Carrier-grade NAT has quietly become the default answer for organizations that ran out of IPv4 space years ago. And to be fair, it works \u2014 thousands of subscribers squeezed through a handful of shared addresses, problem solved. But it does so by trading short-term savings for long-term operational friction, and that trade rarely shows up in the capex forecast. In this article, I’ll run the numbers on both sides of the equation and lay out how to build a realistic business case for acquiring public IPv4 space.<\/p>\n
On a spreadsheet, CGNAT looks cheap. A few carrier-grade NAT gateways, some added state capacity, and you can serve thousands of customers per public address. But the true cost lives in the line items that never make it into anyone’s forecast.<\/p>\n
Every NAT session is a potential failure point. Port exhaustion causes dropped connections, application timeouts, and the classic “it works on my neighbor’s connection” support ticket. ISPs running large-scale CGNAT consistently report higher per-subscriber support costs \u2014 particularly from gamers, remote workers, and smart-home users whose applications simply assume end-to-end connectivity.<\/p>\n
When thousands of subscribers share one public IP, that address’s reputation becomes a shared liability. One subscriber sending spam can blackhole the whole block, breaking email delivery and triggering CAPTCHAs for everyone behind it. Reputation scrubbing, abuse complaints, RBL delisting \u2014 it’s an ongoing operational tax, and it never goes away.<\/p>\n
CGNAT obligates you to keep detailed address and port mapping logs (A+P or NAT44 logging) to answer law enforcement and abuse inquiries. Storage at line rate for session logs is non-trivial. Retention requirements vary by jurisdiction, which makes it worse. This is pure compliance cost with zero revenue upside.<\/p>\n
Inbound connections, port forwarding, self-hosted services, VoIP quality, geolocation accuracy \u2014 all of it degrades behind CGNAT. Premium subscribers increasingly expect a public IP as a baseline feature. Many ISPs now charge extra for it. If that’s you, ask yourself: how much revenue are you leaving on the table?<\/p>\n
Let’s model a mid-size ISP with 20,000 subscribers and a 16:1 CGNAT oversubscription ratio. That’s roughly 1,250 public IPv4 addresses today (about 4 \/24 blocks) versus a full public deployment.<\/p>\n
| Cost Factor<\/th>\n | Carrier-Grade NAT<\/th>\n | Public IPv4<\/th>\n<\/tr>\n<\/thead>\n |
|---|---|---|
| Hardware \/ CGNAT gateways<\/td>\n | $40,000\u2013$120,000 (plus refresh cycles)<\/td>\n | Minimal additional hardware<\/td>\n<\/tr>\n |
| Address acquisition (4 \u00d7 \/24)<\/td>\n | $0 upfront<\/td>\n | $100,000\u2013$160,000 one-time (at ~$25\u2013$40\/IP)<\/td>\n<\/tr>\n |
| Session logging & storage<\/td>\n | $5,000\u2013$15,000\/year<\/td>\n | Negligible<\/td>\n<\/tr>\n |
| NAT-related support overhead<\/td>\n | Higher per-subscriber cost<\/td>\n | Baseline support costs<\/td>\n<\/tr>\n |
| Resale value of assets<\/td>\n | None (depreciating hardware)<\/td>\n | IPv4 is an appreciating, transferable asset<\/td>\n<\/tr>\n |
| Premium “static IP” revenue<\/td>\n | Constrained<\/td>\n | New upsell opportunity<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n Here’s the key insight, and it’s the one most finance teams miss: IPv4 addresses are not an expense. They’re a capital asset. Unlike CGNAT hardware that depreciates to zero, a \/24 bought today has historically held or increased in value. Factored in properly, many organizations effectively “rent” their address space for free.<\/p>\n What IPv4 Addresses Cost in Today’s Market<\/h2>\nIPv4 prices have stabilized in recent years after peaking above $50 per address. Current market transactions typically settle in the $25\u2013$40 per address range<\/strong> for clean, RIR-transferred blocks. What moves the price?<\/p>\n A credible business case combines four levers:<\/p>\n For most ISPs above roughly 5,000 subscribers, the payback period on a public IPv4 migration is 2\u20134 years<\/strong>. Shorter if you monetize static IP add-ons.<\/p>\n Source blocks through a reputable marketplace with verified ownership, clean history, and escrow-protected transfers. Working with a trusted platform like IP4 Market<\/em>, which vets every seller and handles RIR transfer paperwork end to end, dramatically reduces transaction risk compared to private deals.<\/p>\n File the RIR transfer early \u2014 processing takes weeks to months. Update your IRR objects and RPKI ROAs, and coordinate with upstreams so the new prefixes route cleanly on day one.<\/p>\n Move new subscribers and premium tiers to public IPs first. This generates early revenue, shrinks CGNAT session load, and lets you decommission gateway capacity incrementally rather than in one disruptive cutover.<\/p>\n IPv6 deployment reduces your future IPv4 demand curve. The smartest migrations pair IPv4 acquisition now with aggressive IPv6 rollout, so your address needs peak and then decline.<\/p>\n Is migrating away from carrier-grade NAT worth it for small ISPs?<\/strong> Can I lease IPv4 addresses instead of buying?<\/strong> How long does an IPv4 transfer take?<\/strong> Carrier-grade NAT is a bridge technology, and the economics increasingly favor crossing that bridge sooner rather than later. Avoided operational costs, new premium-IP revenue, and the balance-sheet value of a transferable asset \u2014 public IPv4 is one of the few infrastructure investments that pays you back twice. Whether you buy or lease, platforms like IP4 Market offer verified sellers, escrow-protected transfers, and competitive market pricing to keep the migration low-risk.<\/p>\n |