reverse dns works for an ip to a domain. It may not allow you to look up an ip for multiple sites as you mentioned. You need to choose a lookup domain and contact your host(or the DC) to set that up for you. It will need to be setup on the main DNS of your DC, so that other ISP's can identify the ip and reverse lookup.
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Reverse dns is not set default for a IP by default. We have to contact NOC for setting up this. There are certain emails providers that insists for reverse dns for an IP to relay mail thrpough the servers. Eg AOL.
Codeguru is correct, if you have not made arrangements with your ISP to delegate the in-addr.arpa (rDNS) records to your nameservers, then you will have to have the ISP make the changes (or if they are willing, have them delegate it to your nameservers).
If they delegate to yours, then you will have to create and maintain the zz.xx.yy.ww.in-addr.arpa zone file for your IP(s).