Well, assuming you want to stick with this regex for ip's (which allows things like 999.012.4231.31245 - see Matching an IP address), you could just define it beforehand:

my $ip = qr/\d+\.\d+\.\d+\.\d+/;
foreach $line (@connections) {
       if ($line =~ /^\s*($ip):\d+
                 \s*->\s*($ip):\d+
                 \s*->\s*($ip)/x) {
               $client_ip{$1}{$iteration}++;
               $vips{$2}{$iteration}++;
               $frontend{$3}{$iteration}++;
       }
}
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-- Dan