BGP Update Aggregation for Multipath Route Efficiency
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Solution Overview
Problem
Advertising multiple routes with different attributes for a given prefix in BGP updates leads to spread-out updates, causing additional calls to download routes to the forwarding information base, new reachability information advertisements, and multiple instances of multipath calculations, which is disadvantageous.
Innovation Solution
Ordering BGP UPDATE messages using the destination prefix to send routes with the same prefix and different attribute values in adjacent messages, or sending routes with the same set of attribute values in the same message, thereby reducing the spread of updates and improving routing information base learning rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple routes with different attributes for a given prefix are advertised in spread-out BGP updates, then the BGP protocol allows flexible route advertisement, but it causes additional calls to download routes to the forwarding information base, new reachability information advertisements, and multiple instances of multipath calculations
Solution Approach 1:
The patent combines multiple BGP update messages carrying routes for the same prefix into a single aggregated update message. The BGP speaker identifies updates with the same destination prefix and merges them, consolidating multiple route advertisements into one message that contains all the routes. This reduces the number of separate update transmissions and improves RIB learning efficiency while preserving the ability to advertise multiple paths with different attributes.
2Loss of information
If multiple BGP updates are sent for routes with the same prefix, then complete route information is provided to receivers, but the updates are spread out causing increased processing workload and reduced learning rates
Solution Approach 1:
The BGP speaker performs preliminary aggregation of update messages before transmission. By identifying and combining updates with the same destination prefix in advance, the speaker prepares consolidated update messages that contain complete route information. This preliminary action ensures that receivers receive all necessary route information in a single update rather than multiple spread-out updates, reducing processing time and improving efficiency.
3Ease of operation
If BGP speakers send multiple paths for the same prefix in separate updates, then each path can be advertised with its specific attributes, but the spread-out nature of updates increases the complexity of route processing
Solution Approach 1:
The patent merges multiple update messages into a single aggregated update that contains all routes for a given prefix. Each route within the aggregated update retains its specific attributes (such as AS_PATH, NEXT_HOP, LOCAL_PREF), but they are all delivered together in one message. This approach preserves the ability to specify individual route attributes while reducing processing complexity by eliminating the need to handle multiple separate update messages.
Data Source
AI summary
BGP can advertise multiple routes for same prefix via BGP add path (RFC 7911). BGP attempts to pack prefixes with same path attributes into the same BGP update message. Protocol nexthop is one of the path attributes. Since these BGP add paths routes usually have different protocol nexthops, different routes for a single prefix could end up being spread out when being advertised. That may, in turn, result in additional calls to download routes to FIB, advertisement to peers and multiple runs of multipath calculation for the same prefix when multipath is configured. To help avoid this situation, when BGP advertises add-path routes, BGP can send the multiple paths for the same prefix in the adjacent update messages. BGP can use extended Network Layer Reachability Information (NLRI) field to carry nexthop along with its associated prefix in BGP update message to send plain IPv4 unicast routes. In addition, BGP reachability information can be encoded in MP_REACH_NLRI attribute with which protocol nexthop information is carried along with its own prefix in the extended “NLRI” field. A BGP speaker can use some data structure to link these routes for the same prefix and put multiple routes for the same prefix in adjacent or even same BGP update messages.