Regular expressions should not be used to parse IP addresses because IP addresses can be expressed in several forms...
in reply to Don't Use Regular Expressions To Parse IP Addresses!
There are plenty of situations, such as parsing server logfiles, where four-part IP addresses are a given. In these cases, using a regex is just fine.
The only case I've actually run across in practice where using a regex isn't safe is when parsing URLs where some spammer has obscured an IP address by using a non-standard forms.