HP VPN Firewall Appliances VPN Configuration Guide

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As shown in Figure 57, 6to4 network Site 1 communicates with IPv6 network Site 3 over a
6to4 tunnel. A static route must be configured on the border router (Device A) in the 6to4
network and the next-hop address must be the 6to4 address of the 6to4 relay router (Device C).
Device A forwards all packets destined for the IPv6 network over the 6to4 tunnel and Device
C then forwards them to the IPv6 network.
Figure 57 Principle of 6to4 tunneling and 6to4 relay
4. ISATAP tunneling
An ISATAP tunnel is a point-to-point automatic tunnel. It provides a solution to connect an IPv6 host
to an IPv6 network over an IPv4 network.
The destination addresses of IPv6 packets and the IPv6 addresses of tunnel interfaces are all
ISATAP addresses. The ISATAP address format is prefix(64bit):0:5EFE:ip-address. The 64-bit
prefix is a valid IPv6 unicast address prefix; ip-address is a 32-bit IPv4 address in the format of
abcd or abcd:efgh, which identifies the tunnel destination and does not need to be globally
unique.
ISATAP tunnels are mainly used for communication between IPv6 routers or between an IPv6 host
and an IPv6 router over an IPv4 network.
Figure 58 Principle of ISATAP tunneling
IPv4 over IPv4 tunneling
IPv4 over IPv4 tunneling (RFC 1853) enables isolated IPv4 networks to communicate with each other over
another IPv4 network. For example, an IPv4 over IPv4 tunnel can connect isolated private IPv4 networks
over a public IPv4 network.