3Com Switch 8800 Advanced Software V5 Configuration Guide

378 CHAPTER 33: TUNNELING CONFIGURATION
Figure 113 6to4 tunnel
4 ISATAP tunnel
With the application of the IPv6 technique, there will be more and more IPv6 hosts
in the existing IPv4 network. The ISATAP tunneling technique provides a
satisfactory solution for IPv6 application. An ISATAP tunnel is a point-to-point
automatic tunnel. The destination of a tunnel can automatically be acquired from
the embedded IPv4 address in the destination address of an IPv6 packet. When an
ISATAP tunnel is used, the destination address of an IPv6 packet and the IPv6
address of a tunnel interface both adopt special addresses: ISATAP addresses. The
ISATAP address format is prefix (64bit):0:5EFE:ip-address. The ip-address is in the
form of a.b.c.d or abcd:efgh, where abcd:efgh represents a 32-bit source IPv4
address. Through the embedded IPv4 address, an ISATAP tunnel can automatically
be created to transfer IPv6 packets. The ISATAP tunnel is mainly used for
connection between IPv6 host and IPv6 router.
Figure 114 ISATAP tunnel
5 GRE tunnel
IPv6 packets can be carried over GRE tunnels to pass through the IPv4 network by
using standard GRE protocol to encapsulate them. Like the IPv6 manually
configured tunnel, a GRE tunnel is a point-to-point link, too. Each link is a separate
tunnel. The GRE tunnel is mainly used for stable connections requiring regular
secure communication between two border routers or between a host and a
border router. For related configurations, refer to
“GRE Configuration” on page
405.
Expedite termination
With expedite termination disabled, a tunnel packet arriving at the destination
node is first forwarded to the CPU for processing, then the outer IPv4 header is
removed, and finally the decapsulated original packet is forwarded. With expedite
termination enabled, the tunnel packet is unnecessarily sent to the CPU for
processing, but is directly processed as IPv6 packets.
IPv4 network
6to4 network
Site 1
IPv4 network
Site 3
6to4 network
Site 2
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Router A
Router B
Router C
6to4 router
6to4 relay
6to4 router
IPv6 network
IPv4 network
ISATAP tunnel
IPv6 host
IPv4/IPv6 host
ISATAP router
IPv4 address:
2.1.1.1/24
IPv6 address:
FE80::5EFE:0201:0101
3FFE::5EFE:0201:0101