BMP Extension for BGP Path Attribute Sets and Statistics

3.1. BMP Attribute Set Declaration Message

The BMP Attribute Set Declaration Message is used to register a new unique BGP Path Attribute Set or explicitly unregister an existing one.¶

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Attribute Set ID (AS-ID)                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Action| Reserved                                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                Path Attributes Length (2 Octets)              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Path Attributes (Variable Length)                  |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Fields:¶

• Attribute Set ID (AS-ID) (32 bits): A 32-bit unsigned integer assigned locally by the monitored router to uniquely identify a specific BGP Path Attribute Set during the active session lifecycle. The value MUST NOT be 0 (0x00000000 is reserved).¶

• Action (4 bits): Specifies the operation to be performed on the target AS-ID:¶

  • 0x1 (REGISTER): Indicates the declaration of a new unique Path Attribute Set. The receiver MUST associate the provided Path Attributes with this AS-ID.¶

  • 0x2 (UNREGISTER): Indicates that the AS-ID is explicitly deleted. The receiver MUST purge or mark inactive the Path Attribute Set associated with this AS-ID.¶

  • Values 0x0 and 0x3-0xF are reserved for future use and MUST be ignored on receipt.¶

• Reserved (28 bits): Reserved for future extension. MUST be set to 0 by the sender on transmission and MUST be ignored by the receiver upon receipt.¶

• Path Attributes Length (16 bits): A 16-bit unsigned integer specifying the total length, in octets, of the Path Attributes field.¶

  • When Action = 0x1 (REGISTER), this field MUST be greater than 0.¶

  • When Action = 0x2 (UNREGISTER), this field SHOULD be set to 0.¶

• Path Attributes (Variable Length): Contains zero or more BGP Path Attributes formatted as specified in Section 5 of [RFC4271]. This field is evaluated only when Action = 0x1 (REGISTER).¶

3.2. BMP Attribute Count Update Message

The BMP Attribute Count Update Message is used to convey prefix volume statistics bound to a previously registered AS-ID.¶

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Attribute Set ID (AS-ID)                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Op    | Mode  | Reserved                                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       NLRI Count / Delta                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Fields:¶

• Attribute Set ID (AS-ID) (32 bits): A 32-bit unsigned integer referencing a valid AS-ID previously announced via a BMP Attribute Set Declaration Message (Action = REGISTER).¶

• Op (Operation Type) (4 bits): Defines how the receiver interprets the value in the NLRI Count / Delta field:¶

  • 0x1 (ABSOLUTE_COUNT): The value represents the exact total number of prefixes (NLRIs) currently bound to this AS-ID.¶

  • 0x2 (DELTA_ADD): The value represents an incremental addition (+N) to the current prefix count associated with this AS-ID.¶

  • 0x3 (DELTA_DEL): The value represents an incremental subtraction (-N) from the current prefix count associated with this AS-ID.¶

  • 0x4 (ZERO_REF): Indicates that the prefix count bound to this AS-ID has dropped to 0. The NLRI Count / Delta field MUST be set to 0.¶

• Mode (4 bits): Indicates the operational context under which this report was generated:¶

  • 0x1 (EVENT_DRIVEN): Sent immediately in response to a routing state change (e.g., prefix addition/withdrawal).¶

  • 0x2 (PERIODIC): Sent as part of a scheduled, regular telemetry sweep.¶

• Reserved (24 bits): Reserved for future extension. MUST be set to 0 on transmission and ignored on receipt.¶

• NLRI Count / Delta (32 bits): A 32-bit unsigned integer representing either the total prefix volume or the change delta, interpreted according to the Op field.¶

3.3. BMP Message Type Allocations

This document defines two new BMP message types to be registered by IANA under the "BMP Message Types" registry:¶

• BMP Message Type = TBD1: Attribute Set Declaration Message (used to register or unregister canonical path attribute sets).¶

• BMP Message Type = TBD2: Attribute Count Update Message (used to report prefix volume statistics associated with a specific AS-ID).¶

4.1. Attribute Set Declaration Logic (Immediate Trigger)

1. The router MUST monitor unique Path Attribute combinations in its RIB.¶

2. When a route arrives with a previously unseen Path Attribute combination, the router MUST immediately allocate a new AS-ID and transmit an Attribute Set Declaration Message (Action = REGISTER).¶

4.2. Attribute Count Update Modes

An implementation SHOULD allow the operator to configure one of the following export modes for Attribute Count Update messages:¶

Option 1: Event-Driven Mode (Immediate Reporting)¶

• Whenever prefixes associated with an AS-ID are added or withdrawn, the router immediately transmits a Count Update Message using either DELTA or ABSOLUTE values.¶

Option 2: Periodic Reporting Mode (Interval Polling + Zero Threshold)¶

• The router suppresses real-time per-route update messages and instead transmits ABSOLUTE count reports for all active AS-IDs at a configured interval (e.g., every 30 seconds).¶

• EXCEPTION: If the prefix count for any AS-ID drops to 0 prior to the next periodic timer expiration, the router MUST immediately emit a Count Update Message (Op = ZERO_REF, NLRI Count = 0).¶

• Upon emitting or receiving Op = ZERO_REF, the router and server MAY initiate unregistration/garbage collection for that AS-ID.¶

4.3. Session Re-establishment and State Synchronization

When a BMP session between the Monitored Router and the Monitoring Station is established or re-established after a failure:¶

1. The Monitored Router MUST re-advertise all currently active Path Attribute Sets present in its RIB using Attribute Set Declaration Messages (Action = REGISTER) with their corresponding valid AS-IDs.¶

2. Following the attribute declarations, the router SHOULD transmit initial Attribute Count Update Messages (Op = ABSOLUTE_COUNT, Mode = EVENT_DRIVEN) to synchronize current prefix volumes for each AS-ID, ensuring the BMP Monitoring Station rapidly achieves state convergence without waiting for the next periodic polling interval.¶

8.1. Normative References

[RFC2119]

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>.

[RFC4271]

Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, <https://www.rfc-editor.org/info/rfc4271>.

[RFC7854]

Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP Monitoring Protocol (BMP)", RFC 7854, DOI 10.17487/RFC7854, June 2016, <https://www.rfc-editor.org/info/rfc7854>.

[RFC8174]

Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2. Informative References