use Net::Telnet::Cisco;

for ($i = 1; $i <= 254; $i++){
  
  $device = "172.16.$i.251";

  my $session = Net::Telnet::Cisco->new(Host => "$device",
            Input_log => "perllogrouter/router$i.log",);

   eval { $session->login('admin', 'admin') or die "Could not connect 
+to $device" };