Validate domain NS records against whois and NS servers.

check-nservers

#!/usr/bin/perl

use strict;
use warnings;
use Storable qw/freeze/;

$Storable::canonical = 1;  # https://www.perlmonks.org/?node_id=127254

die "Usage: $0 domain-name\n" unless @ARGV == 1;
my $domain = shift @ARGV;

open F, "whois $domain |" or die "Cannot run whois: $!\n";
my @nservers = sort map { s/[\.\r\n]+$//; my @a = split; lc $a[$#a] } grep { /nserver:/i or /name server:/i } <F>;
print $_,"\n" foreach "=== WHOIS ===",@nservers;

foreach my $s (@nservers) {
    open F, "host -t ns $domain $s |" or die "Cannot query $s: $!\n";
    my @ns = sort map { s/[\.\r\n]+$//; my @a = split; lc $a[$#a] } grep { /name server/ } <F>;
    next if freeze(\@ns) eq freeze(\@nservers);
    print $_,"\n" foreach "=== $s ===",@ns;
}