Information Technology Reference
In-Depth Information
Figure 9-11 shows a network using IPv4 tunnels. Site A and Site B both have IPv4 and
IPv6 networks. The IPv6 networks are connected using an IPv4 tunnel in the WAN.
IPv6 Site A
IPv6 Site B
IPv4 WAN
IPv4 Tunnel
IPv4 Site A
IPv4 Site B
Figure 9-11
IPv6 over IPv4 Tunnels
6over4 is another tunnel method that requires an IPv4 multicast-enabled network. IPv6
multicast packets get encapsulated into IPv4 multicast packets to communicate with other
6over4 hosts. 6over4 is of limited practical use.
Another method to tunnel IPv6 over IPv4 is the Intra-Site Automatic Tunnel Addressing
Protocol (ISATAP). With ISATAP, a tunnel is created between dual-stack hosts or routers
to transmit IPv6 packets over an IPv4 network. Unlike 6over4 mechanism, ISATAP does
not require the IPv4 to be multicast enabled.
With ISATAP the link-local address is generated by concatenating
FE80:0000:0000:0000:0000:5EFE: with the IPv4 address expressed in hexadecimal. For
example, with IPv4 192.168.10.10 the link-local address is
FE80:0000:0000:0000:0000:5EFE: C0A8:0A0A. ISATAP also requires the use of a
routable address (for example, a global unicast IPv6 address that uses the same 0000:5EFE
IANA reserved value for the interface ID along with the 32-bit IPv4 embedded address).
Protocol Translation Mechanisms
One of the mechanisms for an IPv6-only host to communicate with an IPv4-only host
without using dual stacks is protocol translation. Translation is basically an extension to
IPv4 NAT techniques. Some techniques are
Application layer gateways (ALG):
These use dual stacks and allow one host on
the IPv4 domain to communicate with the host on the IPv6 domain.
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Application programming interfaces (API):
An API module intercepts IP traffic
through an API and coverts it for the IPv6 counterpart.
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Translation techniques:
(DSTM).
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