OSPF Open shortest path first protocol

Lu Jia Xuan , Fast convergence , Slightly less resources （ be relative to RIP Come on ）

OSPF edition

ospfv1( Days off in the Laboratory ),ospfv2 --- IPV4 ospfv3 ---lPV6

RIPV2 and OSPFV2 The similarities of

1,RIPV2 (224.0.0.9） and ospfv2 (224.0.0.5,224.0.0.6） They all send information in the form of multicast .224.0.0.X The multicast address of --- Local link multicast ---- TTL Set to 1

2,RIPV2 and OSPFV2 Are called classless routing protocols .

3,OSPFV2 and RIPV2 All support manual authentication

4, OSPFV2 and RIPV2 All support equal overhead load balancing

RIP and OSPF Difference point ：RIP It can only be used in small networks ,OSPF It can be applied to medium and large networks .OSPF Support structured deployment （ Zoning ）

The purpose of regional division ： Transfer topology information within the region , Transfer routing information between regions .

Zoning

Area border router ABR

Belong to multiple areas at the same time , An interface corresponds to a region and has an interface in the region 0 in

OSPF If the network has only one area , Such a network is called a single area oSPF The Internet ; If there are multiple areas , It is called multi region OSPF The Internet .

Requirements for area division

1, There must be... Between areas ABR equipment （ There can be multiple ABR equipment , One ABR There can also be multiple areas ）

2, Region division must be based on star topology

The middle region of star topology is called backbone region （ Area 0）

Area ID--- Distinguish and calibrate ospf Different areas in the network , from 32 Bit binary structure . The way of expression ： Dotted decimal means ; Use decimal system directly to express

OSPF working process

OSPF Data packets of

hello package cycle Find out , Building and keeping neighborhoods alive

hello Time ：10s（30s）

dead Time ：4 Times hello Time

RID The only global ; use the same pattern （ according to IP Format design of address , from 32 Bit binary structure ）

1. Manual configuration Just meet the above two conditions

2. Automatic generation

1. First, check whether the device is equipped with a loopback interface , If it exists, select the loopback interface IP Address as R ID; If there are multiple loopback interfaces , Then the one with the largest value will be selected as RID.

2. If there is no loopback interface , Then the... Of the physical interface of the device will be taken IP Address as RID, If there are multiple physical interfaces , Then the one with the largest value will be selected as RID.

DBD package Database description package

The database for LSDB（ Link state database ) LSA--- Link status notification

LSR package Link status request message

according to DBD Package comparison , Based on local unknown LSA Message sending request .

LSU package Link state update message

Really carry LSA Packets of information

LSACK package Link status acknowledgement message

OSPF There is 30min— Periodic updates .

OSPF State machine

TWo-WAY --- It marks the establishment of neighbor relations

（ Matching conditions ） The match is successful , Then you can enter the next state , If you fail , Will stay in the neighborhood , Use only Hello The package is kept alive periodically .

Principal subordinate relationship election --- By comparison RID To carry out ,RID Big for the main , The master can enter the next state first .

Explicit confirmation ： adopt ACK Bag to confirm Implicit confirmation ： Not through ACK Bag to confirm , Confirm by serial number

Use here DBD Package to complete the master-slave relationship election is mainly to distinguish from the previous neighbor state .

FULL state --- It marks the establishment of adjacency . The purpose is to distinguish from the neighbor state . Neighbor status can only be used hello The package is kept alive periodically , And the adjacent state can send and receive LSA Information .

down state --- start-up ospf after , issue hello After the package, go to the next state init( initialization ) state --- received Hello Package contains local RID, Then enter the next state

Two-way( Two-way communication ） state --- It marks the establishment of neighbor relations ( Matching conditions ） Matching failure , Will stay in the neighborhood , Use only Hello The package is kept alive periodically ; If the match is successful, it will enter the next state exstart( Pre start ） state -- Use a that does not carry data DBD Package for master-slave relationship election ,RID Big for the main , The master can enter the next state first exchange （ Quasi exchange ） state --- Use... With directory information DBD Package for directory sharing loading ( load ） state --- Based on DBD package , Use LSR/LSU/LSACK Three kinds of packet acquisition are unknown LSA Information . FULL state --- It marks the establishment of adjacency .|

OSPF Working process of

After the startup configuration is completed ,ospf Multicast will be provided to all interfaces running the protocol locally 224.0.0.5 In the form of hello package ; hello The bag will carry your own local RID And local known neighbors RID; after , Record the collected neighborhood relationships in a local table --- Neighborhood watch . After the neighbor relationship is established , Match the sacrificial parts . Failure , Stay in the neighborhood , Use only hello The package is kept alive periodically ; If the matching is successful, the adjacency relationship will be established . First , Use a that does not carry data DBD Package for master-slave relationship election , after , Use... With information DBD Package shared database directory information . after , Local use LSR/LSU/LSACK Three kinds of packets get unknown LSA Information . after , Complete the establishment of local database , Generate database tables ---LSDB. Last , Based on LSA Information , Generate directed graph and shortest path tree , after , Calculate the local routing information to the unknown network segment . Add this routing information to --- Routing table .

After convergence ,ospf Still every 10s (30s） send out hello The package is kept alive periodically ; every other 30MIN Make a periodic update .

Structural mutation

1, Add a new network segment --- Trigger update , Change the information immediately through LSU The package passes out , need ACK confirm . 2, Disconnect a network segment --- Trigger update , Change the information immediately through LSU The package passes out , need ACK confirm . 3, Unable to communicate ——dead time

OSPF The basic configuration of

1, start-up ospf process [r1]ospf 1 router-id 1.1.1.1

2, Create area [r1-ospf-1]area 0 [r1-ospf-1-area-0.0.0.0]

3, Declare

[r1-ospf-1-area-0.0.0.0]network 12.0.0.1 0.0.0.0（ Unmask , Continuous 0 And continuous 1 form ,0 The corresponding bit is immutable ,1 Corresponding to variable . You can make accurate announcements , You can also declare the scope ）

Purpose 1, Activate interface ;2, Publish route

[r1]display ospf peer --- see ospf My neighbor table

[r1]display ospf peer brief --- View neighbor profile

[r1]display ospf lsdb --- View database tables

[r1]display ospf lsdb router 2.2.2.2 --- Expand a LSA Information

Huawei equipment definition ospf The default priority of the protocol is --10

COST = Reference bandwidth / Real bandwidth --- The default reference bandwidth of Huawei equipment is 100Mbps

If the cost value is less than 1 Decimals of , Then directly follow 1 To calculate ; If it is greater than 1 Decimals of , Then take the integer part directly .

[r1-ospf-1]bandwidth-reference 1000 Change reference bandwidth , Modification requires that all OSPF The equipment of is changed to the same