Firewall list generator
Turn the announced prefixes of one or more AS numbers into a block list for nginx, ipset, nftables, iptables or MikroTik, merged into the fewest blocks.
Notes
The list is built from the routes the network announces in BGP, so it covers what is reachable from that AS today. Overlapping and adjacent prefixes are merged. It is not a list of every address the company owns.
Blocking an AS blocks everyone behind it: customers, mail servers and often unrelated services. Large ISPs and cloud providers carry many legitimate users. Test on a small scope first and keep the list updated, because routes change.
For scripts, the same list is available as plain text: /api/v1/tools/firewall?asn=AS13335&format=nginx. It counts as a bulk request.