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General Global Routing Operations BMP Filtering RIBs in BMP (BGP Monitoring Protocol) can be desirable for several use-cases like, for example, limiting the amount of data a collector station has to process or allow a sender to export only a certain afi/safi of interest. This document defines an indicator to inform a collector station that a Adj-Rib-In or Adj-Rib-Out data feed is being filtered at the BMP exporter. This document updates RFC 7854.

While Section 6.1 of does define a way to mark a Loc-Rib as filtered, there is no equivalent mechanism for Adj-Rib-In RFC7854 and Adj-Rib-Out RFC8671. This can be addressed through the introduction of a Peer F Flag in the "BMP Peer Flags for Peer Types 0 through 2" registry.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Marking the Adj-RIB-In or Adj-RIB-Out data feed in a BMP session as filtered can be informative to the rest of the data pipeline that they should not make decisions assuming that this stream is transmitting all the information about it. A BMP exporter, typically a router, need to send Route Monitoring updates per peer while meeting several requirements, such as minimizing CPU consumption, avoiding impact on key routing functions, and providing near real-time updates to the collector. As network scale increases, satisfying these requirements becomes increasingly challenging. Therefore, any mechanism that enables data filtering is beneficial. On the BMP monitoring station, typically a software collector, excessive data imposes costs on storage and processing. Reducing the volume of data limited to key points of interest (for example, edge peering), can help alleviate these costs.

As a recap, a BMP session is regarded as carrying Adj-Rib-In by defining the Peer Type to 0, 1 or 2 values and setting the O flag to zero (0) in the BMP Peer Flags (for Peer Types 0 through 2) registry. Similarly, Adj-Rib-Out is set by defining the Peer Type to 0, 1 or 2 values and setting the O flag to one (1) in the BMP Peer Flags (for Peer Types 0 through 2) registry. Both Adj-Rib-In and Adj-Rib-Out can be further defined as Pre-Policy, setting the Peer L Flag to zero (0), or Post-Policy, setting the Peer L Flag to one (1). For both Adj-Rib-In and Adj-Rib-Out, for both Pre-Policy and Post-Policy cases, a new Peer F Flag is defined in the "BMP Peer Flags for Peer Types 0 through 2" registry. If the RIB was filtered, the flag MUST be set to one (1). Filtering in this document refers to the BMP sender applying a filter to the data sent to the BMP receiver. The F flag does not impact on Statistics Report messages. In Statistics Report messages, the F flag MUST be set to zero (0) and SHOULD be ignored by the BMP receiver. This document does not modify the semantics of any existing BMP Statistics Type. If a change to BMP export filtering changes the set of routes reported for a RIB view, the sender MUST send a Peer Down Notification followed by a Peer Up Notification before reporting the changed RIB view.

The F flag indicates that the view reported to the BMP receiver is filtered. It does not describe the filtering criteria or identify the routes that were filtered by the BMP sender to the BMP receiver. The definition and communication of filtering criteria are outside the scope of this document. It is recommended that when filtering RIBs, the VRF/Table Name TLV - as defined in RFC9069 and BMP Peer Up Namespace - is specified to a meaningful string that can help discriminate the nature of filtering. The VRF/Table Name TLV can be either set in the Peer Up message, so to implicitly apply to all NLRIs received by the peer, or set via a Group TLV in Route Monitoring messages, to explicitly apply to all NLRIs in the group. Going down the Peer Up model is certainly optimal on the wire and simplifies packing at the sender side; going down the Route Monitoring model, instead, allows the receiver side to operate non-contextually (ie. no need to look back at the Peer Up to make due associations). Filtering configuration may be exposed through management-plane mechanisms. For example, the BMP YANG data model defines configuration for filtering Route Monitoring messages.

The security considerations of RFC 7854 apply. If the F flag incorrectly indicates that a filtered RIB view is unfiltered, a BMP receiver may incorrectly treat an incomplete view as complete, potentially resulting in incorrect operational or security analysis. The F flag represents information supplied by the BMP sender and does not independently verify the completeness of the reported RIB view.

This document asks IANA to add a new F Flag to the "BMP Peer Flags for Peer Types 0 through 2" registry. The recommended value for the registry is 4.

&RFC2119; &RFC8174; &I-D.ietf-grow-bmp-yang;

The authors would like to thank Jeff Haas for his valuable input.