Information Technology Reference
In-Depth Information
over the IPv4 WAN. The advantage of this method is that you do not need separate cir-
cuits to connect the IPv6 networks. A disadvantage of this method is the increased proto-
col overhead of the encapsulated IPv6 headers. Tunnels are created manually,
semiautomatically, or automatically.
Application
TCP
UDP
IPv4
IPv6
0x0800
0x86DD
Ethernet
Figure 9-10
Dual-Stack Mechanism
For manually config ured (static config uration) tunnels, the tunnels are config ured w ith
IPv4 and IPv6 addresses for tunnel source and destination. Tunnels can be built between
border routers or between routers and hosts.
In semiautomatic configured tunnels, a tunnel broker is used. The tunnel broker is a server
on the IPv4 network that receives requests from dual-stack clients and builds a tunnel on
the tunnel router and associates it with the client.
Automatic tunnel mechanisms are
IPv4 compatible
■
6to4
■
6over4
■
ISATAP
■
IPv4-compatible tunnels use IPv4-compatible addresses. This mechanism does not scale,
and IP-compatible addresses have been deprecated, so this mechanism is appropriate only
for te st ing.
RFC 3056 specifies the 6to4 method for transition by assigning an interim unique IPv6
prefix. 2002::/16 is the assigned range for 6to4. Each 6to4 site uses a /48 prefix that is
concatenated with 2002. The border router extracts the IPv4 address that is embedded in
for wards it to the IP v6 de st inat ion.
