According to the documentation, Net::Ping tries a tcp connection to the echo port on the target machine. Do the target machines have an echo daemon running?

Well done for providing some code to illustrate the problem. Unfortunately what your code demonstrates is merely that the target addresses are not responding to the Net::Ping tests, it passes no judgement on whether or not the addresses are "recognized".

use strict;
use warnings;

use Test::More tests => 7;
use Net::Ping;

my $p = Net::Ping->new;
for my $host (qw/www.perlmonks.org tcpbin.com/) {
    ok $p->ping ($host), "$host pinged";
}
for my $host (qw/www.ibm.com www.whitehouse.gov/) {
    ok !$p->ping ($host), "$host blocks pings";
}
for my $host (qw/lsdfskf wocka.wocka 192.168.1/) {
    ok !$p->ping ($host), "$host doesn't respond because it won't reso
+lve";
}
[download]

Note how the second and third sets behave the same in terms of the false return value from the ping method despite failing in different ways.