NTP recommedations

["Jennifer Fountain" <JFountain () rbinc com>]

I am currently looking into configuring my company's time servers.  My initial thoughts were setting up two or three in 
the dmz and configuring them to update their time on a regular basis (haven't defined regular yet) and then install two 
or three interal time servers that query these servers.  I currently have a web server, reverse proxy, ftp (blush 
embarrassed - going to be getting rid of THIS real soon), email, ids, and two dns servers in the dmz.  Someone has 
recommended to configure three of these servers (web, dns, and email) as a time server.  At first, I say - huh - no.  
That would mean opening up two ports on each box and having a new set of potential problems if i miss anying.  But I am 
not an expert so I head to google searches and you for guidance.  Could anyone tell me their configuration or recommend 
a "good" configuration for company time servers?  

Thank you
Jenn

P.S  If anyone is at SANS 2003, ping me if you are in track 3 :)