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IPv4/IPv6 coexistence and dual stack

Short answer

IPv4 and IPv6 coexist by operating simultaneously during transition. Dual stack means a host runs both protocol stacks, obtains an IPv4 and IPv6 address, and uses DNS (A or AAAA record) to select the version for communication.

'IPv4 and IPv6 coexist': what does this mean? Explain the dual stack approach with an appropriate figure.

Coexistence of IPv4 and IPv6

"IPv4 and IPv6 coexist" means that for many years both protocols operate side by side on the Internet, because IPv6 is not backward compatible and billions of IPv4 devices cannot be replaced at once. Networks, hosts and applications using either version must continue to communicate during the transition period.

Dual stack approach

In the dual stack method, a host or router has both an IPv4 stack and an IPv6 stack implemented on the same interface, and therefore has both an IPv4 address and an IPv6 address.

        Application (browser)
              |
        +-----+------+
        |  TCP / UDP |
        +--+------+--+
           |      |
        IPv4     IPv6
           +--+---+
        Ethernet / Wi-Fi

Working

  1. The application asks DNS for the destination. If DNS returns an AAAA record, the host uses IPv6; if only an A record is returned, it uses IPv4.
  2. The IPv4 packet or IPv6 packet is then built by the corresponding stack.
  3. Routers run both protocols and both routing protocols (e.g. OSPFv2 and OSPFv3), and forward each packet according to its version.
IPv4 host --- [dual stack router] --- IPv6 host
        dual-stack host talks to both

Advantages and limitations

  • Simple, no translation, full features of both protocols, gradual deployment.
  • Each device needs two addresses and two sets of configuration and security rules; memory and processing are higher; still needs IPv4 addresses, so the shortage remains.

✓ Answer checked by Claude Opus 5.5 (high effort)

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