ip-to-asn-lookups.txt

# got a list of IPs you need to do lookups for?
# map them back to their ASes with Team Cymru's DNS-based IP-to-ASN lookup service...
$ for asn in $(
    for ip in $(cat ips.txt); do
      revip=$(echo $ip | awk -F. '{print $4"."$3"."$2"."$1}');
      dig +short $revip.origin.asn.cymru.com TXT;
    done | cut -d ' ' -f 1 | cut -c 2- | sort | uniq
  );
  do dig +short AS$asn.asn.cymru.com TXT;
  done