IPv4 Block Size Cheat Sheet: /24 to /16 with Lease Pricing

Picking the wrong IPv4 block size is a quiet, expensive mistake. You either over-lease and overpay, or under-lease and find yourself back in the market in six months. This is a quick reference to get the decision right the first time. The Math, Fast Every IPv4 block size follows the same formula: 2^(32 - prefix length) total addresses, minus 2 reserved (network + broadcast) = usable hosts. CIDR Total IPs Usable IPs /24 equivalents /24 256 254 1 /23 512 510 2 /22 1,024 1,022 4 /21 2,048 2,046 8 /20 4,096 4,094 16 /19 8,192 8,190 32 /18 16,384 16,382 64 /17 32,768 32,766 128 /16 65,536 65,534 256 Hard floor to know: /24 is the minimum BGP-routable prefix in the RIPE NCC service region. Sub-/24 blocks are filtered by the vast majority of BGP peers and won't propagate across the public internet. If you only need 30 external IPs, you still lease a full /24. Cost per IP by Block Size (RIPE Region) Larger blocks = lower per-IP monthly rate, but the savings curve flattens fast: Block Total IPs Est. monthly Per IP/month /24 256 from ~€180 ~€0.70 /23 512 from ~€330 ~€0.65 /22 1,024 from ~€620 ~€0.61 /21 2,048 from ~€1,150 ~€0.56 /20 4,096 from ~€2,050 ~€0.50 Prices are illustrative. Actual rates vary by block reputation, availability, and lease term. The per-IP delta between a /24 and a /22 is small. Lease term length often has a bigger impact on total cost - a 12-month /24 can undercut a month-to-month /22. Which Block Size for Which Use Case Shared/web hosting: Start with /24, segment customers per /24 for cleaner blacklist management and abuse isolation. Dedicated servers (50-100 nodes, multiple IPs each): /22 or /21 - account for IPMI interfaces, management ranges, and customer allocations from the start. Proxy/VPN rotation pools: Address diversity drives value here. /21 to /20 for production scale; /23 to /22 for pilots. Always check IP reputation history before leasing - it matters more here than anywhere else. Enterprise multi-site: Minimum one /24 per physical site. Use /22 or /21 aggregates for clean BGP summarization across locations. Three Things That Trip People Up 1. /22 ≠ guaranteed routing flexibility A /22 can be announced as a single aggregate prefix. Deaggregating into /24s for traffic engineering is possible, but whether your upstream allows it is a different question. Verify before you commit. 2. Reputation travels with the block Always check the block's abuse history on Spamhaus, Barracuda BRBL, or via MXToolbox before signing a lease. A cheap /22 with a dirty history will cost you more in operational pain than it saves in rent. 3. RIPE's 24-month transfer lock applies to purchases, not leases If you buy rather than lease, transferred addresses can't be re-transferred for 24 months under RIPE policy. Leasing sidesteps this entirely. For the full breakdown - including an interactive IPv4 CIDR calculator, a use-case decision framework, and detailed guidance on lease pricing - check out the complete guide on the IPbnb blog: IPv4 Subnet Calculator: How to Choose the Right Block Size for Your Project →