OSPF joining process

Source: Internet
Author: User

1. DOWN: no interaction activities are performed between the two parties. Ii. INIT: the user has received the hello packet from the other party, but has not received the hello packet containing the RID, that is, the user has not received the hello packet. At this time, the DR field in hello ( is completely zero because no DR is selected. How can I know whether the peer side has received my message? It can be Seen through the Neighbors Seen field. Hello package parameters: 1. Self-built RID 2, Area ID 3, hello-interval 4, hello-deadinterval 5, network mask 6, Priority 7, DR/BDR 8, neighbor RID 9, authentication information only hello the fields 2, 3, 4, 5, and 9 in the package are consistent, to form a neighbor. If there is a different discard. The ttl value of the hello packet is 1, which is sent every 10 seconds in E1. Because only two adjacent routers establish a relationship. The Hello packet does not need to be routed through the router to a non-directly connected router. 3. TWO-WAY: Both OSPF routers find their own RID in the hello packet sent from the peer end. Establish a neighbor relationship. Broadcast Networks elect DR/BDR at this stage. DR/BDR election step: Step 1: Select DR/BDR Based on the ospf router interface priority (each interface has a default priority of 1). The highest priority is DR, the second largest is BDR, and the Other is DR-Other. If the pri of A vropri is 0, the election of DR/BDR is abandoned. www.2cto.com priority: 1--255 (Serial Port has no priority by default, because it is POINT_TO_POINT by default. If you do not need to elect DR/BDR, you can view it through sh ip ospf int e0) Step 2: if the interface has the same priority, the router-id will be used to determine the DR/BDR election: the router-id is the largest DR, and the second largest is BDR, others are DR-other. Select BDR first, and then DR from DR. 4. EXSTART: In the pre-start status, the OSPF router establishes a master-slave relationship, and the master determines the serial number of the sent DD. Master-slave principle: master with a large RID. Select the master-slave reason: Before DD is transmitted, the master determines a serial number, and only the master can modify the serial number. To determine the unique DD serial number, data can be reliably obtained. Because the ip address is not reliably transmitted, confirmation + timeout retransmission is used. The first two dd packets are empty and do not contain lsa data. They are used to negotiate the serial number. At this time, I think I am the master. 5. EXCHANGE: EXCHANGE status. DRother and DR start to exchange data. The master sends the LSDB packet first. This packet is only an index (like a directory in a book) that does not contain the actual route data and also sends packets, the sender does not have one. DD package information: 1. I-bit (intial-bit) bid. If it is set to 1, only one DD package exists. If it is a sub-DD package, set 0.2 and M-bit (more-bit) to 1, indicating that the DD package is not the last one. If 0 is set, it indicates it is the last one. The DD package is sent completely. 3. If MS-bit (master/slave-bit) is set to 1, it indicates that the package is the main package, and if it is set to 0, it indicates the package from which it is sent. 4. DD sequence numberDD package serial number 6. LOADING: LOADING status. View the route data you need from the DD message, send LSR requests to send data, and send LSU to the peer. This packet contains all the required data. LSR information: www.2cto.com 1. link state type. There are a total of 11 types, but Cisco does not. Common: 1) router lsa: LID is RID. Describes the information of the router interface and the OSPF region interface, which is only flooding in the region. 2) network lsa: the LID is the IP address of the DR interface connecting to the region. The router information of the region is described when a DR is generated. Is to ensure that only one network lsa is generated in the broadcast network.
3) network summary lsa: LID is the destination network number. It is generated by an API and describes networks in other regions it knows. 4) asbr las: the LID is the RID of asba. It is generated by ASBR and describes its location so that other routers can find and reach it. 5) as external lsa: LID is the external network number. The route information generated by ASBR to the external network. 6) nssa external lsa: the LID is the external network number. This is generated by ASBR and describes the direct connection of The nssa region to external routes. It is included in lsa 5th so that it can be distributed to regions that support lsa 5th. 2. link id: the link id varies with the lsa. 3. advertising router: Send the RID of lsa.
LSU information: Data Link update package. LAS is included in LSU. LSA (Data Link announcement, LSA is included in LSU) Propagation update Rule: Step 1: If the router has never received this LSA, then the router adds it to LSDB, and forward/flood the LSA. Step 2: If the vro receives the LSA: 2-1 that describes the same network: If the serial number of the LSA is the same as its own, the LSA is discarded. 2-2: If the serial number of the LSA is the same as its own update, it is the same step. 2-3: If the serial number of the LSA is older than its own, it will send its new LSA to the source. Www.2cto.com 7. FULL: After receiving the LSU message, the system sends a confirmation message to complete the status. When DR/BDR exists, the DR does not send LSAck after receiving LSU. Because when DR flooding LSU in the region, when the send router listens to the LSA, it is considered as a confirmation. When no DR/BDR exists, the receiving router sends LSAck. When the status is full, all the routes in the region have the same LSDB. The Full status is the normal connection status of DR/BDR and DRother. While the two-way state is the normal state of the connection between DRother from the INIT--LOADING is the first time the router information exchange occurs, after the full, if there is a route change, only after lsu is sent to complete the full state. The router uses the spf algorithm to calculate the optimal path to a known network based on its own root. Author flying

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