Technical data

B. Appendixes to optional packages
Long story short: The subnet must be made smaller. It has to become a /64 subnet for
auto-configuration to work properly. But that’s easy: the subnet mask has to be changed to
/64. If SixXS e.g. assigned the subnet 2001:db8:123::/48 then the subnet for fli4l is just
set to 2001:db8:123::/64. In detail this means that the /48 subnet is divided in 2
64 48
2
16
65536 sub-subnets. The first with the number zero is to be used with fli4l. You
have to remember that the short form 2001:db8:123:: really represents the long address
2001:db8:123:0:0:0:0:0. The first three numbers are the IPv6 provider’s globally unique
part of the subnet, the fourth number represents the selected sub-subnet “zero”,
4
and the last
four numbers are reserved for the host portion. This still gives a huge (sub-) subnet where up
to 2
64
18, 4 trillion hosts can be accommodated. Thanks to the IPv6 autoconfiguration you
will not have to bother about the actual addresses. And that’s good ...
Configuration
Back to the configuration! At first the variable IPV6_NET_N is set to “1” because exactly one local
IPv6 subnet has to be established. The IPv6 address of the /64 subnet including the subnet
mask goes to the variable IPV6_NET_1. But that’s not completely right: here the IPv6 address
of the router within that subnet is to be set, but without the subnet prefix that is associated
with the tunnel. In fact this is configured somewhere else: in the tunnel configuration. There
the variable IPV6_TUNNEL_1_PREFIX has to be set to the requested subnet prefix.
Example: Having received the /48er-IPv6-subnet 2001:db8:123::/48 from SixXS, chosen
it’s subnet with the number ‘456’ to be used as a /64 sub-subnet and finally determined that
the router within that subnet should get the address of “1”, we get the following configuration:
IPV6_NET_N='1'
IPV6_NET_1='0:0:0:456::1/64' # IPv6-address of the routers (without
# subnet-prefix) + subnet mask
IPV6_TUNNEL_1_PREFIX='2001:db8:123::/48' # /48-subnet-prefix
It should be noted that the first three zeros in IPV6_NET_1 hold the place for the /48-subnet-
prefix associated with the tunnel. Together with the /48 subnet prefix assigned by the tunnel
provider this results in the /64-Subnetz 2001:db8:123:456::/64 and the IPv6 router address
2001:db8:123:456::1.
Now we need the name of the network interface to which this subnet has to be bound. Each
subnet is bound to exactly one network interface. If only one configured network card is present
in the router the name of the network interface is typically “eth0” for wired or “wlan0” for
wireless adapters. If in doubt have a look at IP_NET_1_DEV (“IP” without “6”) and copy the
content:
IPV6_NET_1_DEV='eth0' # Network interface for this IPv6-subnet
Finally we just need to let IPv6 autoconfiguration do the rest:
IPV6_NET_1_ADVERTISE='yes' # /64-subnet-prefixaund default-route per RA
IPV6_NET_1_ADVERTISE_DNS='yes' # DNS-server per RA (needs
# DNS_SUPPORT_IPV6='yes'!)
IPV6_NET_1_DHCP='yes' # Domain-name and DNS-server per DHCPv6
# (needs DNS_SUPPORT_IPV6='yes')
4
Of course you can have another sub-subnet!
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