Ruijie RG-S2900G-E Series, Configuration Manual

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Configuration Guide IPv4 Express Forwarding Configuration
IPv4 Express Forwarding
Configuration
Overview
To adapt to the needs of high-end devices, currently we are using "Prefix Tree + Adjacency"
Express Forwarding model to achieve fast forwarding. In case the device only caches partial
information of the core routing table, the central CPU will have to add cache entries again if the
cache fails. Express Forwarding maintains a mirror image of the entire core routing table in order
to relieve CPU load and guarantee the stability of routing performance.
Express Forwarding uses the following two components to create the mirror image of routing
table:

Prefix Tree
This is an IP prefix tree organized as per the longest matching principle to look up adjacent nodes.
In practice, the data structure for constructing Prefix Tree is generally different form the Radix
Tree of core routing table. A data structure called M-Tries Tree is used to realize faster lookup.
The Prefix Tree created by M-Tries Tree will consume more memory than Radix Tree, and the
update of Prefix and node information will be comparatively time-consuming, but higher lookup
performance can be realized.

Adjacency
Adjacent node, including the output interface information of routed packets, such as next hop list,
next processing unit, link-layer output encapsulation and etc. When packets matches with such
adjacent node, the packets will be encapsulated and forwarded by calling the transmit function
of this node. To facilitate lookup and update, the adjacent nodes will generally form a hash table.
To support router load balancing, the next-hop entries of adjacent nodes are organized into a
load balancing table. Adjacent node may not include next-hop information, or may include the
index number of next processing unit (such as other line cards, multi-service card and etc).
Express Forwarding comprises three steps:
1. Express Forwarding to de-encapsulate packets;
2. Use Prefix Tree to look up the next-hop adjacent node of packet route;
3. After matching to the next-hop adjacent node, the final egress interface of
packets will be determined according to the information of adjacent node,
and packets will be encapsulated according to the type of egress interface.
Express Forwarding table Maintenance and Monitoring
The express forwarding module only passively receives and maintains the external routing
information, and will not actively insert or delete any routing information. Therefore, express
forwarding mainly provides the statistics of existing routes.