rdig

#!/bin/bash
# (c) 2020 Leif Sawyer
# License: GPL 3.0 (see https://github.com/akhepcat/)
# Permanent home:  https://github.com/akhepcat/Miscellaneous/
# Direct download: https://raw.githubusercontent.com/akhepcat/Miscellaneous/master/rdig
# 
PROG=${0##*/}
# rdig host.3ld.2ld.dom
#
#  walks backward until it finds the authoritative name server for each tld (excepting '.')
#

FQDN=${1}

FQDN=${FQDN,,}	#lowercase it all
FQDN=${FQDN//[0-9a-f:.]/}  #zero out bare IPv4/IPv6 addresses

if [ -z "${FQDN}" ];
then 
	echo "Usage:"
	echo -e "\t${PROG} [fqdn]"
	exit 1
fi

#restore the original domain from the command line
FQDN=${1}

myfqdn=${FQDN}

while [[ "${myfqdn}" != "${FQDN##*.}" ]]
do
	echo "testing ${myfqdn}"
	MYSOA=$(dig +short "${myfqdn}" SOA)
	if [ -n "${MYSOA}" ]
	then
		echo -e "${myfqdn} \t IN \t SOA ${MYSOA}"
		
		MYNS=$(dig +short "${myfqdn}" NS)
		if [ -n "${MYNS}" ]
		then
			for NS in ${MYNS}
			do
				NSIP=$(dig +short ${NS})
				echo -e "${myfqdn} \t IN \t NS ${NS} \t A \t ${NSIP}"
			done
		fi
	else
		echo "no SOA for ${myfqdn}"
	fi
#	dig +noall +answer "${myfqdn}" NS
	myfqdn=${myfqdn#*.}
	echo ""
done