Some weeks ago we installed critical patch updates (CPU) on a Solaris 10 system (internal system, a year of CPU to install, nothing in it affecting us or was considered a security risk, we decided to apply this one regardless to not fall behind too much). Afterwards we noticed that two zones are doing a lot of DNS requests. We noticed this already before the zones went into production and we configured a positive time to live in nscd.conf for “hosts”. Additionally we noticed a lot of DNS requests for IPv6 addresses (AAAA lookups), while absolutely no IPv6 address is configured in the zones (not even for localhost… and those are exclusive IP zones). Apparently with one of the patches in the CPU the behaviour changed regarding the caching, I am not sure if we had the AAAA lookups before.
Today I got some time to debug this. After adding caching of “ipnodes” in addition to “hosts” (and I configured a negative time to live for both at the same time), the DNS requests came down to a sane amount.
For the AAAA lookups I have not found a solution. By my reading of the documentation I would assume there are not IPv6 DNS lookups if there is not IPv6 address configured.