Bind 9 Administrator Reference Manual

Chapter 4. Advanced Concepts
4.8.2. Address Lookups Using A6 Records
The A6 record is more flexible than the AAAA record, and is therefore more complicated. The A6 record
can be used to form a chain of A6 records, each specifying part of the IPv6 address. It can also be used to
specify the entire record as well. For example, this record supplies the same data as the AAAA record in
the previous example:
$ORIGIN example.com.
host 3600 IN A6 0 3ffe:8050:201:1860:42::1
4.8.2.1. A6 Chains
A6 records are designed to allow network renumbering. This works when an A6 record only specifies the
part of the address space the domain owner controls. For example, a host may be at a company named
"company." It has two ISPs which provide IPv6 address space for it. These two ISPs fully specify the
IPv6 prefix they supply.
In the company’s address space:
$ORIGIN example.com.
host 3600 IN A6 64 0:0:0:0:42::1 company.example1.net.
host 3600 IN A6 64 0:0:0:0:42::1 company.example2.net.
ISP1 will use:
$ORIGIN example1.net.
company 3600 IN A6 0 3ffe:8050:201:1860::
ISP2 will use:
$ORIGIN example2.net.
company 3600 IN A6 0 1234:5678:90ab:fffa::
When host.example.com is looked up, the resolver (in the resolver daemon or caching name server)
will find two partial A6 records, and will use the additional name to find the remainder of the data.
4.8.2.2. A6 Records for DNS Servers
When an A6 record specifies the address of a name server, it should use the full address rather than
specifying a partial address. For example:
$ORIGIN example.com.
@ 14400 IN NS ns0
14400 IN NS ns1
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