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diff --git a/nest/proto.sgml b/nest/proto.sgml new file mode 100644 index 0000000..45ef88d --- /dev/null +++ b/nest/proto.sgml @@ -0,0 +1,91 @@ +<!-- + BIRD Programmer's Guide: Protocols + + (c) 2000 Martin Mares <mj@ucw.cz> +--> + +<sect>Routing protocols + +<sect1>Introduction + +<p>The routing protocols are the BIRD's heart and a fine amount of code +is dedicated to their management and for providing support functions to them. +(-: Actually, this is the reason why the directory with sources of the core +code is called <tt/nest/ :-). + +<p>When talking about protocols, one need to distinguish between <em/protocols/ +and protocol <em/instances/. A protocol exists exactly once, not depending on whether +it's configured on not and it can have an arbitrary number of instances corresponding +to its "incarnations" requested by the configuration file. Each instance is completely +autonomous, has its own configuration, its own status, its own set of routes and its +own set of interfaces it works on. + +<p>A protocol is represented by a <struct/protocol/ structure containing all the basic +information (protocol name, default settings and pointers to most of the protocol +hooks). All these structures are linked in the <param/protocol_list/ list. + +<p>Each instance has its own <struct/proto/ structure describing all its properties: protocol +type, configuration, a resource pool where all resources belonging to the instance +live, various protocol attributes (take a look at the declaration of <struct/proto/ in +<tt/protocol.h/), protocol states (see below for what do they mean), connections +to routing tables, filters attached to the protocol +and finally a set of pointers to the rest of protocol hooks (they +are the same for all instances of the protocol, but in order to avoid extra +indirections when calling the hooks from the fast path, they are stored directly +in <struct/proto/). The instance is always linked in both the global instance list +(<param/proto_list/) and a per-status list (either <param/active_proto_list/ for +running protocols, <param/initial_proto_list/ for protocols being initialized or +<param/flush_proto_list/ when the protocol is being shut down). + +<p>The protocol hooks are described in the next chapter, for more information about +configuration of protocols, please refer to the configuration chapter and also +to the description of the <func/proto_commit/ function. + +<sect1>Protocol states + +<p>As startup and shutdown of each protocol are complex processes which can be affected +by lots of external events (user's actions, reconfigurations, behaviour of neighboring routers etc.), +we have decided to supervise them by a pair of simple state machines -- the protocol +state machine and a core state machine. + +<p>The <em/protocol state machine/ corresponds to internal state of the protocol +and the protocol can alter its state whenever it wants to. There exist +the following states: + +<descrip> + <tag/PS_DOWN/ The protocol is down and waits for being woken up by calling its + start() hook. + <tag/PS_START/ The protocol is waiting for connection with the rest of the + network. It's active, it has resources allocated, but it still doesn't want + any routes since it doesn't know what to do with them. + <tag/PS_UP/ The protocol is up and running. It communicates with the core, + delivers routes to tables and wants to hear announcement about route changes. + <tag/PS_STOP/ The protocol has been shut down (either by being asked by the + core code to do so or due to having encountered a protocol error). +</descrip> + +<p>Unless the protocol is in the <tt/PS_DOWN/ state, it can decide to change +its state by calling the <func/proto_notify_state/ function. + +<p>At any time, the core code can ask the protocol to shut down by calling its stop() hook. + +<p>The <em/core state machine/ takes care of the core view of protocol state. +The states are traversed according to changes of the protocol state machine, but +sometimes the transitions are delayed if the core needs to finish some actions +(for example sending of new routes to the protocol) before proceeding to the +new state. There exist the following core states: + +<descrip> + <tag/FS_HUNGRY/ The protocol is down, it doesn't have any routes and + doesn't want them. + <tag/FS_FEEDING/ The protocol has reached the <tt/PS_UP/ state, but + we are still busy sending the initial set of routes to it. + <tag/FS_HAPPY/ The protocol is up and has complete routing information. + <tag/FS_FLUSHING/ The protocol is shutting down (it's in either <tt/PS_STOP/ + or <tt/PS_DOWN/ state) and we're flushing all of its routes from the + routing tables. +</descrip> + +<sect1>Functions of the protocol module + +<p>The protocol module provides the following functions: |