Bind 9 Administrator Reference Manual

Appendix A. Appendices
FP TLA
ID
RES NLA ID SLA ID Interface ID
<—— Public Topology ——>
<-Site Topology->
<—— Interface Identifier ——>
Where
FP = Format Prefix (001)
TLA ID = Top-Level Aggregation Identifier
RES = Reserved for future use
NLA ID = Next-Level Aggregation Identifier
SLA ID = Site-Level Aggregation Identifier
INTERFACE ID = Interface Identifier
The Public Topology is provided by the upstream provider or ISP, and (roughly) corresponds to the IPv4
network section of the address range. The Site Topology is where you can subnet this space, much the
same as subnetting an IPv4 /16 network into /24 subnets. The Interface Identifier is the address of an
individual interface on a given network. (With IPv6, addresses belong to interfaces rather than machines.)
The subnetting capability of IPv6 is much more flexible than that of IPv4: subnetting can now be carried
out on bit boundaries, in much the same way as Classless InterDomain Routing (CIDR).
The internal structure of the Public Topology for an A6 global unicast address consists of:
3 13 8 24
FP TLA ID RES NLA ID
A 3 bit FP (Format Prefix) of 001 indicates this is a global Unicast address. FP lengths for other types of
addresses may vary.
13 TLA (Top Level Aggregator) bits give the prefix of your top-level IP backbone carrier.
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