BIND, installing
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Installing BIND is fairly straightforward; the latest version is 9.3.1 and it's in ports:
# cd /usr/ports/dns/bind9 # make install clean
and you're pretty much done.
Wait, I thought you said we were done
Well, you're done if you want a standard install. If you want a really secure DNS server, you're probably going to want to install BIND in a chroot jail. It's a pain, but it means that even if your server gets compromised, the rest of the box isn't at risk.