Marking Announcements to BGP Collectors

BGP route collectors such as RIPE RIS and Route Views are used by both operators and researchers. Unfortunately, one can not tell paths announced to a collector are solely from the ISP's customer cone (one's own prefixes and the closure of those to whom transit is provided; i.e. what one would announce to a peer), include internal routes (e.g. inter-router links), or external paths learned via peering or transit. This greatly reduces the utility of the collected data, and has been a cause of much pain over the years. This document suggests the use of BGP communities to differentiate between these categories. In 2006, attempted a similar goal but failed to gain traction in the operational community. We believe this was due to its unnecessary complexity. This document proposes two much simpler marking schemes and, if published, will obsolete . This document describes 'in-band' signaling, i.e. what a user of the raw BGP data from a collector can see. The collector operation is assumed to collect a lot more meta-data about the participants, e.g.: contact details, location if remote, etc.

When an operator uses a collector to look at an ISP's announcement of a prefix, it is very useful to know if the ISP also announced it to their customers and/or peers/transits. Researchers want to differentiate similarly in order to understand expected route propagation. One usually wishes to ignore any internal-only routes, e.g. inter-router point-to-point links, an ISP may announce to the collector, as they would not be announcing them to peers, transits, or customers. I.e. they would not be used operationally. An ISP is expected to announce customer routes to their customers, and announce customer routes to their external peers and transits. In general, one does not need to differentiate whether the ISP will announce to peers or transits; and the ISP may not wish to expose the business relationships with external providers. So this document do not propose to differentiate peers from transit providers.

We consider only three categories of announcements: One's own prefixes and the closure of those to whom transit is provided including routes announced by BGP customers, static prefixes used for non-BGP customers, datacenter routes, etc. Routes learned from peers and transit providers which the ISP would normally announce to customers but not to peers. Often, ISPs do not announce such routes to collectors. But, as there is no general practice, this category is important to mark. ISPs occasionally announce to the collector Internal point to point and other routes they would not normally announce to customers, peers, or transit providers.

BGP announcements to route collectors SHOULD be marked with communities indicating into which category the announcement falls. As most collector peers already use community markings similar to these, but ad hoc, the additional effort should be trivial. The ASN in the marking SHOULD be that of the collector peer. The communities were selected from community values which were unused at the time of this document and SHOULD be as follows: ASs which do not peer with collectors MAY also choose to use these markings. Category Community Customer Cone ASN:64994 External Route ASN:64995 Internal Route ASN:64996 Community Markings

Alternatively, should marking at the path granularity be considered too revealing, the collector peer could announce a single well-known prefix, for example 10.10.10.10/10, with one or more of the community markings as above, describing the set of paths being announced to the collector.

As the number of categories is intentionally minimal, an IANA registry should not be needed.