Carrier-Grade NAT vs Dedicated IPv4: ISP Cost Guide

CGNAT vs. dedicated IPv4 might be the single most expensive decision an ISP makes this decade. IPv4 has settled into the $40–$60 per address range in 2024–2025, and the free pools at the Regional Internet Registries are, for all practical purposes, gone. If your subscriber base keeps growing — and it better — you’re left with two options: stretch what little public space you have with CGNAT, or buy in at market rates. Both work. Neither is free. Here’s what the numbers actually look like, with the risks included, so you can build a procurement case that survives contact with your CFO.

What Is Carrier-Grade NAT and Why ISPs Adopt It

Carrier-Grade NAT (CGNAT, defined in RFC 6598) lets an ISP put thousands of subscribers behind a single public IPv4 address using a NAT444 architecture. The customer doesn’t get a routable public IP. Instead, the ISP hands out private or shared address space — usually 100.64.0.0/10 — on the access network, and translates everything at the edge.

The economics are hard to ignore. Take a mid-sized ISP adding 10,000 subscribers. That’s roughly a /19 (8,192 addresses), which at today’s prices means something like $330,000–$490,000 out the door. Run CGNAT at a conservative 500:1 reuse ratio — some operators push 1,000:1 — and the same growth fits on 10–20 public addresses. Twenty.

• Hardware savings: Modern CGNAT-capable routers and session border gateways chew through millions of concurrent translations, and NAT capacity is often just a line card away rather than a whole new platform.
• Faster time-to-market: No brokers, no transfer approvals, no RIR justification paperwork. CGNAT can go live in weeks.
• Future-proofing: Address conservation pairs naturally with an IPv6 transition like 464XLAT or DS-Lite.

The trade-offs are just as well documented. Port-forwarding breaks. Geolocation gets fuzzy — sometimes badly so. Abuse handling gets heavier, because when fifty customers share one address, every complaint needs log correlation to untangle. And there’s the logging obligation itself under data-retention rules. Practical advice: budget for a solid syslog or IPFIX pipeline from day one, and consider a hybrid where business customers get dedicated IPv4 while residential rides CGNAT.

Dedicated IPv4: Costs, Scarcity, and Market Pricing

Dedicated IPv4 means every subscriber (or service) gets a globally routable address from a block your organization holds or leases. Since IANA ran dry in 2011 and all five RIRs followed, the only supply left is the secondary market — transfers and leases.

Current market benchmarks

• Purchase: /22 blocks (the minimum transferable unit in most RIR regions) trade at $40–$60 per IP. Call it $180,000–$265,000 per /22, depending on region and how clean the block’s history is.
• Lease: Monthly leasing runs roughly $0.30–$0.60 per IP — attractive if you’re bridging a capital crunch or covering short-term growth.
• Hidden costs: RIR transfer fees, legal due diligence, blacklist remediation, and escrow services of the BrokerCoin variety. Figure another 2–5% on top.

One thing worth sitting with: scarcity isn’t going away, and IPv6 adoption remains slow in plenty of markets. That’s turned dedicated IPv4 into something closer to an asset than an expense. Blocks bought years ago have historically held their value — or appreciated.

Carrier-Grade NAT vs IPv4: A Head-to-Head Cost Comparison

Let’s make it concrete. Same 10,000-subscriber expansion, two paths:

• CGNAT path: $50,000–$150,000 in hardware and licensing, plus ongoing logging and support overhead. Roughly 60–80% cheaper upfront than buying equivalent space.
• Dedicated IPv4 path: $330,000–$490,000 to acquire (or $3,000–$6,000/month leased), with near-zero per-subscriber infrastructure overhead and full service transparency.
• Breakeven horizon: Stretch it to 5–7 years and purchased IPv4 often wins on total cost of ownership — because the addresses keep their resale value, the net cost ends up far below the sticker price.

Support costs pull in the other direction, though. CGNAT deployments typically generate 5–15% more Tier-1 tickets — gaming NAT issues, remote access setups, VoIP quirks. Price that against your helpdesk’s fully loaded cost per ticket before you commit. For most operators, the honest answer is a deliberate hybrid: CGNAT for the residential mass market, dedicated IPv4 for premium and business tiers. It’s a strategy the verified sellers and competitive pricing at IP4 Market make straightforward to execute.

Performance Trade-offs: Latency, Port Exhaustion, and User Experience

The performance gap between Carrier-Grade NAT and plain IPv4 is subtler than most people expect. The NAT44 translation itself adds almost nothing — well under a millisecond in most deployments. The trouble sits elsewhere. It sits in port allocation and connection tracking. A CGNAT gateway serving thousands of subscribers can run its state table dry during evening peaks, and when that happens you get dropped sessions, gaming connections that fail mid-match, and voice calls that break in ways users always blame on “the internet.” VoIP and WebRTC suffer first, since both are unforgiving about NAT traversal problems.

Port exhaustion is worth dwelling on. Under a traditional NAT44 pool, a subscriber might get 1,000 to 4,000 ports. That sounds generous until an application starts flinging connections around — torrent clients do this, so do cloud sync tools and video conferencing platforms. A single heavy user can burn through their allocation faster than support can answer the ticket. My advice: run deterministic NAT (D-NAT) with port-block logging instead of dynamic allocation. It cuts logging overhead by up to 90% and still lets you answer abuse reports and lawful intercept requests when they arrive.

• Watch per-subscriber port usage and raise allocations before the complaints do it for you.
• Turn on endpoint-independent mapping (EIM) — gaming consoles and peer-to-peer apps will thank you.
• Keep dedicated IPv4 aside for latency-sensitive tiers, business SIP trunks and hosted PBX above all.

Compliance, Geolocation, and Security Considerations

Performance is only half the story. The regulatory side weighs just as heavily on the Carrier-Grade NAT vs IPv4 decision, and it’s the half operators tend to underestimate. Shared address space creates legal exposure. When law enforcement comes asking who was behind a given IP at a given time, you must produce accurate port-to-subscriber logs — often on tight statutory deadlines. Several European jurisdictions layer data retention rules on top of NAT logging, which means storage bills and compliance work you didn’t plan for. Do that math before you deploy, not after.

Then there’s geolocation. A recurring headache, in my experience. Shared addresses get flagged by geolocation databases as data centers or VPN exits, and suddenly your subscribers are facing CAPTCHAs, content blocks, and refused signups on streaming, banking, and e-commerce sites. Premium customers notice this within days. Dedicated IPv4 blocks behave differently — especially blocks with a clean RIR history and established SWIP/WHOIS records. They geolocate reliably and carry the reputation of their prior legitimate use.

Security teams have their own gripe with CGNAT: DDoS mitigation and abuse handling get messy. Block one misbehaving address and you may take down hundreds of innocent subscribers with it. Dedicated IPv4 lets you blacklist precisely, without collateral damage — which is exactly why enterprise customers with security requirements write non-shared addressing into their SLAs.

Conclusion: Choosing the Right Addressing Strategy for Your ISP

So, CGNAT or IPv4? Wrong question. It’s a portfolio decision, not a binary one. CGNAT gives you capital efficiency that’s hard to argue with on price-sensitive residential tiers — per-subscriber addressing costs shrink to a few dollars. Dedicated IPv4 gives you reliability, clean geolocation, simpler compliance, and the service quality that wins business contracts and justifies premium pricing. Most sustainable operators I know run both: CGNAT as the default, with a growing dedicated pool reserved for business services, premium tiers, and anyone willing to pay for it.

Whichever ratio you land on, remember this: the quality of the blocks you buy matters as much as the quantity. Dirty addresses — abuse history, disputed ownership — will cost you more than any discount saved. Source from a marketplace with verified sellers, clean registry history, and honest pricing (IP4 Market is one such option) before you build out your dedicated inventory. Then plan the hybrid architecture deliberately, keep monitoring, and let the addressing strategy grow with your subscriber base.