6To4 Tunnels Operation And Configuration Summary - Allied Telesis SwitchBlade x908 Series Software Reference Manual

When a switch is required to deliver packets, via a tunnel interface, to IPv6 addresses in the
range 2002:<ipv4-address>::/48, the switch knows that the IPv4 address to which
the switch must deliver that packet is given by the 17th through 48th bits of the IPv6
destination address. So, the encapsulation process extracts those bits from the IPv6 destination
address, and uses them as the IPv4 destination address in the encapsulating header.
For example, if 212.149.1.1 is the IPv4 address of a tunnel endpoint, then the IPv6
subnets in the range 2002:d495:101::/48 are automatically known to be reachable via
that tunnel endpoint. If another tunnel endpoint has an IPv6 packet to deliver to
2002:d495:101:6::04:8d, via the tunnel, then that switch will encapsulate the packet in
an IPv4 header with a destination address of 212.149.1.1
The corollary to this is the requirement that , to be reachable from other 6to4 networks, the
IPv6 VLAN interfaces on the IPv6 side a tunneling switch will need to be configured with IPv6
addresses that are subnetted from the 2002:<ipv4-address>::/48 address.
For example, 2002:<ipv4-address>:1::/64, 2002:<ipv4-address>:2::/
64, 2002:<ipv4-address>:3::/64, etc.
Note:

6to4 tunnels operation and configuration summary

1.
2.
3.
4.
C613-50007-01 REV B
2002:<ipv4-address>::/64
the automatically configured tunnel address.
When an IPv4 address is designated as the source address of a tunnel, that tunnel interface
is automatically given the IPv6 address
The switch does not automatically create any IPv6 routes via that tunnel interface, so you
do need to explicitly create a route to direct traffic over the tunnel interface.
Typically, you will create a route to
occasions, though, when you want to just create some more restricted routes, within the
range, over the tunnel interface.
2002::/16
Once routes have been created that direct traffic over the tunnel interface, it is not
necessary to specify nexthop addresses for the individual remote IPv6 subnets that are
reachable via the tunnel. The switch will automatically know the IPv4 nexthop via which to
reach any IPv6 subnet in the range 2002:<ipv4-address>::/48.
The only IPv6 addresses that can be routed to via the 6to4 tunnels on switches running
TM
AlliedWare Plus version 5.3.1 are IPv6 addresses of the form:
2002:<valid-IPv4-unicast-address>:xx:xx:xx:xx:xx
Software Reference for SwitchBlade® x908, x900 and x600 Series Switches
TM
AlliedWare Plus Operating System - Software Version 5.3.1
cannot be used here, because it conflicts with
2002:<ipv4-address>::1/128
via the tunnel interface. There might be
2002::/16
IPv6to4 Tunneling Configuration
26.3