3Com MSR 50 Series Configuration Manual page 696

696 C 49: T
HAPTER UNNELING
C
ONFIGURATION
2 Automatic IPv4-compatible IPv6 tunnel
An automatic IPv4-compatible IPv6 tunnel is a point-to-multipoint link.
IPv4-compatible IPv6 addresses are adopted at both ends of such a tunnel. The
address format is 0:0:0:0:0:0:a.b.c.d/96, where a.b.c.d represents an embedded
IPv4 address. The tunnel destination is automatically determined by the embedded
IPv4 address, which makes it easy to create a tunnel for IPv6 over IPv4. However,
an automatic IPv4-compatible IPv6 tunnel must use IPv4-compatible IPv6
addresses and it is still dependent on IPv4 addresses. Therefore, automatic
IPv4-compatible IPv6 tunnels have limitations.
3 6to4 tunnel
Ordinary 6to4 tunnel
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An automatic 6to4 tunnel is a point-to-multipoint tunnel and is used to connect
multiple isolated IPv6 domains over an IPv4 network to remote IPv6 networks. The
embedded IPv4 address in an IPv6 address is used to automatically acquire the
destination of the tunnel. The automatic 6to4 tunnel adopts 6to4 addresses. The
address format is 2002:abcd:efgh:subnet number::interface ID/64, where
abcd:efgh represents the 32-bit source IPv4 address of the 6to4 tunnel, in
hexadecimal notation. For example, 1.1.1.1 can be represented by 0101:0101.
The tunnel destination is automatically determined by the embedded IPv4 address,
which makes it easy to create a 6to4 tunnel.
Since the 16-bit subnet number of the 64-bit address prefix in 6to4 addresses can
be customized and the first 48 bits in the address prefix are fixed by a permanent
value and the IPv4 address of the tunnel source or destination, it is possible that
IPv6 packets can be forwarded by the tunnel. A 6to4 tunnel interconnects IPv6
networks and overcomes the limitations of an automatic IPv4-compatible IPv6
tunnel.
6to4 relay
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A 6to4 tunnel can connect networks whose address prefix is 2002::/16. However,
IPv6 network addresses with the prefix such as 2001::/16 may also be used in IPv6
networks. In order for these addresses to be reachable, a 6to4 router must be used
as a gateway to forward packets to IPv6 networks. Such a router is called 6to4
relay router. As shown in
border routers in the 6to4 network and the next-hop address must be the 6to4
address of the 6to4 relay router. In this way, all packets destined for the IPv6
network will be forwarded to the 6to4 relay router, and then to the IPv6 network.
Thus, interworking between the 6to4 network (with the address prefix starting
with 2002) and the IPv6 network is realized.
Figure 206, a static route must be configured on the