Information Technology Reference
In-Depth Information
DSTM proposes the use of a dual stack that uses IPv4 addresses only when needed and
the use of IPv4 over IPv6 tunneling to reach a destination IPv4 address. It is used when
there is an IPv6-only backbone but an application needs to reach an IPv4 address.
RFC 2766 describes NAT-PT, which provides translation between IPv6 and IPv4 hosts.
NAT-PT operates similarly to the NAT mechanisms to translate IP v4 private addresses to
public address space. NAT-PT binds addresses in the IPv6 network to addresses in the
IPv4 network and vice versa. Figure 9-12 shows a network using NAT-PT. RFC 4699 is a
recent Informational RFC that recommends that NAT-PT be placed into historical status
and recommends against its use (although the protocol is still supported in IOS).
NAT-PT
IPv6 Site A
IPv4 Site B
Figure 9-12
Network Address Translation-Protocol Translation
Cisco also introduces the Cisco 6PE for Multiprotocol Label Switching (MPLS) service
providers. Cisco 6PE allows IPv6 islands to communicate over an MPLS/IPv4 core net-
work using MPLS label-switched paths (LSP). The Cisco 6PE routers are dual stack. The
method relies on BGP extensions in the IPv4 6PE routers to exchange IPv6 reachability in-
for mat ion, along w ith an MPL S label for each IP v6 addre s s prefix announced.
IPv6 Deployment Models
Deployment of IPv6 can be done in one of the following models:
Dual-stack model (IPv4 and IPv6 coexist on hosts and network)
■
Key
To p i c
Hybrid model (combination of ISATAP or manually configured tunnels and dual-
stack mechanisms)
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Service block model (combination of ISATAP and manually configured tunnels and
dual-stack mechanisms)
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Dual-Stack Model
In the dual-stack model, both devices and the network routers and switches all run both
IPv4 and IPv6 protocol stacks. The applications on the devices decide which stack to use
to communicate with destination hosts. Or DNS is used to decide which stack to use. A
DNS AAAA RR return uses IPv6, and a DNS A RR return uses IPv4. Because most ma-
ture operating systems are now supporting IPv6, this is the preferred technique for transi-
tion to IPv6. Figure 9-13 shows a dual-stack network where both protocols reside. Older
IPv4 sites that have not migrated to the dual-stack model can communicate
the network with other IPv4 devices.
