Although this solution doesn't use split, you can capture the ip between the colon and comma with just a regex--given your file's contents:

use strict;
use warnings;
use 5.010;

say /:(.*),/ while <DATA>;


__DATA__
host1    dns:192.168.243.30,asdf
host2    dns:192.168.243.1,qwert
[download]

I know this doesn't specifically address your "Is there something missing with my code?" question, as the prior comments effectively have, but it may be interesting information to you.

Hope this helps!