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What is 464XLAT?

464XLAT is a critical IPv6 transition mechanism that enables IPv4 applications to work seamlessly on IPv6-only networks. Standardized in RFC 6877 (2013), this technology has become the backbone of modern mobile networks, allowing carriers like T-Mobile US, Verizon Wireless, and Telstra to deploy IPv6-only infrastructure while maintaining complete IPv4 compatibility.

The Problem: IPv4 Applications on IPv6-Only Networks

As IPv4 address exhaustion forces network operators to transition to IPv6, a significant challenge emerges: millions of applications and services still require IPv4 connectivity. Early transition mechanisms like NAT64/DNS64 solved many problems but had critical limitations:

Popular mobile applications like Skype, WhatsApp, and many gaming apps fell into these problematic categories. Network operators needed a more comprehensive solution—and 464XLAT emerged as the answer.

464XLAT Architecture: Two-Stage Translation

The name "464XLAT" describes its operation: IPv4 → IPv6 → IPv4 with translation (XLAT) happening at both ends. The architecture combines stateless translation at the customer side with stateful translation at the provider side.

CLAT: Customer-side Translator

CLAT (Customer-side transLATor) operates on the user's device or CPE (Customer Premises Equipment). It performs stateless IPv4-to-IPv6 translation according to RFC 6145:

Key functions:

Implementation locations:

The beauty of CLAT is that applications see a normal IPv4 interface—they have no idea they're running on an IPv6-only network.

PLAT: Provider-side Translator

PLAT (Provider-side transLATor) runs in the service provider's network core. It performs stateful NAT64 translation according to RFC 6146:

Key functions:

PLAT is essentially carrier-grade NAT64 with specific optimizations for 464XLAT traffic.

How They Work Together

[IPv4 App] → [CLAT: 192.0.0.1 → 2001:db8::c000:1] →
    [IPv6-Only Network] →
    [PLAT: 2001:db8::c000:1 → 203.0.113.5] →
    [IPv4 Internet: 8.8.8.8]
  1. Application layer: App thinks it's sending IPv4 to 8.8.8.8
  2. CLAT translation: Translates source 192.0.0.1 and destination 8.8.8.8 into IPv6 format
  3. IPv6 transport: Packet travels through IPv6-only mobile/ISP network
  4. PLAT translation: Converts back to IPv4, applying NAT to share public IPv4 addresses
  5. IPv4 Internet: Packet reaches destination as normal IPv4 traffic

The round-trip works in reverse, with responses flowing back through both translators transparently.

Mobile Carrier Deployments: Real-World Success

T-Mobile US: Leading the Way

T-Mobile US was one of the first major carriers to deploy 464XLAT at scale, launching IPv6-only service in 2013:

T-Mobile's deployment solved critical application issues—Skype, WhatsApp, and other non-DNS-based apps that failed with NAT64/DNS64 alone worked perfectly with 464XLAT.

Verizon Wireless: Simplifying Network Architecture

Verizon deployed IPv6 proactively, even with sufficient IPv4 addresses, driven by operational complexity:

Telstra: IPv6-Only Mobile in 2020

Australian carrier Telstra completed a five-year IPv6 transition plan:

Other Major Deployments

Android Implementation: Native CLAT Support

Android has been the driving force behind 464XLAT adoption in mobile:

Android 4.3 (July 2013): Native CLAT

For more information on configuring IPv6 on mobile devices, see How to Configure IPv6 on Android and iOS Devices.

Configuration and Operation

When connected to an IPv6-only APN:

  1. Android detects absence of IPv4 address
  2. Discovers PLAT64 prefix via DNS64 or network hints
  3. Activates CLAT, creating virtual clat4 interface
  4. Assigns private IPv4 address (typically 192.0.0.4)
  5. Applications bind to IPv4 as normal
  6. All traffic translated transparently through IPv6 network

Developer Impact: Zero

From an application developer's perspective, 464XLAT is completely invisible:

This transparency is 464XLAT's greatest strength—it enables IPv6 transition without requiring app updates.

Comparison with Other Transition Mechanisms

464XLAT vs NAT64/DNS64

Feature NAT64/DNS64 464XLAT
DNS-based apps ✓ Works ✓ Works
IPv4 literals ✗ Fails ✓ Works
IPv4 socket binding ✗ Fails ✓ Works
Non-DNS protocols ✗ Fails ✓ Works
Client modifications None required CLAT required
Application visibility IPv6-only network Appears as dual-stack
Deployment complexity Simple Moderate

Verdict: 464XLAT is a strict superset of NAT64/DNS64 functionality. It solves all the same problems while adding support for IPv4 literals and direct socket binding.

464XLAT vs DS-Lite (Dual-Stack Lite)

Feature DS-Lite 464XLAT
IPv4 tunnel IPv4-in-IPv6 encapsulation Stateless translation
Network layer Requires IPv4 stack IPv6-only
MTU overhead Yes (encapsulation) No (translation)
Native IPv6 Yes Yes
IPv4 addressing Private IPv4 to device Virtual IPv4 interface
Use case Fixed broadband Mobile networks

Verdict: DS-Lite maintains IPv4 infrastructure via tunneling; 464XLAT achieves true IPv6-only operation with translation.

464XLAT vs Dual Stack

Feature Dual Stack 464XLAT
IPv4 addresses Required for every device Only at PLAT (shared)
IPv6 addresses Required Required
Scalability Limited by IPv4 exhaustion Highly scalable
Complexity Must operate two networks IPv6-only core
Future-proof No Yes
Cost Higher (dual infrastructure) Lower (single network)

Verdict: Dual stack is ideal during transition but unsustainable long-term. 464XLAT provides the same user experience while eliminating IPv4 infrastructure requirements.

Technical Benefits for Mobile Networks

Address Conservation

Network Simplification

Performance Optimization

Future-Proofing

Deployment Considerations

Network Requirements

  1. IPv6-only core network: Full IPv6 connectivity from device to PLAT
  2. PLAT deployment: Carrier-grade NAT64 infrastructure
  3. DNS64: Synthesizes AAAA records for IPv4-only destinations
  4. Well-Known Prefix: Use 64:ff9b::/96 or custom prefix for PLAT

Device Requirements

  1. CLAT support: Android 4.3+, iOS 9.2+, Windows 11, Linux
  2. IPv6 stack: Full IPv6 networking implementation
  3. APN configuration: IPv6-only APN settings

Transition Strategy

Phase 1: Enable IPv6

Phase 2: Deploy 464XLAT

Phase 3: IPv6-Only

Testing Your 464XLAT Connection

Want to know if your mobile device is using 464XLAT? Visit test-ipv6.run to run comprehensive connectivity tests:

Key indicators of 464XLAT:

The site will detect your network configuration and show whether you're on native dual-stack or using transition mechanisms like 464XLAT.

Conclusion: The Mobile Future is 464XLAT

464XLAT has emerged as the definitive solution for IPv6 transition in mobile networks. By combining customer-side stateless translation with provider-side stateful NAT64, it delivers:

Major carriers have validated this approach—T-Mobile US, Verizon, Telstra, and others have successfully deployed IPv6-only mobile networks using 464XLAT, achieving IPv6 deployment rates above 80% while maintaining seamless IPv4 service.

As the Internet continues its inevitable transition to IPv6, 464XLAT provides the bridge that makes migration practical, scalable, and invisible to end users. It's not just a transition mechanism—it's the architecture that makes IPv6-only mobile networks viable today.

Last updated: 2025-10-20

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