1. Introduction

1. Introduction

ISPs delegate IP addresses or prefixes to users, and cloud providers assign customers prefixes of specific sizes. Content providers often need to understand the correct end-site prefix size for blocklisting, throttling, rate limiting, CAPTCHA behavior, and geolocation, especially for IPv6.

This document specifies how to augment the Routing Policy Specification Language (RPSL) [RFC2725] inetnum: class to refer to prefixlen files and how to use those files. In places where inetnum: is used, inet6num: is also assumed [RFC4012]. Section 6 defines an optional RPKI-based authentication mechanism.