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Introdution into OSPF.

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Ondrej Filip 2000-06-07 20:30:27 +00:00
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proto/ospf/ospf.c
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/*
* BIRD -- OSPF
*
* (c) 1999 Ondrej Filip <feela@network.cz>
* (c) 1999-2000 Ondrej Filip <feela@network.cz>
*
* Can be freely distributed and used under the terms of the GNU GPL.
*/
/**
* DOC: Open Shortest Path First (OSPF)
*
* As OSPF protocol is quite complicated and complex implemenation is
* split into many files. In |ospf.c| you can find mostly interfaces
* for communication with nest. (E.g. reconfiguration hooks, shutdown
* and inicialisation and so on.) In |packet.c| you can find various
* functions for sending and receiving generic OSPF packet. There are
* also routins for autentications, checksumming. |Iface.c| contains
* interface state machine, allocation and deallocation of OSPF's
* interface data structures. |Neighbor.c| includes neighbor state
* machine and function for election of Designed Router and Backup
* Designed router. In |hello.c| there are routines for sending
* and receiving hello packets as well as functions for maintaining
* wait times and inactivity timer. |Lsreq.c|, |lsack.c|, |dbdes.c|
* contains functions for sending and receiving link-state request,
* link-state acknoledge and database description respectively.
* In |lsupd.c| there are function for sending and receiving
* link-state updates and also flooding algoritmus. |Topology.c| is
* a place where routins for searching LSAs in link-state database,
* adding and deleting them, there are also functions for originating
* various types of LSA. (router lsa, net lsa, external lsa) |Rt.c|
* contains routins for calculating of routing table.
*
* Just one instance of protocol is able to hold LSA databases for
* multiple OSPF areas and exhange routing information between
* multiple neighbors and calculate routing tables. The core
* structure is &proto_ospf, to which multiple &ospf_area and
* &ospf_iface are connected. To &ospf_area is connected
* &top_hash_graph, which is a dynamic hashing structure that
* describes link-state database. It allows fast search, adding
* and deleting. Every area has it's own area_disp() that is
* responsible for late originating of router LSA, calcutating
* of routing table and it also ages and flushes LSA database. This
* function is called in regular intervals.
* To every &ospf_iface is connected one or more
* &ospf_neighbors. This structure contains many timers and queues
* for building adjacency and exchange routing messages.
*
* BIRD's OSPF implementation respects RFC2328 in every detail but
* some of inner function differs. RFC recommends to make a snapshot
* of link-state database when new adjacency is building and send
* database description packets based on information of this
* snapshot. The database can be quite large in some networks so
* I rather walk through &slist structure which allows me to
* continue even if actual LSA I worked on is deleted. New
* LSA are added to the tail of this slist.
*
* I also don't build another, new routing table besides the old
* one because nest helps me. I simply flush all calculated and
* deleted routes into nest's routing table. It's simplyfies
* this process and spares memory.
*/
#include "ospf.h"
static int