Ospfb notes - five messages [ultra detailed] [Hello message, DD message, LSR message, LSU message, lsack message]

Catalog

Hello message

DD message [ Database description message ]

LSR message

LSU message

LSAck message

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We have learned from the above ospf Message header of 【 link ：OSPF Header message https://blog.csdn.net/weixin_58757687/article/details/122896057】, It is worth noting that ： all ospf Messages carry this ospf Head .

The topology of this experiment is as follows ：

Once the interface is turned on ospf Interface 【 example ：R1 On network192.168.1.0 It opens. R1 Of G0/0/0 Interface ospf function 】 Start periodic release Hello message , Used to find neighbors on the direct link . The interface of the router receives from other routers Hello When the message

Hello message

Hello The message has two functions ：1. Used to find neighbors . 2. Maintaining neighborhood relations .

Now grab just one Hello Message to understand Hello message The format of ：

Subnet mask ： This field is for sending the Hello Interface subnet mask of the message , Two routers directly connected to Ethernet 【 Such as two directly connected routers 】 The subnet mask must be the same to establish a neighbor , Otherwise, ignore the Hello message .

Hello interval ：Hello Flooding period of message .

optional ： altogether 8 position , Each bit represents the sending of the Hello A feature or feature supported by a router .

Router priority ： It's also called DR priority , The default value is 1【 The higher priority is DR, Next is BDR】. It can be done by 【   [Huawei-GigabitEthernet0/0/0]     ospf dr-priority  0~255  】 To modify the priority . Be careful ： When the priority is set to 0 when , This port will not participate in DB and BDR The election .

Router failure time ： The neighbor router is set to Down[ invalid ] Waiting time before , The default is Hello Spaced 4 times .

DR The interface of IP： In this network DR Interface IP, If 0.0.0.0 It means there is no DR or DR Not elected .

BDR The interface of IP： In this network BDR Interface IP, If 0.0.0.0 It means there is no BDR or BDR Not elected .

neighbor Router-ID： The router has found all Effective neighbors [ That is, neighbors who have established neighborhood relations with each other { At this time, the lowest position 2-way state }, About ospf Subsequent status updates will be introduced in detail .]

DD message [ Database description message ]

DD The message can have one or more , basis LSA To determine the number of .

LSA： Link status notification , stay ospf Is used to describe your own interface status ,cost[ It's also called ： measurements 、 expenses ], Neighbor relation message .

DD The message describes LSDB[ Link state database , What is stored is all LSA Information ] Of LSA Header information rather than complete LSA.

Now grab a random DD message ：

  Maximum transmission unit ： With bit In units of , Controlling the same message requires fragment transmission 【 Default is 0】.

optional ： The router supports ospf Function or characteristic .

I position ： If the bit is 1 It means that we should DD Messages are used for negotiation Mater/Slave[ Lord / from ]{ link ：DD In the message [ Lord / from ] Router election https://blog.csdn.net/weixin_58757687/article/details/122951880}. by 0 It means that the election has been completed .

M position ： If there is still DD The message is 1, If it's the last one DD The message is 0.

MS position ： If it is the main route, it is 1, The slave route is 0.

DD Serial number ： This field is used to guarantee DD Order in message transmission . To protect DD Effectiveness of message transmission process ,DD The message will be sent by Mater{ Main route } To transmit to Slave{ From routing }, also DD The sequence is determined by the master route . The whole process is like this ： First of all Hello Packet discovery and neighbor relationship with neighboring routes , Re release Empty DD The message is used for election Mater/Slave[ here DD Serial numbers can be different ], The election is over Mater/Slave after Release with LSA Of DD message [ here DD The serial number of the message is from Mater decision ,Slave Can only be used Mater The serial number sent is used as its own serial number to issue the serial number with LSA Of DD Send a message to Mater Router , also Slave The router receives the next message from Mater It's from DD The message will be released again DD Send a message to Mater.]

LSA Head ： Used to describe the link state database LSA Head , There can be one or more .

LSR message

LSR【 Link status request message 】： Used to request complete LSA{ Be careful ： Only ask for what you don't have LSA}.

  Link state type ： Common are 7 The two types are ：type-1 Router LSA ,type=2 Network LSA ,type-3 Network Summary LSA , type-4 ASBR Summary LSA, type-5 AS External LSA, type-6 Group Membership LSA,type -7 NSSA LSA. # Subsequent updates , If updated, I will put the link on the top of the comment area .

Link status identification ：LSA identification .   # Subsequent updates , If updated, I will put the link on the top of the comment area .

Notification routing ： Describe the generation of this LSR The router Router-ID.

LSU message

LSU The message contains complete LSA Information , To reply to LSR message . And when the router perceives that the network has changed, it will also flood LSU. stay MA[ Multiple access to the network ,MA link ：MA Network and two OSPF Multicast address https://blog.csdn.net/weixin_58757687/article/details/122951880]

Be careful ： Not DR/BDR The router LSU The message is sent to 224.0.0.6 Address of the , and DR After receiving this message, it will be sent to 224.0.0.5[ be-all OSPF Router ]. This will greatly reduce the network expenses , It is conducive to the optimization of the network .

LSU The message is as follows ：

# LSA The message will be introduced in detail later , The update will be posted in the comment area .

LSAck message

LSAck： Link status acknowledgement message , Used to confirm LSU message . In order to protect every LSA Can be up to , need LSAck Come on, what you receive every day LSA Confirm .

LSAck What is included is what is to be confirmed LSA Header information { Every LSA The length of the head is 20byte}.

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