Now that we’ve looked at how the RPKI structure is built and understand the basics of Internet routing, we can look at how RPKI can be used to make BGP more secure.
RPKI provides a set of building blocks allowing for various levels of protection of the routing system. The initial goal is to provide route origin validation, offering a stepping stone to providing path validation in the future. Both origin validation and path validation are documented IETF standards. In addition, there are drafts describing autonomous system provider authorisation, aimed at providing a more lightweight, incremental approach to path validation.
Route Origin Validation¶
With route origin validation (ROV), the RPKI system tries to closely mimic what route objects in the IRR intend to do, but then in a more trustworthy manner. It also adds a couple of useful features.
Origin validation is currently the only functionality that is operationally used. The five RIRs provide functionality for it, there is open source software available for creation, publication and use of data, and all major router vendors have implemented ROV in their platforms. Various router software implementations offer support for it, as well.
Route Announcement Validity¶
When a network operator creates a ROA for a certain combination of origin AS and prefix, this will have an effect on the RPKI validity of one or more route announcements. Once a ROA is validated, the resulting object contains an IP prefix, a maximum length, and an origin AS number. This object is referred to as validated ROA payload (VRP).
When comparing VRPs to route announcements seen in BGP, RFC 6811 describes their possible statuses, which are:
The route announcement is covered by at least one VRP. The term covered means that the prefix in the route announcement is equal, or more specific than the prefix in the VRP.
The prefix is announced from an unauthorised AS, or the announcement is more specific than is allowed by the maxLength set in a VRP that matches the prefix and AS.
The prefix in this announcement is not, or only partially covered by a VRP.
Anyone can download and validate the published certificates and ROAs and make routing decisions based on these three outcomes. In the Using RPKI Data section, we’ll cover how this works in practice.
Currently, RPKI only provides origin validation. While BGPsec path validation is a desirable characteristic and standardised in RFC 8205, real-world deployment may prove limited for the foreseeable future. However, RPKI origin validation functionality addresses a large portion of the problem surface.
For many networks, the most important prefixes can be found one AS hop away (coming from a specific peer, for example), and this is the case for large portions of the Internet from the perspective of a transit provider - entities which are ideally situated to act on RPKI data and accept only valid routes for redistribution.
Furthermore, the vast majority of route hijacks are unintentional, and are caused by ‘fat-fingering’, where an operator accidentally originates a prefix they are not the holder of.
Origin validation would mitigate most of these problems, offering immediate value of the system. While a malicious party could still take advantage of the lack of path validation, widespread RPKI implementation would make such instances easier to pinpoint and address.
With origin validation being deployed in more and more places, there are several efforts to build upon this to offer out-of-band path validation. Autonomous system provider authorisation (ASPA) currently has the most traction in the IETF, and is described in these drafts: draft-azimov-sidrops-aspa-profile and draft-azimov-sidrops-aspa-verification.