Firewalls That Check DNS Entries?

Stonefish asks: "I was wondering if there is a firewall or packet filter that only allows traffic from the internal network to external networks if the host has an entry in DNS. Currently the network that I administer uses a bootptab file with MAC addresses. I would like to get to the stage where DHCP gets a request from a valid MAC address, adds the entries to DNS and the firewall checks outgoing packets for a valid DNS entry, it's simple but not foolproof. Currently in most organisations there is either an all-or-nothing approach to networking. As newer DNS implimentations are incorporating public keys other methods that incorporate a more secure DNS->firewall interaction are possible and equally obvious."