[hcip] OSPF relationship establishment

Catalog

Neighborhood building

The election DR  and BDR

Establish a master-slave relationship

Adjacency relationship establishment

Interaction LSA

OSPF  Supported network types

OSPF  Multicast address

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OSPF  Message type

（1）Hello  message ： Used to establish neighborhoods

（2）DD  message ： For interactive LSA  Summary information of

（3）LSR  message ： Used to send a message LSA

（4）LSU  message ： Used for sending LSA  Details of

（5）LSACK  message ： Used to check the received LSA  Confirm

Neighborhood building

 （1） Turn on OSPF  The neighbor states in the device neighbor table of are initially Down

（2）A  towards B  send out Hello  message , Carry your own Router ID

（3）B  Upon receipt A  Put it in the neighbor list and put A  The status of is set to  init, Reply again Hello  message , Carry yourself and A  Of Router ID

（4）A  Upon receipt B  In your neighbor list and directly put B  The status in the neighbor table is set to 2-Way, Again to B  reply Hello  message , Carry yourself and B  Of Router ID

（5）B  After receipt of , take A  The status in the neighbor table is set to 2-Way

The election DR  and BDR

After building a neighborhood relationship, there are 40  Second election DR  and BDR, Elected DR  and BDR  Can't be forcibly occupied

Router ID：

If not specified Router ID, Then the global Router ID, It will not change automatically after use .

overall situation Router ID：

Because every routing protocol needs Router ID, So use   overall situation Router ID  As the default of Routing Protocol Router ID.

overall situation Router ID  Election rules ： The first device configuration IP  Address .

Establish a master-slave relationship

Used to initialize the link state database

1、DRother  and DR  The state between two is determined by 2-Way  To ExStart  And send each other DD  message （ Content is empty , The serial number is random ,Options  All set ）.

2、Router-ID  Small become slave devices , Lose the power to generate serial numbers （ Serial number is the serial number of the message sent by the main device ）, The state is set to ExChange  And the reply DD  message （ Serial number is the main equipment serial number ,I  by 1,MS  by 0）.

3、 After the main equipment is received , Because the serial number is the serial number of the last message , Then confirm that the other party has received the data and become a slave device （ Implicit confirmation ）, Change your status to ExChange, Continue to send message interaction data （ Serial number in sequence +1,）.

4、 The adjacency relationship is established , The status of both parties changes to Loading, And start interacting LSA.

After receiving the message from the device , If the message serial number has been +1, Then confirm that the other party has received the data sent by itself （ Implicit confirmation ）, When interacting with data again , The serial number is the serial number of the opposite party .

When the master device receives the slave device M  In place DD  When the message （ Indicates that the slave device still has data to send ）, Because the slave device cannot generate serial numbers , At this time, the master device will send an empty DD  The message provides the serial number to the slave device .

Adjacency relationship establishment

All non DR  Hui He DR、BDR  Establish adjacency between （FULL）,DROther  They will only establish a neighbor relationship （2-Way）, No interaction LSA.

Interaction LSA

  LSDB  Interaction principle ： Interaction itself does not LSA, And use new LSA, Replace old LSA.

1、 According to the other party's LSDB  Send... To the other party LSR（ Ask for what you don't have LSA  Details ）

2、 Mutual development LSU（ Requested by the other party LSA  Details ）

3、 Mutual development LS ACK （ Acknowledge receipt of LSU）

4、 Both parties set the status to Full（ Steady state ）.

OSPF  Supported network types

stay NBMA  in ,OSPF  Building a neighbor relationship requires that the network segments at both ends be consistent 、 Consistent mask

stay P2P  in , No network segment is required 、 Consistent mask

stay P2MP  in , The default requirement is network segment 、 Consistent mask , But it can be modified

OSPF  Multicast address