Would it generally impact the performance of a firewall if it has to enable a site by domain rather than IP? The context is we have an application that runs on Google Appengine (no fixed IP's) and a question was raised by the IT function of a potential customer that opening their firewall for our application will mean they have to do a reverse DNS lookup on every packet if they enable traffic to our domain. I can't imagine this is a unique situation and I'm wandering if this is a general problem with enabling per domain or specific to a technology choice they have made.
Thanks