Why ISPs seek alternatives to CGNAT
The IPv4 problem is real. Global reserves are depleted, and an increasing number of operators rely on CGNAT (Carrier-Grade NAT) to stretch their addresses. But CGNAT does not come for free. It introduces higher latency, fewer available ports, and headaches with geolocation services. This is why many ISPs are looking the other way.
The numbers speak for themselves. According to the regional Internet registries, APNIC and RIPE have virtually exhausted their IPv4 pools. And although IPv6 exists, its adoption does not reach 40% in many markets. So, transition solutions must be sought. Alternatives like Dual-Stack Lite (DS-Lite), Mapping of Address and Port (MAP), or Locator/ID Separation Protocol (LISP) promise scalability without so many headaches. Let’s take a closer look at them.
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Dual-Stack Lite (DS-Lite)
How it works
DS-Lite encapsulates IPv4 traffic within an IPv6 infrastructure. The ISP assigns a single IPv6 address to the subscriber, and IPv4 connectivity is resolved using a centralized NAT at the operator’s edge. The result: the customer does not need a public IPv4.
Pros and cons
- Pros: It deploys easily on existing CPEs with an integrated DS-Lite client. It reduces IPv4 consumption and supports IPv6 natively.
- Cons: It still relies on a centralized NAT device, which is a single point of failure. Port limitations are the same as with CGNAT.
For ISPs that have already invested in IPv6, DS-Lite is a pragmatic alternative. But beware: it does not eliminate the CGNAT bottleneck. It simply moves it elsewhere.
Mapping of Address and Port (MAP-T/E)
The shared infrastructure approach
MAP (including MAP-T and MAP-E) uses a stateless algorithm to assign ports to customers. Instead of a stateful NAT, each subscriber receives a fixed range of ports that maps to a shared IPv4 address. This reduces port collisions and eliminates the need for a massive NAT table.
MAP divides the IPv4 address into a prefix (shared by many) and a PSID (Port Set Identifier). Each customer uses only a subset of ports of a public IP, but the mapping is done locally by the CPE. The result is near-native performance with very low latency.
| Feature | CGNAT | MAP-T/E |
|---|---|---|
| Stateful firewall | Yes (heavy) | No (stateless) |
| Scalability | Moderate (port limit) | High (algorithmic) |
| Latency | Increases | Almost zero |
| CPE support | Wide | Requires MAP client |
Locator/ID Separation Protocol (LISP)
Rethinking the routing architecture
LISP separates the device identity (EID) from its location (RLOC). It allows ISPs to use a small group of globally routable IPv4 addresses while traffic travels over a mapping overlay. This alternative to CGNAT is ideal for multi-homing and traffic engineering.
With LISP, NAT disappears. End users have stable IP addresses (EIDs) that appear accessible, while the ISP’s edge routers translate them to RLOCs. The protocol is standardized (RFC 6830) and is used by large enterprises and some mobile operators. However, it requires a major network redesign.
Native transition to IPv6 (the ultimate goal)
The most definitive alternative to CGNAT is the full adoption of IPv6. By assigning IPv6 to each customer, ISPs can stop sharing IPv4 addresses. IPv6 offers a massive address space (340 undecillion addresses), and it eliminates NAT problems at the root. The problem is that running in dual-stack mode (IPv6 + IPv4) still requires some IPv4, and there is legacy content that only lives on IPv4.
For a smoother transition, there is 464XLAT (RFC 6877). It allows devices to connect to IPv4 services over an IPv6 network without CGNAT on the client side. It is used by many mobile operators (for example, T-Mobile USA) and works on almost all modern smartphones.
According to ISOC data, IPv6 traffic already accounts for more than 30% of global mobile traffic. ISPs that invest in IPv6 now will reduce the pressure from IPv4 depletion for years.
IPv4 address trading platforms
When technical transitions move slowly, ISPs need to obtain IPv4 addresses somehow. The IPv4 block market remains active, with prices varying according to subnet size and region. According to industry reports, a /24 block can cost more than $3,000. For large ISPs, IPv4 leasing is also common.
This is where trusted marketplaces like IP4 Market come into play. With verified sellers and competitive prices, IP4 Market helps ISPs get the addresses they need without the risks of peer-to-peer transfers. Whether it’s a /22 block for short-term capacity or a /16 for long-term growth, the platform ensures seamless RIR approvals.
- Verified seller identities and address ownership
- Competitive pricing with no hidden fees
- Long-term lease and purchase options
- Simple transfer process compliant with RIRs
Comparison of CGNAT alternatives
| Alternative | IPv4 consumption | Latency | Deployment effort | Ideal for |
|---|---|---|---|---|
| DS-Lite | Minimal (shared IPv4) | Medium | Low | ISPs with IPv6 already deployed |
| MAP-T/E | Low (shared ports) | Low | Medium | Large access networks |
| LISP | Minimal (identity) | Very low | High | Enterprises/mobile operators |
| IPv6 + 464XLAT | Very low (legacy IPv4) | Low | Medium | Fixed and mobile broadband |
| Address trading (IP4 Market) | Full IPv4 allocation | None | Low (administrative) | Short-term capacity needs |
How to choose the right path
The best alternative to CGNAT for your ISP depends on your infrastructure, customer base, and budget. If you already have IPv6 deployed, DS-Lite or MAP-T/E are cost-effective intermediate options. If what you need is to maintain IPv4 accessibility for legacy services, the IP4 Market leasing platform can cover the gaps.
- Audit your current IPv4 usage and traffic growth rate.
- Evaluate the capabilities of your CPEs (do they support MAP-T/E or 464XLAT?).
