#! /usr/bin/perl

use strict;

#BUILD IP LIST
open(IPS, 'ip.txt') || die "Can't open IP.txt: $!\n"; 
my $iplist = join('|', map {chomp;quotemeta} <IPS>);
close(IPS);
my $re = qr/$iplist/;

#READ IN LOG FILE
my @log = map {chomp;$_} <DATA>;

#Check for matches
my @matches = grep /$re/, @log;

print "$_\n" foreach(@matches);

__DATA__
1.1.2.1
1.3.4.5
192.168.0.1
1.2.3.4
4.5.6.7
10.0.0.1
[download]

ip.txt

192.168.0.1
1.1.1.1
10.0.0.1
[download]

Output:
192.168.0.1
10.0.0.1

Update: Add contents of ip.txt, which made the output make more sense.
Combined 2 map statements into 1 when reading in ip.txt.