To debug drops, use "watch -n 1 drops.pl"

drops.pl

#! /usr/bin/perl

use warnings;
use strict;

use Data::Dumper;
#
sub read_udp {
	my $fn = shift;
	my $drops = shift;
	my $fh;
	open($fh, '<', $fn) or die "$fn: $!\n";
	<$fh>;

	while(<$fh>) {
		chomp;
        s/^\s*//;
		my @f = split(/\s+/);
        next if $f[12] eq '0';
		$drops->{$f[9]} = $f[12];
	}
	close $fh;
}

my %drops;
read_udp('/proc/net/udp', \%drops);
read_udp('/proc/net/udp6', \%drops);

my $arg = shift;
$arg ||= 'sport = 5300 or sport = 53';
my @port = qq/$arg/;

my $fh;
open($fh, '-|', 'ss', '-nleu') or die "ss: $!\n";
# udp    UNCONN     0      0      194.109.20.106:5300                  *:*                   ino:31851 sk:2bf <->
# udp    UNCONN     0      0      127.0.0.1:5300                  *:*                   ino:30795 sk:2c0 <->
# udp    UNCONN     0      0        2001:888:0:104::6a:5300                 :::*                   ino:31852 sk:2df v6only:1 <->
# udp    UNCONN     0      0       ::1:5300                 :::*                   ino:31850 sk:2e0 v6only:1 <->
my $hdr = 0;
while (<$fh>) {
	if ($hdr == 0) {
        chomp;
		print "$_ Drops\n";
		$hdr = 1;
		next;
	}
    next unless /UNCONN/;
    next unless /:53(00)?\s/;

	my @f;
    push @f, $1 while (s/^(\S+\s*)//);
    #print Dumper(\@f);
    my $field = 5;
	my $inode = $f[$field];
    my $l = length($inode);
    $inode =~ s/\s*ino:(\d+)\s*/$1/;
	my $d = $drops{$inode} || 0;
	$f[$field] = sprintf("%-*d", $l, $d);
	print join('', @f); # if $d > 0;
}
close $fh;