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Chapter 26. Tunnel | 414
26
26. Tunnel
There are two methods for Pv6 sites to communicate with each other over the IPv4 network: 6in4
tunnel and 6to4 tunnel. The 6in4 tunnel encapsulates IPv6 traffic over an explicitly configured
IPv4 destination or end port of the tunnel with the IP protocol number set to 41. The 6to4 tunnel
IPv6 prefix is constructed by prepending 2002 (hex) to the global IPv4 address. For example, if
the IPv4 address is 4.4.4.1, the tunnel IPv6 prefix would be 2002:404:401::/16.
The 6to4 tunnels are automatically formed IPv4 tunnels carrying IPv6 traffic. The automatic
tunnel’
s IPv4 destination address is derived from the 6to4 IPv6 address of the tunnel’s nexthop.
It supports the functionality of a 6to4 border router that connects a 6to4 site to a 6to4 domain. It
sends/receives tunneled traffic from routers in a 6to4 domain that includes other 6to4 border
routers and 6to4 relay routers. The example creates a 6in4 tunnel between GSM7328S_1 and
GSM7328S_2. The tunnel carries IPv6 packets over IPv4 packets.
IPv4 Network
GSM7328S_1 GSM7328S_2
1/0/1 1/0/13
Figure 44. 6in4 tuennel between two switches