Translations:FAQ/131/en

Another example: 4.3.2.1.in-addr.arpa domain name pointer somehost.domain. somehost.domain has address 5.5.5.5 In this case your own name server is fine, it is sending replies. But the information does not match: reverse dns resolved 1.2.3.4 to somehost.domain, however, when double checking this by resolving somehost.domain we got 5.5.5.5 back. Since forward DNS and reverse DNS don't match the user will not have a hostname on IRC. That's how it works, otherwise everyone could spoof their own hosts... In this case the owner of the domain and/or the IP could (or should) fix their DNS entries to make them match.
 * 1) host 1.2.3.4
 * 1) host somehost.domain