
IPv6 Overview
118428-A Rev. A 1-23
2. Router C encapsulates the IPv6 packet in an IPv4 header.
The source address in the IPv4 header is the IPv4 address of the local tunnel
interface on router C. The destination address is the IPv4 address of the
remote tunnel interface on router D.
3. Using the IPv4 header, intermediate IPv4 routers in Region 2 forward the
encapsulated packet through the IPv4 region to router D.
4. Router D decapsulates the packet (removing the IPv4 header) and forwards
the original IPv6 packet to router F.
After you have configured the IPv4 interfaces on the end point routers, the tunnel
becomes a permanent point-to-point link in the IPv6 topology.
Automatic IPv4 Tunnel
An automatic tunnel is a mechanism for forwarding unicast IPv6 packets that use
the IPv4-compatible address format. All routers in IPv6 regions that use automatic
tunneling must run both IPv6 and IPv4.
IPv6 creates the tunnel dynamically as needed for the purpose of forwarding an
IPv6 packet through multiple IPv4 and IPv4/IPv6 routers.
In F
igure 1-5, for example, a user connected to router B in Region 1 wants to send
an IPv6 packet to a user on router J in Region 3.
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