Dual Stack Backbones
In this model, all routers in the backbone are dual-stack, capable of routing both IPv4 and IPv6 packets. The IPv4 protocol stack is used between IPv4 hosts, and the IPv6 protocol stack is used between IPv6 hosts. This deployment model works for organizations with a mixture of IPv4 and IPv6 applications. Figure 8-8 shows a network with a dual-stack backbone. All the WAN routers run both IPv4 and IPv6 routing protocols. The disadvantages are that the WAN routers require dual addressing, run two routing protocols, and might require additional CPU and memory resources. Another disadvantage is that IPv4-only and IPv6-only hosts cannot communicate with each other directly; dual-stack hosts or network translation is required (covered next) for IPv4 and IPv6 hosts to communicate.
Figure 8-8 Dual-Stack Backbone
Figure 8-8 Dual-Stack Backbone
Dual-Stack Hosts
Hosts require dual stacks (IPv4 and IPv6) to communicate with both IPv4 and IPv6 hosts. In this environment, host applications can communicate with both IPv4 and IPv6 stacks. When using dual stacks, a host uses DNS to determine which stack to use to reach a destination. If DNS returns an IPv6 (A6 record) address to the host, the host uses the IPv6 stack. If DNS returns an IPv4 (A record) address to the host, the host uses the IPv4 stack. Using dual stacks is the method recommended for campus and access networks during a transition to IPv6.
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