Figure 7-14 Cisco IOS Dual Stack
IPv4
IPv6
IPv4/IPv6
IPv6
Internet
IPv4
Internet
Transitioning to IPv6 285
You can accomplish this con?¬?guration on the same interface or on multiple interfaces.
Features of the dual-stack method are as follows:
?– A dual-stack node chooses which stack to use based on the destination address. A dualstack
node should prefer IPv6 when it is available. The dual-stack approach to IPv6
integration, in which nodes have both IPv4 and IPv6 stacks, will be one of the most
commonly used integration methods. Old IPv4-only applications continue to work as
before. New and modi?¬?ed applications take advantage of both IP layers.
?– A new application programming interface (API) is de?¬?ned to support both IPv4 and
IPv6 addresses and DNS requests. This new API replaces the gethostbyname and
gethostbyaddr calls. A converted application can use both IPv4 and IPv6. An
application can be converted to the new API while still using only IPv4.
?– Experience in porting IPv4 applications to IPv6 suggests that, for most applications,
there is a minimal change in some localized places inside the source code. This
technique is well known and has been applied in the past for other protocol transitions.
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