Unbound wont start in this config. (system tunables) pfsense 2.1.5
When increasing the kern.ipc.maxsockbuf to 167772016 then Unbound fails to start with this error:
php: rc.start_packages: The command '/usr/pbi/unbound-amd64/sbin/unbound-control start' returned exit code '1', the output was ' unbound[56404:0] error: bind: address already in use  unbound[56404:0] fatal error: could not open ports'
Anybody care to explain why since its the 16777216 is recommended on Freebsd when running 10gbe hardware.
Tunables recommended for FreeBSD in a server role often do not make sense for pfSense in a firewall role. The nature of connections and traffic are completely different.
Tunables shouldn't be added or changed unless the implications are properly understood for all of them. There isn't a "one size fits all" list of tunables to be applied. We set things by default that are good to have, and others may be tweaked but unless there is a reason for doing so, don't apply values that are "recommended" for other configurations.
That said, the error you see would likely also happen to Unbound on FreeBSD in the same configuration.