use List::Util    qw( uniq );
use Sort::Natural qw( natsort );

my %data;
while ( <$fh> ) {
   chomp;
   my ( $ip, @hosts ) = split;
   push @{ $data{ $ip } }, @hosts;
}

for my $ip ( natsort keys( %data ) ) {
   my @hosts = natsort uniq @{ $data{ $ip } };
   say join "\t", $ip, @hosts;
}

##</code><code>##

use Sort::Natural qw( natsort );

my %data;
while ( <$fh> ) {
   chomp;
   my ( $ip, @hosts ) = split;
   ++$data{ $ip }{ $_ } for @hosts;
}

for my $ip ( natsort keys( %data ) ) {
   my @hosts = natsort keys %{ $data{ $ip } };
   say join "\t", $ip, @hosts;
}