advice on ip address allocation for psa domains?

[malone]

We have a server running Plesk 7.5.3 handling the hosting and mail duties for many domains. Until now, we have been using all of the domains primarily resting on a single IP address (virtual hosting), with a few extra IP addresses configured for temporary use.

I am wondering what other people do in regards to allocating IP addresses to hosting clients. Our upstream provider says they will allocate as many IP addresses as we need, but up until now we have only used a minimal amount. Do other people here typically assign a new IP address per hosted domain, assuming they have the IP addresses available from their providers?

The reasons for asking this are my attempts to move towards providing proper reverse dns functionality for all of my hosted domains. I am hoping to cut down on the occasional email messages "lost in delivery" that we occasionally experience. Up until now we have not properly configured reverse DNS, but in the process of doing so, I am wondering whether we should just go all the way and assign each new hosted domain an IP, thus simplifying the work when configuring the reverse DNS (since each IP will map to that single hosted domain).

We currently provide our existing virtualhosting services, where many domains are living on the one IP address. During my reading about reverse DNS, the articles I have read typically frown upon providing multiple PTR records for the same IP address because they are dished out randomly to requesting lookups.

Any advice or past experience on this would be helpful. I would be happy to provide more information if needed.

 

[hardweb]

It's advisable to use IP resources in an intelligent way. Even if your provider is able to give you IP addresses on request, you should put as many domains as possible on a single IP. You must assign IP addresses per domain only when the user wants to use certificates or anonymous FTP. Reverse DNS is sensitive also, but few domains really require this.

All providers have hundread of domains on a single IP.

 

[malone]

That sounds reasonable to me. However, how do I address the problem of remote mailservers? It seems as though remote mailservers (some, not all) are rejecting emails from my server because the IP address does not resolve.

If all of my hosted domains are using a single IP address, how do I address the problem of reverse dns being accurate? Or is this not a concern, and I only ensure the server itself (eg. hosting1.mycompany.com) is mapped back when someone does a reverse dns lookup on the IP address?

I guess i'm confused here as to the implications when there are many domains sharing a single IP, but that IP is supposed to map back onto a name when requested (by remote mailserver, for example).

 

[renhack]

Reverse DNS tests will pass regardless of whether your reverse lookup points back to your server domain or the customers domain. Typically on 99% of the servers out there It just needs to resolve period.

Dont waste valuble IPs on clients that dont need them. Use them for cerificate and client request only.

Multiple PTR records wont get you into trouble unless a client wants to know why a traceroute resolves to some hosted domain other than theirs or yours.

-e