Hcip OSPF knowledge summary

OSPF    open Shortest path first protocol      No category Link state routing protocol

        The public agreement ; Cross layer encapsulation to IP Headlines , Agreement No 89; Multicast update ：224.0.0.5  224.0.0.6

        Trigger update 、 Cycle update （30min）

        Need structured deployment ： Zoning   Address planning

Packet type

Hello： For neighbors 、 Adjacency     Find out 、 establish 、 Keep alive    hello time Default 10s or 30s

DBD： Database description package

LSR： Link status request

LSU： Link status update  

LSack： Link status confirmation

State machine  

Down： Once sent locally hello The package goes to the next state

Init： initialization   received hello If the package exists locally RID Go to the next state

2way： Two way communication    A sign of neighborhood building  

Matching conditions ： The point-to-point network will directly enter the next state ; MA The network type will be DR/BDR The election , Not DR/BDR You will not be able to enter the next state ;

Exstart： Pre start    Use similar hello Of DBD Conduct the election of master-slave relationship ,RID Big priority is preferred to enter the next state

Exchange： Quasi exchange    Use the real DBD Share the database directory , Need to use ACK confirm

Loading： load       Use LSR/LSU/LSAck To get the unknown LSA Information ;

Full： forward     A sign of the establishment of adjacency

oSPF The basic configuration of

[r1]ospf 1 router-id 1.1.1.1  Startup time , The process number needs to be defined ; Into the The program number is only locally unique

[r1-ospf-1]

Declare ：ospf When the agreement is announced, it needs to be divided into regions

  Regional division rules

1、 Star topology , Area 0 For the central backbone area , Others are greater than 0 It is a non backbone site area

2、 Must have ABR-- Area border router

 [r2-ospf-1]area  0     

Enter the area first , Then declare the interface belonging to the region in the region , The announcement must Carry anti mask

[r2-ospf-1-area-0.0.0.0]network 12.1.1.2 0.0.0.0

[r2-ospf-1-area-0.0.0.0]network 2.2.2.2 0.0.0.0

[r2-ospf-1-area-0.0.0.0]q

[r2-ospf-1]area  1

[r2-ospf-1-area-0.0.0.1]network 23.1.1.1 0.0.0.0

After the startup configuration is completed , Sending and receiving between neighbors hello package , Build a neighborhood ; Generate Neighborhood watch ：

[r2]display  ospf peer

[r2]display  ospf peer  brief

After the neighbor relationship is established , Conditional matching between neighbors , Successful matching can be established as adjacency ; Adjacency relationships will use DBD Package for master-slave relationship election , Then the master gives priority to DBD Share database directory information , Thus ultimately based on LSR/LSU/LSAck To get the unknown LSA Information ; When the whole network is collected LSA After the message , Loaded locally LSDB（ Link state database ）-- database surface

<r2>display  ospf lsdb  

<r1>reset ospf process

Warning: The OSPF process will be reset. Continue? [Y/N]:y 

1、DBD Carry... In your bag MTU value , Ask neighbors MTU Values must be the same , Otherwise it will get stuck in exstart or exchange state ; Huawei is not enabled by default MTU testing

[r1]interface GigabitEthernet 0/0/1

[r1-GigabitEthernet0/0/1]ospf mtu-enable

2、 Implicit confirmation — Do not use confirmation package , Instead, the serial number of the master device is copied from the device to confirm the receipt of the master DBD

OSPF Marker bit    I   M    MS       

I by 1 The first one sent locally DBD package

M by 0, Represents the last... Issued locally DBD    

MS by 1 On behalf of the Lord , by 0 For from

After the database is established , Local based on SPF Route selection rules , Calculate the shortest path to the unknown network segment and load it on Routing table in  

O IA Inter domain routing      O E1/2  Extraterritorial routing      ON1/2  NSSA Extraterritorial routing

<r1>display  ospf routing  Huawei view

SPF The condition that a protocol neighbor becomes an adjacency relationship

In a point-to-point network , be-all OSPF Neighbors will be directly established as adjacency ;

stay MA In the network , To avoid a lot of repetition LSA to update — because OSPF It needs to be carried out between adjacent rooms DBD contrast , Therefore, there is no interface water partition mechanism ; So it must be carried out DR/BDR The election , Not DR/BDR Only establish a neighbor relationship between ;--- In every one of them MA There needs to be an election in the network ;

Election rules ：

1. priority     The value is excellent , The default is 1;       if 0 To abandon the election ;
2. Same priority , Compare the performance of all the equipment of the candidate interface router-id, The value is excellent ;

[r1-GigabitEthernet0/0/1]ospf dr-priority 2

Modify the priority of the selected interface

Bear in mind ：DR Election non preemption , Therefore, after modifying the priority , must Restart the candidate equipment ospf Process to re-election

 OSPF Irregular areas of

a ABR If the equipment is not connected to the backbone area 0, By default, inter region routing cannot be shared

        Away from the non backbone area of the backbone ; Discontinuous backbone

Solution ：

Between legal and illegal ABR On the establishment of tunnel, Then announce it to ospf Agreement

shortcoming ： Cycle update 、 Keep alive , Trigger the update to occupy resources in the intermediate crossing area ;

          Poor route selection  --  When ospf Learn two common goals , But when different areas come at the same time , The backbone area is preferred ;

Tunnel Areas should be declared in the same area

Virtual link --- Between legal and illegal ABR Establish virtual link on , By legal ABR Illegal ABR To authorize ;

                Make illegal ABR You can share routes between regions ;

                Because there is no new path , Therefore, there is no problem of poor route selection ;

[r2-ospf-1]area  1     Two sets of ABR Common area

[r2-ospf-1-area-0.0.0.1]vlink-peer 4.4.4.4  Opposite end ABR Of RID

  Multi process bidirectional republication

On the same device , Different processes can work on different interfaces , Build their own neighborhood , Generate their own databases （ Do not share ）; Only the routes calculated by them are loaded into the same routing table ; An interface can only be declared by one process ; Two way republication ,ASBR（ Autonomous system border router 、 Protocol boundary router ）, Two way sharing of routes generated by different processes or protocols ;

[r2]ospf 1

[r2-ospf-1]import-route ospf  2

[r2-ospf-1]q

[r2]ospf 2

[r2-ospf-2]import-route ospf  1

OSPF Various LSA --- Database table

Class alias                The scope of communication                  Notifier                       The information carried

1 class LSA-router         Within the region           Each router in this area        The direct connection topology of each device in this area

2 class LSA-Network      Within the region               Of this network segment DR                   Topology of the network segment

3 class LSA-summary      Whole OSPF Domain            ABR                        O IA Inter domain routing

4 class LSA-asbr         except ASBR Outside the area     ABR                        ASBR The location of

                    Whole ospf Domain ;ASBR Use... In your area

                    1 Class tag location

5 class LSA-ase           Whole OSPF Domain            ASBR                       O E  Extraterritorial routing

7 class LSA-nssa          A single NSSA In the area      ASBR                       O N  Extraterritorial routing