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/*
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* BIRD Internet Routing Daemon -- Route aggregation
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*
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* (c) 2023--2023 Igor Putovny <igor.putovny@nic.cz>
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* (c) 2023 CZ.NIC, z.s.p.o.
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* (c) 2023--2024 Igor Putovny <igor.putovny@nic.cz>
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* (c) 2024 CZ.NIC, z.s.p.o.
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*
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* Can be freely distributed and used under the terms of the GNU GPL.
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*/
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/**
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* DOC: Route aggregation
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* DOC: Aggregator protocol
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*
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* This is an implementation of route aggregation functionality.
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* It enables user to specify a set of route attributes in the configuarion file
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* and then, for a given destination (net), aggregate routes with the same
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* values of these attributes into a single multi-path route.
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* The purpose of the aggregator protocol is to aggregate routes based on
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* user-specified set of route attributes. It can be used for aggregating
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* routes for a given destination (net) or for aggregating prefixes.
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*
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* Structure &channel contains pointer to aggregation list which is represented
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* by &aggr_list_linearized. In rt_notify_aggregated(), attributes from this
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* list are evaluated for every route of a given net and results are stored
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* in &rte_val_list which contains pointer to this route and array of &f_val.
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* Array of pointers to &rte_val_list entries is sorted using
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* sort_rte_val_list(). For comparison of &f_val structures, val_compare()
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* is used. Comparator function is written so that sorting is stable. If all
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* attributes have the same values, routes are compared by their global IDs.
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* Aggregation of routes for networks means that for each destination, routes
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* with the same values of attributes will be aggregated into a single
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* multi-path route. Aggregation is performed by inserting routes into a hash
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* table based on values of their attributes and egenrating new routes from
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* the routes in th same bucket. Buckets are represented by @aggregator_bucket,
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* which contains linked list of @aggregator_route.
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*
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* Aggregation of prefixes aggregates a given set of prefixes into another set
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* of prefixes. It offers a reduction in number of prefixes without changing
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* the routing semantics.
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*
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* Prefix aggregation implements the ORTC (Optimal Route Table Construction)
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* algorithm. This algorithm uses a binary tree representation of the routing
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* table. An edge from the parent node to its left child represents bit 0, and
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* an edge from the parent node to its right child represents bit 1 as the
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* prefix is traversed from the most to the least significant bit. Leaf node
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* of every prefix contains pointer to @aggregator_bucket where the route for
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* this prefix belongs.
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*
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* ORTC algorithm consists of three passes through the trie.
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*
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* The first pass adds new nodes to the trie so that every node has either two
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* or zero children. During this pass, routing information is propagated to the
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* leaves.
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*
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* The second pass finds the most prevalent buckets by pushing information from
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* the leaves up towards the root. Each node is assigned a set of potential
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* buckets. If there are any common buckets among the node's children, they
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* are carried to the parent node. Otherwise, all of children's buckets are
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* carried to the parent node.
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*
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* The third pass moves down the tree, selecting a bucket for the prefix and
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* removing redundant routes. The node inherits a bucket from the closest
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* ancestor node that has a bucket (except for the root node). If the inherited
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* bucket is a member of the node's set of potential buckets, then the node
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* does not need a bucket. Otherwise, the node does need a bucket and any of
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* its potential buckets can be chosen. All leaves which have not been assigned
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* a bucket are removed.
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*
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* The algorithm works on the assumption that there is a default route, that is,
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* the null prefix at the root node has a bucket. This route is created before
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* the aggregation starts.
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*
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* Incorporation of incremental updates of routes has not been implemented yet.
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* The whole trie is rebuilt and aggregation runs all over again when enough
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* updates are collected. To achieve this, the aggregator uses a settle timer
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* configured with two intervals, @min and @max. User can specify these
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* intervals in the configuration file. After receiving an update, settle timer
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* is kicked. If no update is received for interval @min or if @max interval is
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* exceeded, timer triggers and refeed of the source channel is requested. When
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* the refeed ends, all prefixes are inserted into the trie and aggregation
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* algorithm proceeds.
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*
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* Memory for the aggregator is allocated from three linpools: one for buckets,
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* one for routes and one for trie used in prefix aggregation. Obviously, trie
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* linpool is allocated only when aggregating prefixes. Linpools are flushed
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* after prefix aggregation is finished, thus destroying all data structures
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* used.
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*
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* After sorting, &rte_val_list entries containing equivalent routes will be
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* adjacent to each other. Function process_rte_list() iterates through these
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* entries to identify sequences of equivalent routes. New route will be
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* created for each such sequence, even if only from a single route.
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* Only attributes from the aggreagation list will be set for the new route.
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* New &rta is created and prepare_rta() is used to copy static and dynamic
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* attributes to new &rta from &rta of the original route. New route is created
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* by create_merged_rte() from new &rta and exported to the routing table.
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*/
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#undef LOCAL_DEBUG
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@ -1,9 +1,9 @@
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/*
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* BIRD -- Aggregator Pseudoprotocol
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*
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* (c) 2023 Igor Putovny <igor.putovny@nic.cz>
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* (c) 2023 Maria Matejka <mq@ucw.cz>
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* (c) 2023 CZ.NIC z.s.p.o.
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* (c) 2023--2024 Igor Putovny <igor.putovny@nic.cz>
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* (c) 2023--2024 Maria Matejka <mq@ucw.cz>
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* (c) 2024 CZ.NIC z.s.p.o.
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*
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* Can be freely distributed and used under the terms of the GNU GPL.
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*
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