It seems to me like you've got something in reverse. fork returns undef on failure, 0 to the child, and a pid to the parent. The child, in your code, does nothing.
This is a semaphore like solution to your code:

my $i = 3; # how many simultaneous checks

$SIG{CHLD} = sub { $i++; wait } # or something

# if your signals are safe you may
# want to keep a hash of PIDs and
# the ip's they're associated with,
# and have SIGCHLD's handler print
# out the info and test result based
# on $? and the return value from wait.
# You should exit the child with a
# status which you may check. if the
# open failed exit with a nonzero value.

have running
foreach $remote (@iplist){
    sleep until ($i); # SIGCHLD will wake us. if it wasn't sigchld we 
+should go back to sleep.
    foreach $port (@port_range){
        if (fork){
            $i--; # empty the reservoir
        } else {
            # ping something
            exit ($test_failed) ? 1 : 0; # exit with a proper value
        }
    }
}
[download]

And a regular one:

foreach my $remote (@iplist){
    foreach my $port (@iprange){
        if (my $pid = fork){
            waitpid, $pid;
            print "$remote on $port test finished...";
            # check $?
        } else {
            # check stuff
            exit ( $test_succeeded ) ? 1 : 0;
        }
    }
}
[download]

Update: Suddenly I wondered - if you don't need to check for many at a time, why are you forking?

-nuffin
zz zZ Z Z #!perl