Prefix Compression for Covering Route Updates in FIB Tables
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Solution Overview
Problem
Network devices face inefficiencies in processing changes to covering routes due to the need to check and update compressed routing prefix entries, leading to increased processing and resource usage, as well as potential packet loss or incorrect forwarding.
Innovation Solution
Implement a prefix compression technique that stores multiple routing prefixes in a single forwarding entry, using a dual table lookup feature to resolve holes in the compressed routing prefixes to a special predefined value, allowing the network device to ignore the result of the search result of the lookup in the result of the lookup table, and instead, use the result of the lookup performed on the LPM table to determine how to forward the packet, and instead, use the result of the lookup performed on the EM table to determine how to forward the packet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If prefix compression technique is used to store multiple routing prefixes in a single forwarding entry, then the quantity of routing table entries is reduced, but processing overhead increases when covering routes change due to the need to check and update compressed entries
Solution Approach 1:
The patent divides the forwarding table into two separate tables: an exact match (EM) table that stores compressed routing prefixes, and a longest prefix match (LPM) table that stores individual routing entries. This segmentation allows the system to maintain the space efficiency of prefix compression while avoiding the complexity of updating compressed entries, as the LPM table can be updated independently without affecting the EM table structure.
Solution Approach 2:
The patent introduces a dual-table lookup mechanism that acts as an intermediary between the compressed EM table and the detailed LPM table. When a route change occurs, the system can update the LPM table without propagating changes through the compressed EM table, thus reducing processing overhead. The intermediary lookup process resolves packets by checking both tables, maintaining forwarding accuracy while simplifying update operations.
2Volume of stationary object
If prefix compression is implemented, then memory usage is reduced, but convergence speed decreases due to additional checking and updating operations
Solution Approach 1:
By segmenting the forwarding information into two separate tables (EM and LPM), the patent enables independent update operations. When a route change occurs, only the LPM table needs to be updated, while the EM table remains unchanged. This segmentation eliminates the need to propagate updates through compressed entries, significantly improving convergence speed while maintaining memory efficiency.
Solution Approach 2:
The patent performs preliminary compression of routing prefixes into the EM table during table construction, organizing them in a hierarchy-based structure. This preliminary action allows the system to maintain compressed representations without requiring real-time decompression or updates during route changes, thus preserving both memory efficiency and convergence speed.
3Volume of stationary object
If compressed routing prefixes are used, then forwarding table size is reduced, but packet forwarding accuracy may deteriorate due to holes in compressed prefixes
Solution Approach 1:
The patent uses the LPM table as an intermediary to resolve packets that match holes in the compressed EM table. When a packet's destination address matches a compressed prefix in the EM table but corresponds to a hole (a more specific route not explicitly stored), the system consults the LPM table to find the appropriate next hop. This intermediary mechanism ensures accurate packet forwarding while maintaining the space efficiency of prefix compression.
Solution Approach 2:
The patent segments forwarding information into two complementary tables: the EM table handles exact match cases with compressed prefixes, while the LPM table handles longest prefix match cases including holes. This segmentation ensures that each table is optimized for its specific function, with the LPM table providing the detailed routing information needed to accurately resolve packets that fall into compressed prefix holes.
Data Source
AI summary
A network device uses prefix compression to program routes in a forwarding information base (FIB) in a longest prefix match (LPM) table or an exact match (EM) table. The network device compresses routes of a certain prefix length in the FIB into a single entry in the EM table. For a compressed prefix that does not correspond to a route in the FIB (hole), the network device associates the hole with a special value rather than the prefix of a covering route. When the network device receives a packet that matches a hole, the lookup performed on the exact match table results in the special value. In response, the network device uses the result of the lookup performed on the LPM table to determine how to forward the packet.