How to find all of an ISP's ASNs

Hi folks, how to I find all ASNs that belong to an ISP? I want to block access to my IoT cameras from the world other than the two local major ISPs (keeping last Friday in mind!)

Gary B

ripe atlas has this info


Can search here as well.

Luke Guillory
Network Operations Manager

Tel: 985.536.1212
Fax: 985.536.0300

Reserve Telecommunications
100 RTC Dr
Reserve, LA 70084

. . . why would you want to expose them to the public Internet at all?

There are many, many reasons not to do so.


You can use this


Dhia Mahjoub, PhD
Technical Leader, OpenDNS, part of Cisco

Thanks folks, much appreciated

Gary B

as-set if they keep their routing registry updated?

something like this

Normally I use IRR Explorer, but somehow the return is empty


as-set if they keep their routing registry updated?

something like this
AS-RR-Res -

and if that doesn't work try:
[replace the ASN with the ASN of your choice to see the interconnections.]


​Doesn't always work--as it will only show upstream ASNs.

For example, Comcast's backbone AS interconnects their regional ASNs.
However, the regionals don't show up on so
you'd need to find all of them first...with something like[search]=Comcast and/or consult your
favorite route server.

Also Gary, keep in mind these aren't static. I.e. new AS are added/removed
over time. And inferred policy (i.e. hub/spoke) could change too.

But I'm still to you propose to filter by AS?

And what if your neighbor (inside one of those permitted AS) is
compromised? You've just re-exposed your IoT devices' soft white underbelly
again. :frowning: