How IP Addresses Are Assigned? 10 Key Steps (2025 Guide)

Short answer: IP addresses are allocated top‑down. IANA manages the global pool, delegates large blocks to Regional Internet Registries (RIRs), which allocate to ISPs and organizations. Your home router then assigns local addresses using DHCP (IPv4) or SLAAC/DHCPv6 (IPv6). Whether your public IP is static or dynamic affects stability, geolocation, and how services reach you.

The global hierarchy (who allocates what)

The public internet uses a carefully governed hierarchy to keep addresses unique and routable:

1. IANA (Internet Assigned Numbers Authority): maintains the global pool of IPv4 and IPv6 address space and delegates large blocks to RIRs.
2. RIRs (Regional Internet Registries): five non‑profits manage address space within regions: ARIN (North America), RIPE NCC (Europe/Middle East/Central Asia), APNIC (Asia‑Pacific), LACNIC (Latin America/Caribbean), AFRINIC (Africa).
3. NIRs/LIRs/ISPs: in some regions, National or Local Internet Registries handle allocations to ISPs, enterprises, universities, and hosts.
4. Organizations and end‑users: receive provider‑aggregatable (PA) or provider‑independent (PI) blocks for networks and services.

10 key steps from IANA to your device

1. IANA assigns to RIRs: large IPv4/IPv6 blocks are allocated to each region based on need and policy.
2. RIR policy review: members set policies (justification, conservation) that govern downstream allocations.
3. RIR allocates to ISPs/LIRs: ISPs receive routable blocks and register them in public databases (WHOIS/RDAP).
4. ISP plans address topology: subnets/prefixes are carved by geography, technology (FTTH, cable, mobile), and service tiers.
5. Routing announcements: ISPs announce prefixes via BGP to make them globally reachable.
6. Customer assignment: subscribers get public IPv4/IPv6 (dynamic or static) and local private ranges for LANs.
7. Home gateway allocates LAN IPs: DHCP (IPv4) and SLAAC/DHCPv6 (IPv6) assign device addresses and default routes.
8. Lease and renewal: DHCP leases expire and renew; IPv6 privacy extensions rotate interface IDs to reduce tracking.
9. Reverse DNS & records: ISPs maintain PTR (in‑addr.arpa/ip6.arpa) and other metadata used by mail and security systems.
10. Monitoring & updates: allocations, contact data, and route objects are maintained in RIR databases and routing registries.

Static vs dynamic: what changes for you

IPv4 vs IPv6 assignment

IPv4 (32‑bit) is scarce; ISPs often use CGNAT (Carrier‑Grade NAT) to place many customers behind one public IP while giving private RFC1918 addresses on the LAN. Port forwarding is limited or unavailable under CGNAT.

IPv6 (128‑bit) offers abundant addressing. ISPs typically provide a /56 or /64 prefix to homes. Devices form addresses via SLAAC with privacy extensions (temporary random interface IDs) or receive addresses via DHCPv6. You can subnet internally without NAT, which simplifies end‑to‑end connectivity (but requires proper firewalling).

What determines your geolocation & reputation

• Who owns the block: geolocation providers map WHOIS/RDAP data, usage patterns, and signals from apps/sites.
• Routing and latency: where a prefix is announced and peered can affect inferred city/region.
• Mobile vs residential vs data center: each type has a distinct risk/abuse profile and may be treated differently by services.
• Reputation feeds: spam, abuse reports, and blacklists impact deliverability (email) and fraud scoring.

Config examples: how your LAN gets its addresses

IPv4 DHCP

1. Router runs a DHCP server (scope like 192.168.1.100–192.168.1.199).
2. Device requests an address; router offers an IP, gateway, DNS, and lease time (e.g., 24 hours).
3. Device renews the lease before expiry to keep the same address.

IPv6 SLAAC/DHCPv6

1. ISP delegates a prefix (e.g., 2001:db8:1234::/56).
2. Router advertises subnets (RD/RA). Devices self‑configure via SLAAC with random interface IDs (privacy extensions).
3. Optionally, DHCPv6 provides DNS and additional settings; static addresses can be assigned for servers.

Common pitfalls & how to avoid them

• Exposed services on public IP: don’t expose admin panels; prefer VPN; enforce MFA and strong passwords.
• UPnP opening ports silently: disable or audit monthly; remove unknown mappings.
• Misleading geolocation: contact providers to correct, or use VPN when location sensitivity matters.
• Mail deliverability: set correct PTR, SPF, DKIM, DMARC when running outbound mail.
• Static IP privacy: consider per‑service profiles, strict cookie hygiene, and DoH/DoT.

Checklist — 12 practical actions

1. Ask your ISP whether you have static or dynamic public IP; request details about IPv6 prefix size.
2. Enable IPv6 privacy extensions; use DHCPv6 or SLAAC appropriately.
3. Disable WAN admin on the router; keep firmware updated.
4. Turn off UPnP unless you truly need it; review port forwards quarterly.
5. Prefer VPN instead of exposing services to the internet.
6. Segment IoT on a guest/VLAN network; keep work devices separate.
7. Use strong unique passwords and MFA for any remote access or admin accounts.
8. If you run email services, configure PTR/SPF/DKIM/DMARC and monitor blacklists.
9. Review your geolocation in critical apps; request corrections if consistently wrong.
10. Understand CGNAT limitations; consider business/static plans if you need inbound ports.
11. Monitor logs for failed logins and unusual traffic; enable alerts where possible.
12. Back up router configs; keep an offline copy and test restore.

FAQ

Who decides which IP I get at home?

Your ISP assigns your public IP (dynamic or static). Inside your home, your router assigns local addresses via DHCP (IPv4) and SLAAC/DHCPv6 (IPv6).

Why does my IP change after reboot?

Dynamic IPv4/IPv6 leases expire; on reboot you may receive a new address. ISPs also rotate IPs for address conservation or policy.

Can I request a static IP?

Many ISPs offer static or sticky IPs for a fee. Static IPs are useful for hosting/whitelists but can reduce privacy.

Do I still need NAT with IPv6?

No. IPv6 supports end‑to‑end addressing. Keep your firewall on and only allow inbound connections you intend to expose.

Why is geolocation for my IP wrong?

Providers infer location from ownership and routing signals which may be stale. Request dataset updates or use a VPN for location‑sensitive tasks.

Next steps: confirm your public IP, review router DHCP/DHCPv6 settings, and apply the checklist above.