A recent analysis has uncovered widespread manipulation of the BGP ORIGIN attribute by transit providers, a practice reportedly affecting a significant majority of BGP paths. The findings indicate that approximately 70% of BGP paths are subject to rewrites of their ORIGIN attribute, a modification apparently undertaken by transit providers to gain traffic advantages. This reported manipulation raises questions about the integrity of BGP route selection and its broader implications for Internet routing.
The BGP ORIGIN attribute is a well-established component of BGP path selection, intended to indicate the origin of a route within an Autonomous System (AS). It typically takes one of three values: IGP (internal to an AS), EGP (external via EGP), or INCOMPLETE (origin unknown or learned via other means). This attribute plays a role in the BGP best path selection algorithm, where a lower ORIGIN value (IGP being preferred over EGP, and EGP over INCOMPLETE) can influence a router to select a particular path. The reported rewrites suggest that transit providers are altering this attribute, presumably from a less preferred value to a more preferred one, to encourage traffic to flow through their networks.
The mechanism of this manipulation likely involves transit ASes intercepting BGP updates and modifying the ORIGIN attribute before re-advertising them to their peers or customers. For instance, a route originally marked as INCOMPLETE might be changed to IGP or EGP, making it appear more authoritative or desirable in the eyes of downstream routers applying the BGP best path selection process. This could effectively steer traffic away from paths that would otherwise be chosen based on the original, unaltered BGP attributes.
The scope of this issue appears to be substantial, with the analysis suggesting nearly 70% of BGP paths are affected. This widespread manipulation could lead to suboptimal routing decisions, as traffic might be directed through less efficient or more congested paths due to an artificially inflated ORIGIN attribute. Such practices could also complicate network troubleshooting and performance analysis, as the reported BGP attributes would not accurately reflect the true origin or characteristics of a route.
Mitigation for this class of BGP attribute manipulation is challenging, as it often occurs within the operational practices of transit providers. Network operators typically rely on the integrity of BGP attributes received from their peers. However, in cases where such manipulation is suspected, operators might employ other BGP path selection mechanisms, such as local preference, AS path length, or MED (Multi-Exit Discriminator), to exert more control over their outbound routing decisions. Filtering BGP updates based on expected ORIGIN attributes could also be considered, though this might be complex to implement at scale without inadvertently disrupting legitimate routes.
The findings underscore a broader tension in Internet routing between established protocol mechanisms and the commercial incentives of network operators. The BGP ORIGIN attribute, like other BGP attributes, relies on a degree of trust among participants in the global routing system. When this trust is undermined by deliberate manipulation for traffic advantage, it can degrade the overall efficiency and predictability of the Internet. The analysis reportedly advocates for the deprecation of the ORIGIN attribute in route selection, suggesting a re-evaluation of its role in an environment where its integrity cannot be consistently assured.
