HCNP the principle and configuration of OSPF protocol for learning Notes 4-adjacency relationship establishment and LSDB synchronization

After entering the Exstart state, the broadcast and NBMA networks have to wait 4 times times the hello time to determine the DR and BDR. Then the adjacency relation is established, and the interactive link state is advertised to achieve the consistency by using LSDB, and then the calculation and generation of the routing table is completed.

1 Change of the state

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ExStart: The master-slave relationship is formed in this state (router ID is the main). The purpose of determining the master-slave relationship is to determine the serial number in the DD Exchange process (LS Sequence numbers, which are described later)to ensure the reliability of the DD packet transmission, and the initial DD serial number is determined in this state. after the neighbor state becomes this state, the router begins sending a DD message to the neighbor. The DD message sent in this state does not contain a link state description, but only determines the master-slave relationship.

Exchange: in this state, routers send each other a DD message containing a summary of the link status information, describing the contents of the local LSDB .

Loading: send the LS request message to the LSA, sending the LS Update notification LSA.

Full : The LSDB of the two router is already synchronized.

That is: To determine the master-slave relationship, interactive dd-> send each other ls R and LS u-> to achieve synchronization, which means that the ultimate goal of establishing adjacency relationship is to achieve LSDB synchronization.

The following highlights the transformation process of two States

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From more than the main one DD package, confirm the master's last DD package, ensure absolute reliability

i-bit:1 is the first DD package

m bit: more bit 1 refers to the DD packet, 0 indicates the last DD packet

MS bit: main Master 1, 0 is from

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1. After the neighbor status becomes loading,RTA begins sending the LS request message to RTB, requesting the link state information that was discovered through the DD message in Exchange state and not in the local LSDB.

2. After an LS request message is received by RTB, the LS update message is sent to RTA, which contains the details of the requested link state in the LS update message.

3. RTA sends LS ACK messages to RTB to ensure the reliability of the information transmission. The LS ACK message is used for flooding the acknowledgment of the received LSA. the neighbor state becomes full, indicating that the complete adjacency state is reached.

By grasping the packet, the delivery of the actual package is cross-

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Example: This part of the content, the proposed actual capture packet analysis, the attachment content can be opened by the Huawei Simulator ENSP, and grab packet analysis

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HCNP the principle and configuration of OSPF protocol for learning Notes 4-adjacency relationship establishment and LSDB synchronization