As government agencies worldwide face increasing mandates to modernize digital infrastructure, the transition from legacy dual-stack environments to IPv6-only networks has become a strategic priority. However, the path to a "pure" IPv6 environment is often obstructed by the persistent reality of IPv4-only hosts and legacy applications.

Cisco IT recently completed a successful Proof of Concept (POC) at our Bangalore campus, demonstrating how agencies can maintain seamless connectivity to the IPv4 world while operating on an IPv6-only foundation. By leveraging NAT64 and DNS64 technologies, we have developed a scalable, redundant architecture that serves as a roadmap for public sector digital transformation.

The Core Challenge: Interoperability in a Hybrid World

The primary obstacle in any IPv6 migration is that the source and destination must both be IPv6-enabled to communicate natively. In a government context, many external service providers, legacy internal databases, and public-facing websites remain IPv4-only. To bridge this gap, a translation mechanism is required to parse IPv6 headers and map them accurately into IPv4 formats without disrupting the user experience.

The Translation Engine: DNS64 and NAT64

Our deployment utilizes a two-part system to handle traffic between IPv6-only clients and IPv4-only destinations:

1. DNS64: When a client requests a domain that only has an IPv4 address (A record), the DNS64 server (running BIND9 on RHEL) synthesizes a temporary IPv6 address. It does this by prepending a 96-bit prefix to the 32-bit IPv4 address.
2. NAT64: Once the client sends traffic to this synthesized address, the NAT64 gateway (utilizing Cisco Catalyst 8500 or ASR1000 series routers) translates the packet into IPv4 for the destination and handles the return traffic back to IPv6.

Strategic Implementation: Stateful vs. Stateless

Cisco IT's deployment highlights two distinct translation methods tailored to specific agency needs:

• Stateful NAT64: This is used for general campus data traffic. It allows many IPv6 clients to share a pool of IPv4 addresses, maximizing efficiency for standard web browsing and application access.
• Stateless NAT64: For specific use cases like security cameras or IoT devices, we implemented stateless translation. This provides a deterministic, one-to-one mapping between IPv4 and IPv6 addresses. This is particularly valuable for government facilities where the Video Management System (VMS) is IPv4-only but must reach specific, identifiable IPv6 cameras.

Ensuring Mission-Critical Resilience

For government operations, downtime is not an option. Our architecture incorporates Inter-chassis Redundancy. By configuring NAT64 gateways in an Active/Standby pair, translation states are synchronized in real-time. If the primary gateway fails, the standby takes over immediately, ensuring that connectivity to critical IPv4 resources remains uninterrupted.

A Proven Path Forward

The transition to IPv6 is no longer a distant goal but a current requirement for modern, secure, and scalable government operations. By implementing a combination of DNS64 and NAT64, Cisco IT has proven that agencies can adopt an IPv6-only posture today without sacrificing access to the legacy systems of yesterday. This "Cisco-on-Cisco" approach provides a validated, high-performance framework for any organization ready to lead in the IPv6 era.

Next Steps

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