Network

What is IPv4?

IPv4 is version 4 of the Internet Protocol, addressing hosts with 32 bits written as four dot-separated octets, which gives roughly 4.3 billion addresses. The top-level pool ran dry in 2011, pushing providers toward private addressing, carrier-grade NAT and a paid transfer market. Nearly all proxy traffic still runs over IPv4 because that is what target sites accept.

The header is 20 bytes without options and carries the source and destination addresses, a TTL that every router decrements, a protocol field naming TCP or UDP or something else, and a checksum over the header itself. Routing works on prefixes. A router matches the longest prefix it holds and forwards accordingly, so 203.0.113.0/24 can be handled separately from the larger block it sits inside. That longest-prefix rule is also why a small announcement can pull traffic away from the range around it.

IANA handed its last unallocated blocks to the regional registries in February 2011, and the registries drained their own pools over the years that followed. What remains is a secondary market. Blocks are bought and leased, priced per address, and a /24 is the smallest unit most networks will carry in the global routing table. Providers who cannot buy their way out run carrier-grade NAT instead, putting large numbers of subscribers behind a shared public address.

For anyone working with proxies, IPv4 is the space where reputation lives. Scoring services keep records per address and per /24, and a range announced by a hosting ASN is treated differently from one announced by a mobile carrier, regardless of who sends the traffic. Buying a fresh subnet does not reset that, because the block's history and its ASN follow it. Residential and mobile IPv4 holds its value because sites cannot block those ranges wholesale without losing real customers.

Day to day, IPv4 turns up in allowlists and firewall rules. IP authentication on a proxy account takes a /32 for a single machine or a wider prefix for an office, and a wrong mask either locks you out or opens the endpoint to a whole network. Dynamic home addresses complicate this further, since a router reboot can hand you a different address and break the allowlist you set the day before.

Where you meet it

IPv4 shows up whenever you configure access rather than read theory. You paste a /32 into an allowlist or whitelist a whole office range, then look at a rejected request and work out which /24 it came from. Price traces back to it too. Proxy pools are quoted in IPv4 because that is the scarce address family target sites accept, and a provider's cost per address is a real line item.

Common questions

How many IPv4 addresses are there?

Thirty-two bits give 4,294,967,296 combinations, and a sizeable share is reserved for private use, loopback, multicast and other special purposes, so the usable public pool is smaller. The total is fixed. The only ways to add capacity are IPv6 or sharing addresses through NAT.

Is IPv4 being phased out?

Not on any timeline worth planning around. Both protocols carry growing traffic, and enough services stay IPv4-only that operators run dual stack or translation rather than switching. For proxy work, expect IPv4 to remain the address family that target sites reliably accept.

Why do IPv4 proxies cost more than IPv6 ones?

Scarcity on one side, usefulness on the other. IPv4 blocks are bought or leased on a secondary market at a real per-address price, while IPv6 space is plentiful and cheap to obtain in bulk. Sites also accept and score IPv4, so an IPv6 address that many targets refuse is worth less to buyers.

Related terms

IPv6
IPv6 is version 6 of the Internet Protocol, addressing hosts with 128 bits written as eight hexadecimal groups, such as 2001:db8::1. The space is large enough that carriers assign each subscriber a whole subnet, usually a /64 or wider, so reputation systems score prefixes instead of single addresses. Adoption is broad but far from universal.
CGNAT
Carrier-grade NAT is address translation performed by an ISP rather than in the customer's router, putting many subscribers behind one public IPv4 address. Mobile networks depend on it. Each customer holds a private or shared-range address, usually from 100.64.0.0/10, and the carrier rewrites the source address and port on every outbound flow.
IP Address
An IP address is the numeric identifier a device presents on an IP network so packets can be routed to and from it. IPv4 writes 32 bits as four decimal octets, such as 203.0.113.7. IPv6 writes 128 bits as hexadecimal groups, such as 2001:db8::1. Every request a server logs is tied to one.
NAT
Network Address Translation rewrites the address and port fields of packets as they cross a router, letting many private hosts share one public IP. The router keeps a translation table, mapping each outbound flow to a free public port and reversing the rewrite on replies. Home routers do this for a household; carriers do it for whole regions.
ASN
An Autonomous System Number identifies a network that announces its own IP address ranges to the rest of the internet through BGP. Every routable address sits inside a prefix announced by some AS, so the ASN behind an IP tells you who operates it - a mobile carrier, a hosting provider, a home ISP or a corporate network.
DNS
The Domain Name System turns a hostname such as example.com into the IP addresses a client can connect to. A stub resolver on the device asks a recursive resolver, which walks the root, TLD and authoritative name servers, then caches the answer for the record's TTL. Queries travel on port 53, or over TLS or HTTPS when encrypted.
DNS Leak
A DNS leak happens when a client sends its name lookups outside the proxy tunnel, so queries travel over the real ISP connection while the traffic itself exits on the proxy IP. The resolver operator, and any authoritative server it contacts, then sees a lookup tied to your actual network, region and provider.
WebRTC Leak
A WebRTC leak is a browser exposing your real IP address through its peer-to-peer connection API while page traffic goes through a proxy. WebRTC gathers ICE candidates over its own UDP sockets, which ignore the browser's proxy configuration, and any script on the page can read those candidates without asking permission.

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