Bind 9 Administrator Reference Manual

Chapter 6. BIND 9 Configuration Reference
for forward lookups and "nibble labels" in the ip6.int domain for reverse lookups, but do not support
RFC2874-style lookups (using A6 records and binary labels in the ip6.arpa domain).
For those who wish to continue to use such stub resolvers rather than switching to the BIND 9
lightweight resolver, BIND 9 provides a way to automatically convert RFC1886-style lookups into
RFC2874-style lookups and return the results as "synthetic" AAAA and PTR records.
This feature is disabled by default and can be enabled on a per-client basis by adding a
allow-v6-synthesis { address_match_list }; clause to the options or view statement. When it is
enabled, recursive AAAA queries cause the server to first try an A6 lookup and if that fails, an AAAA
lookups. No matter which one succeeds, the results are returned as a set of synthetic AAAA records.
Similarly, recursive PTR queries in ip6.int will cause a lookup in ip6.arpa using binary labels, and
if that fails, another lookup in ip6.int. The results are returned as a synthetic PTR record in ip6.int.
The synthetic records have a TTL of zero. DNSSEC validation of synthetic responses is not currently
supported; therefore responses containing synthetic RRs will not have the AD flag set.
Note: allow-v6-synthesis is only performed for clients that are supplied recursive service.
6.2.14.14. Tuning
lame-ttl
Sets the number of seconds to cache a lame server indication. 0 disables caching. (This is NOT
recommended.) Default is 600 (10 minutes). Maximum value is 1800 (30 minutes).
max-ncache-ttl
To reduce network traffic and increase performance the server stores negative answers.
max-ncache-ttl is used to set a maximum retention time for these answers in the server in seconds.
The default max-ncache-ttl is 10800 seconds (3 hours). max-ncache-ttl cannot exceed 7 days and
will be silently truncated to 7 days if set to a greater value.
max-cache-ttl
max-cache-ttl sets the maximum time for which the server will cache ordinary (positive) answers.
The default is one week (7 days).
min-roots
The minimum number of root servers that is required for a request for the root servers to be
accepted. Default is 2.
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