Unbound is a validating, recursive, and caching DNS resolver.

The C implementation of Unbound is developed and maintained by NLnet
Labs. It is based on ideas and algorithms taken from a java prototype
developed by Verisign labs, Nominet, Kirei and ep.net.

Unbound is designed as a set of modular components, so that also
DNSSEC (secure DNS) validation and stub-resolvers (that do not run
as a server, but are linked into an application) are easily possible.

1. build dependencies:
   1. /proc
   2. libssl-devel
   3. flex
   4. gcc-c++
   5. pkgconfig(libsystemd)
   6. libevent-devel
   7. libexpat-devel