Get the origin ASN(s) for the name-server set for a domain using dig and the Cymru Origin-AS WHOIS service.

ns-origin.sh

#!/usr/bin/env bash

if [[ -z $1 ]]; then
	echo "Usage: $0 {domain}"
	exit 1
fi

DOMAIN="$1"
SERVER="whois.cymru.com"
PORT="43"

exec 3<>/dev/tcp/${SERVER}/${PORT}
echo "begin" >&3
dig +nssearch $DOMAIN |awk '{print $11}' >&3
echo "end" >&3
echo >&3

while read -t 2 line; do
	echo $line
done <&3

exec 3<&-
exec 3>&-
exit $?