Learn OSPF like watching a movie

Like watching a movie, OSPF can regard the entire network (AS) AS a kingdom, which can be divided into several areas ), now let's take a look at how a person (root of your machine) in the region gets a routing table. First, you need to establish basic connections with people around you (for example, 129.102 in the same network segment. You yell, "I'm here !" (Send a HELLO message), so people around you know that you exist, and they will yell, so that you know who is around, and you have established a neighbor (neighbor) with them) relationship, of course, they also have a neighbor relationship. Among you, the most prestigious (Priority) People will be recommended as leaders (Designated Router) and you will be associated with adjacency ), it will establish a single-line connection with you, instead of having too many interactions with other neighbors. He will say, "In that case, the street is too crowded ". Www.2cto.com
You have to use the leader to know more messages. First, you can exchange messages. He tells you the names of all maps he knows, you will also tell him the place name you know. Of course, you may have only one point. (Database Deion Database description packet) If you find that you have something missing or newer than you in the name list, you will ask him for more detailed information, he finds that there is something he needs in your table, and he will ask you for new information. (Link State Request connection status Request message) Of course, you do not hesitate to send a detailed information to the other party. (Link State Update Connection status Update message) After receiving the map, each other will acknowledge receipt. (Link State Ack connection status Response Message) Now, you have done your best to get a map (Link State DataBase connection status DataBase ), you can search for a map to pick a shortest path closest to all locations and record it as a table (routing table route table ), of course, you will find the nearest path to your destination by checking this form later. The map should also be collected. In case a certain path on the table fails, you can use the graph to find a new path.
In fact, there are only a group of people around you who need to know the news from outside through the leaders. Because your map is the same as that of the leader, we assume that you are the leader and you are going to draw a map of the world. You command all the people to inform you of the news, you can know any small movement of your group (event Events ). There will also be two groups of people under you (two CIDR blocks in the same region). He will tell you the map of another group of people and, of course, leak the map of your group, (However, it doesn't matter ). In this way, you will know the map of the entire area (we will try our best if you don't know it ). By constantly switching maps, people in the whole district now have the same map. People living on the border of the district are obliged to map the area (precise to every group of people) send the information to another region. The King will name these borders as backbone areas ). With the unremitting efforts of key people, you now have a clear understanding of the map of the entire country. Www.2cto.com some people (AS Boundary Router Self-Governing System border Router) know some "Going Abroad" (AS External route autonomous system External route, of course, they will introduce these secrets to the public (import) through information transmission. Now, you already have a complete "World Map.
OSPF marks the shortest path as follows: for a destination, first, consider whether there is a path from the same region to the destination (in the intra area). If yes, take one of the items closest to you (with the minimum cost) and write it into your table. This destination may be for a specific person in this group or another group, for routes that pass through other regions, you will not consider it. It is better to deal with yourself (in the same region) than with outsiders (in other regions). If there is no route in this region, you have to go through other regions (between regions). You only need to find the nearest one on the map. If you find that the destination is abroad, you can only mark it on your table first, and then you can mark it on the map of China when you expect the kingdom to expand there. OSPF is like this. I will give you a "World Map" and mark the Shortest Path on it. That's all.