPv4 /24 allocation without delay, because the RIPE NCC was able to recover space. On 18th November 2021, all of the recovered space got allocated, so that new LIRs are going to be added to the waiting list again.

4.0 Current Distribution