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What Is IPv4?

IPv4 (Internet Protocol version 4) is the addressing system that still carries most internet traffic. An IPv4 address is 32 bits long and written as four numbers from 0 to 255 separated by dots, such as 203.0.113.45, which allows about 4.3 billion addresses in total.

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how it works

How IPv4 addresses work

Each of the four numbers is an octet: 8 bits, so 0 to 255. Together they make 32 bits, or 2^32 = 4,294,967,296 possible addresses. Part of the address names the network and the rest names a host inside it; the split is set by the subnet mask or CIDR prefix, such as /24.

IPv4 was specified in RFC 791 in 1981, long before anyone expected billions of phones and laptops. Large parts of the space are reserved for special purposes and never appear as a public address on the internet.

  • 1

    10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16

    Reserved for
    Private networks (RFC 1918)
    Seen by websites?
    No, they stay inside homes and offices
  • 2

    100.64.0.0/10

    Reserved for
    Carrier-grade NAT inside ISPs (RFC 6598)
    Seen by websites?
    No, the carrier's public IP is seen
  • 3

    127.0.0.0/8

    Reserved for
    Loopback: the machine itself
    Seen by websites?
    No
  • 4

    224.0.0.0/4

    Reserved for
    Multicast
    Seen by websites?
    No
why it matters

Why IPv4 matters for proxy users

IPv4 ran out. IANA handed its last blocks to the regional registries in February 2011, and the registries for North America and Europe ran out of free space in 2015 and 2019. New networks now buy or lease addresses from others, so every IPv4 address has a real market price.

CleanProxies static ISP proxies are dedicated IPv4 addresses on US carrier networks, and ISP subnet proxies are whole IPv4 /24 blocks.

IPv4: what it means for you
  • Price: a dedicated IPv4 proxy costs more than an IPv6 one because the address itself is scarce. A low per-IP price on IPv6 is not a like-for-like comparison.
  • Reach: every public website accepts IPv4 connections; many still do not accept IPv6. An IPv4 proxy works everywhere.
  • History: anti-fraud systems have years of reputation data per IPv4 address and per /24 subnet, so a clean IPv4 address carries real weight.
  • Allowlists: firewalls, APIs and the IP whitelisting on most proxy services expect IPv4 addresses or ranges.

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Related terms

Terms that come up alongside IPv4.

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IPv4 FAQs

Straight answers about IPv4.

2^32, which is 4,294,967,296. Several hundred million of them are reserved for private networks, multicast, loopback and other special uses, so fewer are usable on the public internet.

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