Multiple PTR Records from One IP Address

[Persiko, Mark]

Hello,
We have customers who want to name serve multiple hostnames off of a single IP address.  I am aware of two objections to this practice (feel free to correct my thinking here):

1)  Resolvers (most, or many, or some?) will only use the first hostname received in an answer to a PTR query for an IP address, and will throw the rest away anyway, thus causing indeterminate behavior.

2) Too many PTR records (or resource records of any type, for that matter) will cause a name server to send a response packet via TCP, if the maximum allowable UDP packet size is exceeded by the size of the response.  Too many such response packets clog network resources.

I have yet to determine the customers' true business objectives, but I am assuming that they are either or both of:

1) A customer has multiple e-mail domains, but only a single, public IP address, and wants all e-mail domains names to show up in reverse DNS lookups.

2) A customer is hosting multiple, virtual web sites from a single, public IP address, and wants the reverse lookup for the IP address to correspond to all web site FQDN's.

Any thoughts on this are most welcome, especially on how to accomplish the same objectives in other ways.

Thanks in advance!

- Mark

- Mark C. Persiko, Level 3 Communications
- mark.persiko at level3.com<mailto:mark.persiko at level3.com>