Technical data
B. Appendixes to optional packages
established fully by SixXS yet. In the second case you should wait for some time because the
configuration on the PoPs may last a few hours. If you double-checked the configuration and
discovered no mistakes, and some time has elapsed without the tunnel working, you should
contact SixXS by e-mail and describe the problem in detail.
B.11.3. Configuration Of The Subnet
Preparations
If the tunnel is working you made the first major step. But you have not yet finished. For now
only the router has the ability to send and receive packets to and from the IPv6 internet. But
the hosts in the local net can’t do this by now. An IPv6 subnet has to be configured to which
the local hosts are bound.
Here a small but significant difference to the configuration of an IPv4 network is to be
noticed: Because of the address shortage usually only one host is connected directly to the
internet. The other hosts on the local network receive only internal network IP addresses
that are not routed to the outside. These are in the ranges 192.168.*.*, 172.16.*.* to
172.31.*.*, and 10.*.*.*, depending on the size of the subnet.
2
With IPv6 we get far enough IP addresses thus eliminating the need to use internal network
addresses. Due to the global nature of local subnets it must be assured that the addresses of
local hosts do not collide with other addresses on the Internet. Therefore a subnet of the IPv6
Provider has to be allocated in order to avoid such collisions.
SixXS does this with the menu item “Request subnet”. Here you mainly have to specify
the tunnel to be used. This is easy because only one tunnel has been configured so far. After
submitting the form via “Place request for new subnet” you will, after some time, obtain the
following information by e-mail:
1. IPv6-address and subnet mask of the subnet (“Subnet IPv6”)
2. IPv6-address of the routers in the tunnel to where the subnet will be routed by SixXS
(“Routed to”)
3. IPv4-address of the router (“Your IPv4”)
3
This data is sufficient for configuring an own IPv6 subnet with fli4l. One more thing must
be known: The assigned subnet is usually very large. SixXS usually allocates /48-subnets,
i.e. within the 128-bit IPv6 address the proportion of the network prefix is 48 bits and the
proportion that is available for addressing of hosts is 128 - 48 = 80 bits. Such a large subnet
has two major drawbacks. The first disadvantage is the sheer size: this network can address
2
80
1209 trillion hosts. It appears inadvisable to use this without structuring the host portion
of the address. The second drawback is more serious: within such a large subnet the so-called
IPv6-autoconfiguration does not work. This is a process in which the IPv6 host receives the
subnet prefix on defined protocols and derives its IPv6 address from the MAC address of its
network adapter. The MAC address consists of six bytes. Using the standard EUI-64 you can
stretch it to eight bytes. This corresponds to 64 bits in the end. For 80-bit simply not enough
information is available on the host.
2
see RFC 1918(http://tools.ietf.org/html/rfc1918) for details
3
in case that the router gets its IPv4-address dynamically this will specifiy “heartbeat”
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