Monitoring As-Sets And Why They Matter
Cloudflare, Friday, September 26th, 2025
An AS-SET, not to be confused with the recently deprecated BGP AS_SET, is an Internet Routing Registry (IRR) object that allows network operators to group related networks together.
AS-SETs have been used historically for multiple purposes such as grouping together a list of downstream customers of a particular network provider. For example, Cloudflare uses the AS13335:AS-CLOUDFLARE AS-SET to group together our list of our own Autonomous System Numbers (ASNs) and our downstream Bring-Your-Own-IP (BYOIP) customer networks, so we can ultimately communicate to other networks whose prefixes they should accept from us.