For IRC, the virtual host doesn't even have to be real.. on Freenode, it's not uncommon for someone to have nick@unaffiliated/account and all that requires is a private message to one of the several network operators, full procedure is on their FAQ somewhere.
To avoid contacting the operators of the IRC network, an ISP assigned PTR record needs to point to a real domain that has a matching A record, so having a static IP is an absolute requirement.
Generally it's a complicated procedure which needs the cooperation of a competent professional on both ends, it's more common for VPS/dedicated server providers to do this as generally they are allotted IP ranges by their ISP and are given control over PTR records.
Learning more about some of those protocols is probably advisable, it's generally an extensive topic and doing some reading of your own is encouraged.
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