Introduction to OSPF protocol in Huawei Technology

1.1. OSPF getting started

You can set the entire network

(An autonomous system as) as a kingdom, which can be divided into several areas (areas). Now let's look at a person in the region (root of your machine) how to get 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.
They will yell, so that you know which people are around, and you have established a neighbor relationship with them. Of course, they also have a neighbor relationship.
　　
Among you, the most prestigious (Priority 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 ".
　　
You have to use the leader to know more messages. First, you can communicate with each other.

Message: he tells you the names of all maps he knows. You will also tell him the names you know. Of course, you may have only one point. (Database description database description packet)
　　
You find that you have something missing or newer than you in the name list. You will ask him for more detailed information. He found that your name list contains what he needs, he will also ask you for new information. (Link State request connection status request message)
　　
Of course, you do not hesitate to send a detailed copy to the other party. (Link state Update Connection status update packets)
　　
　
After receiving the map, I acknowledge that I have received it. (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 find the map to pick a path to all the places nearest (Shortest Path), as a table (Routing
Table route table), of course, you will find the nearest path to the destination after querying this table. 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 ). You will also have two groups of people (two CIDR blocks in the same region ),
Tell you the map of another group of people, of course, will also leak the map of your group (but 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
Come in. 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.
　　
Some people, as boundary router Autonomous System (VBR)

), They know the path of "Going Abroad" (as external route autonomous system external Routing), of course they will introduce these secrets to the public (import), through information transmission, now you have a complete map of the world.
　　
　
OSPF marks the shortest path as follows: for a destination, first consider whether there is a path from the same area to the destination (Intra
In the Area). If yes, take one of them (the minimum cost) and write it into your table, this destination may be for a specific person in this group or another group.
You will not consider routing in a region. It is better to deal with your own people (in the same region) than with outsiders (in other regions). If you do not have a route in this region, you have to pass through other areas (between areas), you just need
Find the nearest destination. If you find that your destination is abroad, you can only mark it on your table first. When do you expect the kingdom to expand there, you can mark it on the domestic map.
　　
OSPF is like this. It just gives you a "World Map" and marks the Shortest Path on it.
　　
　　1.2. Background

In TCP/IP protocol, it is very important to find a route from one computer to another.
　　
1. Determine whether a path can be found.
　　
2. Find a short path after finding the path (minimum time consumed)
　　
3. Do not loop when finding a path
　　
4. It is better to be able to dynamically handle route changes, such as up or down of interfaces, changes in time consumption, and network
Structure Change.
　　
The OSPF proposed by Internet Engineering Task Force in 1988 is a link-based dynamic routing protocol,
　　
[Basic ideas of the Protocol

As follows: each OSPF router in the Autonomous System
Accept
Each set of interfaces/adjacent information is called a link state. The flooding algorithm is used to broadcast its own link state in the entire system, so that a synchronized Link State database is maintained within the entire system.
A database, the router calculates a shortest path tree with its own root node and other network nodes as its leaves, so as to calculate the optimal route that it can reach the system.]
　　
OSPF is a type of interior gateway protocol (Internal Gateway
Protocol IGP), which processes the route table information of the router network in an autonomous system.
　　
　　1.3. Terms and Basic Concepts

OSPF routing protocol terminology:
OSPF Routing Protocol: Open Shortest Path First Shortest Path Priority Protocol
　　
Router (router): The layer-3 IP packet switch. It was also called a gateway in the IP document.
　　
Autonomous System: A group of routers exchange routing information through the same routing protocol,
　　
As region: the unit of autonomous system. An autonomous system can be divided into multiple regions.
　　
Area ID: The 32-bit identifier of the autonomous system.
　　
Internal Gateway Protocol: a route that runs on a vro of an autonomous system
　　
Each autonomous system has a separate IGP. Different autonomous systems may
　　
Run different IGP. OSPF is a type of internal gateway protocol.
　　
Router ID (router ID): A 32-bit label for each router running OSPF, in the Autonomous System
　　
Unified is unique

Of
　　
Network: In this sense, it is an IP Network/subnet/supernetwork, which may be marked with multiple composite IP addresses.
　　
Address subnets. We regard them as isolated networks. Point-to-Point physical networks are special cases.
　　
It is just treated as a simple network, no matter how you specify the IP number for them.
　　
Network mask (network mask): A 32-bit number indicates the IP address range of the IP network.
　　
For example, the mask of a Class C network is 0xfffff00, which is written as limit 255.0 in text.
　　
Point-to-Point Network: a network composed of a pair of routers, such as
　　
56 KB string line connection
　　
Broadcast Network: The network supports many (more than two) routers. All have the ability to send address information to all connections
　　
The (broadcast) neighbor router on the connected router is dynamically discovered by the OSPF Hello protocol.
　　
The broadcast capability can be used for larger applications. If it exists, each pair of routers on it is assumed to be able to communicate with each other.
　　
Directly Connected. Ethernet is an example of a broadcast network.
　　
Non-broadcast network: The network supports many (more than two) routers, but it does not have broadcast capabilities. Neighboring nodes are also maintained through OSPF hello packets. However, due to the broadcast capability, some neighbors need to be configured to discover the network, OSPF packets are also transmitted between neighbors. X.25 is an example.
　　
OSPF can run on two non-broadcast networks. One is non-broadcast multi-access (nbma), which is similar to OSPF operation on the broadcast network, and the other is point-to-point, A set of multiple point-to-point connections. The identification of non-broadcast networks depends on the network operation mode.
　　
Interface: an interface is a network connection between a vro and it. An interface has its status information and can be obtained through the underlying protocol or the routing protocol itself. Each interface has a unique IP address and mask (unless it is an unlabeled point-to-point connection), and an interface sometimes refers to a connection.
　　
Neighbor: The two routers have interfaces connected to a common network, and the neighbor relationship is maintained through the OSPF Hello protocol (usually dynamic ).
　　
Adjacency: the relationship established between neighbors for the exchange of routes. Not every neighbor is adjacent.
　　
Link State advertise: describes the data unit of a local router or network. For a vro, it describes the interface status and adjacent status of the vro, the first connection status is sent to the entire routing domain.

All connection status transfer forms the Protocol connection status database, which is used globally, abbreviated as LSA
　　
Link State database: All connection status transfers constitute a connection state database.
　　
Stub network: Only one interface is connected to the external network. For example, a PPP can be viewed as a stub network.
　　
Backbone area: vbrs in all regions and routes between them form backbone areas.
　　
　
As external route: refers to the routes obtained from non-OSPF protocols, such as BGP (Border Gateway Protocol) and rip (Routing
Information
Protocol), the system static configuration routing, etc., the System Static Routing is obtained from the configuration, other protocol routing is obtained through the introduction operation, the external routing is determined by the user.
　　
Route: the connection path between two nodes.
　　
Routing table: There is a route to each destination. Such a table is called a route table.
　　
Basic concepts:
OSPF regards the entire network (subnet on the Internet or other types of networks) as an autonomous system ()
　　
In each as, several physically adjacent routers (routers) and networks form an area. These areas are generally non-intersecting and divide the entire.
　　
Is an example of a typical Autonomous System Division:

Rxx represents the router, N * represents the network,
　　
1. R1, R2, R3, R4, and N1 are composed of Region 1, R3, and R4 are regional border routers (ABR)
　　
2. R7, R8, R10, N2, and N3 are composed of Region 2, R7, R10, and R11)
　　
3. r9.r11, R12, N4 composition Area 3, R11 is the Regional Border Router (ABR)
　　
4. All regional edge nodes (R3, R4, R7, R10, R11) and R5 and R6 form a backbone area (backbone area)

 

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