Assuming the IP address will always have a port number appended to it:

use Regexp::Common qw( net );

while ( <DATA> ) {
    while ( m/($RE{net}{ipv4}:\d+)/g ) {
        print $1, "\n";
    }
}

__DATA__
[LAN access from remote] from 213.114.117.222:52582 to 10.0.0.3:5697, 
+Monday, July 23,2012 19:42:26
[download]

If you're only interested in those IP's that access "10.0.0.x:y", this will do it:

while( m/(10\.0\.0\.\d+:\d+)/ ) {
    print $1, "\n";
}
[download]

If you want something else then let's back up and discuss what you're trying to accomplish first.