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The patch adds support for channels, structures connecting protocols and tables and handling most interactions between them. The documentation is missing yet.
75 lines
3.6 KiB
Plaintext
75 lines
3.6 KiB
Plaintext
<!--
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BIRD Programmer's Guide: Protocols
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(c) 2000 Martin Mares <mj@ucw.cz>
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-->
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<sect>Routing protocols
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<sect1>Introduction
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<p>The routing protocols are the bird's heart and a fine amount of code
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is dedicated to their management and for providing support functions to them.
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(-: Actually, this is the reason why the directory with sources of the core
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code is called <tt/nest/ :-).
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<p>When talking about protocols, one need to distinguish between <em/protocols/
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and protocol <em/instances/. A protocol exists exactly once, not depending on whether
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it's configured or not and it can have an arbitrary number of instances corresponding
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to its "incarnations" requested by the configuration file. Each instance is completely
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autonomous, has its own configuration, its own status, its own set of routes and its
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own set of interfaces it works on.
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<p>A protocol is represented by a <struct/protocol/ structure containing all the basic
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information (protocol name, default settings and pointers to most of the protocol
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hooks). All these structures are linked in the <param/protocol_list/ list.
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<p>Each instance has its own <struct/proto/ structure describing all its properties: protocol
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type, configuration, a resource pool where all resources belonging to the instance
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live, various protocol attributes (take a look at the declaration of <struct/proto/ in
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<tt/protocol.h/), protocol states (see below for what do they mean), connections
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to routing tables, filters attached to the protocol
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and finally a set of pointers to the rest of protocol hooks (they
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are the same for all instances of the protocol, but in order to avoid extra
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indirections when calling the hooks from the fast path, they are stored directly
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in <struct/proto/). The instance is always linked in both the global instance list
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(<param/proto_list/) and a per-status list (either <param/active_proto_list/ for
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running protocols, <param/initial_proto_list/ for protocols being initialized or
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<param/flush_proto_list/ when the protocol is being shut down).
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<p>The protocol hooks are described in the next chapter, for more information about
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configuration of protocols, please refer to the configuration chapter and also
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to the description of the <func/proto_commit/ function.
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<sect1>Protocol states
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<p>As startup and shutdown of each protocol are complex processes which can be affected
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by lots of external events (user's actions, reconfigurations, behavior of neighboring routers etc.),
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we have decided to supervise them by a pair of simple state machines -- the protocol
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state machine and a core state machine.
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<p>The <em/protocol state machine/ corresponds to internal state of the protocol
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and the protocol can alter its state whenever it wants to. There are
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the following states:
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<descrip>
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<tag/PS_DOWN/ The protocol is down and waits for being woken up by calling its
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start() hook.
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<tag/PS_START/ The protocol is waiting for connection with the rest of the
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network. It's active, it has resources allocated, but it still doesn't want
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any routes since it doesn't know what to do with them.
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<tag/PS_UP/ The protocol is up and running. It communicates with the core,
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delivers routes to tables and wants to hear announcement about route changes.
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<tag/PS_STOP/ The protocol has been shut down (either by being asked by the
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core code to do so or due to having encountered a protocol error).
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</descrip>
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<p>Unless the protocol is in the <tt/PS_DOWN/ state, it can decide to change
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its state by calling the <func/proto_notify_state/ function.
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<p>At any time, the core code can ask the protocol to shut itself down by calling its stop() hook.
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<sect1>Functions of the protocol module
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<p>The protocol module provides the following functions:
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