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Igor Putovny 2024-07-10 15:12:49 +02:00
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87
proto/aggregator/aggregator.c
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@ -1,37 +1,78 @@
/*
* BIRD Internet Routing Daemon -- Route aggregation
*
* (c) 2023--2023 Igor Putovny <igor.putovny@nic.cz>
* (c) 2023 CZ.NIC, z.s.p.o.
* (c) 2023--2024 Igor Putovny <igor.putovny@nic.cz>
* (c) 2024 CZ.NIC, z.s.p.o.
*
* Can be freely distributed and used under the terms of the GNU GPL.
*/
/**
* DOC: Route aggregation
* DOC: Aggregator protocol
*
* This is an implementation of route aggregation functionality.
* It enables user to specify a set of route attributes in the configuarion file
* and then, for a given destination (net), aggregate routes with the same
* values of these attributes into a single multi-path route.
* The purpose of the aggregator protocol is to aggregate routes based on
* user-specified set of route attributes. It can be used for aggregating
* routes for a given destination (net) or for aggregating prefixes.
*
* Structure &channel contains pointer to aggregation list which is represented
* by &aggr_list_linearized. In rt_notify_aggregated(), attributes from this
* list are evaluated for every route of a given net and results are stored
* in &rte_val_list which contains pointer to this route and array of &f_val.
* Array of pointers to &rte_val_list entries is sorted using
* sort_rte_val_list(). For comparison of &f_val structures, val_compare()
* is used. Comparator function is written so that sorting is stable. If all
* attributes have the same values, routes are compared by their global IDs.
* Aggregation of routes for networks means that for each destination, routes
* with the same values of attributes will be aggregated into a single
* multi-path route. Aggregation is performed by inserting routes into a hash
* table based on values of their attributes and egenrating new routes from
* the routes in th same bucket. Buckets are represented by @aggregator_bucket,
* which contains linked list of @aggregator_route.
*
* Aggregation of prefixes aggregates a given set of prefixes into another set
* of prefixes. It offers a reduction in number of prefixes without changing
* the routing semantics.
*
* Prefix aggregation implements the ORTC (Optimal Route Table Construction)
* algorithm. This algorithm uses a binary tree representation of the routing
* table. An edge from the parent node to its left child represents bit 0, and
* an edge from the parent node to its right child represents bit 1 as the
* prefix is traversed from the most to the least significant bit. Leaf node
* of every prefix contains pointer to @aggregator_bucket where the route for
* this prefix belongs.
*
* ORTC algorithm consists of three passes through the trie.
*
* The first pass adds new nodes to the trie so that every node has either two
* or zero children. During this pass, routing information is propagated to the
* leaves.
*
* The second pass finds the most prevalent buckets by pushing information from
* the leaves up towards the root. Each node is assigned a set of potential
* buckets. If there are any common buckets among the node's children, they
* are carried to the parent node. Otherwise, all of children's buckets are
* carried to the parent node.
*
* The third pass moves down the tree, selecting a bucket for the prefix and
* removing redundant routes. The node inherits a bucket from the closest
* ancestor node that has a bucket (except for the root node). If the inherited
* bucket is a member of the node's set of potential buckets, then the node
* does not need a bucket. Otherwise, the node does need a bucket and any of
* its potential buckets can be chosen. All leaves which have not been assigned
* a bucket are removed.
*
* The algorithm works on the assumption that there is a default route, that is,
* the null prefix at the root node has a bucket. This route is created before
* the aggregation starts.
*
* Incorporation of incremental updates of routes has not been implemented yet.
* The whole trie is rebuilt and aggregation runs all over again when enough
* updates are collected. To achieve this, the aggregator uses a settle timer
* configured with two intervals, @min and @max. User can specify these
* intervals in the configuration file. After receiving an update, settle timer
* is kicked. If no update is received for interval @min or if @max interval is
* exceeded, timer triggers and refeed of the source channel is requested. When
* the refeed ends, all prefixes are inserted into the trie and aggregation
* algorithm proceeds.
*
* Memory for the aggregator is allocated from three linpools: one for buckets,
* one for routes and one for trie used in prefix aggregation. Obviously, trie
* linpool is allocated only when aggregating prefixes. Linpools are flushed
* after prefix aggregation is finished, thus destroying all data structures
* used.
*
* After sorting, &rte_val_list entries containing equivalent routes will be
* adjacent to each other. Function process_rte_list() iterates through these
* entries to identify sequences of equivalent routes. New route will be
* created for each such sequence, even if only from a single route.
* Only attributes from the aggreagation list will be set for the new route.
* New &rta is created and prepare_rta() is used to copy static and dynamic
* attributes to new &rta from &rta of the original route. New route is created
* by create_merged_rte() from new &rta and exported to the routing table.
*/
#undef LOCAL_DEBUG

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proto/aggregator/aggregator.h
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/*
* BIRD -- Aggregator Pseudoprotocol
*
* (c) 2023 Igor Putovny <igor.putovny@nic.cz>
* (c) 2023 Maria Matejka <mq@ucw.cz>
* (c) 2023 CZ.NIC z.s.p.o.
* (c) 2023--2024 Igor Putovny <igor.putovny@nic.cz>
* (c) 2023--2024 Maria Matejka <mq@ucw.cz>
* (c) 2024 CZ.NIC z.s.p.o.
*
* Can be freely distributed and used under the terms of the GNU GPL.
*