nmap should automatically do a reverse dns lookup on an ip when you scan it, although there are easier ways to do it than using nmap.
If you're trying to scan a host using nmap and it gives you a message about the host not being up, try with -P0 (that's -P[zero]). nmap will try to ping a host to determine whether it's up or not before scanning so hosts blocking ping will exhibit this behaviour.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...