#!/usr/bin/perl
#
use strict;
use warnings;
use Data::Dumper;

my $text = <<"EOT";
System Information

    The following parameters were set on the configured target:
        hostname:           markov1
        IP address:         10.X.X.11
        IP address:         10.X.X.2
        IP address:         X.X.X.37
        gateway IP address: 10.X.X.1
        gateway IP address: X.X.X.1
        gateway IP address: X.X.X.1
        gateway IP address: X.X.X.1
        time zone:          MET-1METDST
        DNS IP address:     X.X.X.110
        DNS IP address:     X.X.X.142
EOT

my @lines = split /\n/, $text;
my @ips   = grep{ /(?<!DNS )IP\s+address:/ and /(?<!gateway )IP\s+address:/ }@lines;
print $_,"\n" for @ips;

rbaecker@test $ perl ip.pl
        IP address:         10.X.X.11
        IP address:         10.X.X.2
        IP address:         X.X.X.37