OSPF --- open shortest priority path protocol

Dynamic routing protocol ： Start a protocol between routers , Then the routers communicate with each other , Learn from each other and calculate to obtain the path of the previously unknown target network segment ;

RIP   OSPF  EIGRP   BGP   ISIS 

classification ：

be based on AS To classify  

AS- Autonomous systems    standard 16 Bit binary  0-65535  among 1-64511 public   64512-65535 private

              Expand 32 Bit binary

AS Run within —IGP agreement – Internal Gateway Routing Protocol  --  RIP/OSPF/ISIS/EIGRP

AS Running between —EGP agreement - External gateway routing protocol --   EGP/BGP

IGP Classification of protocols ：

【1】 Based on whether the subnet mask is carried during update ---   There are categories （ No ）     No category （ carry ）

【2】 Classification based on work characteristics    

1. Distance vector -DV   RIP/EIGRP   Directly share the routing table – Learn routing items directly    Small update volume
2. Link state -LS    OSPF/ISIS   Share topology information   -- Calculate routing entries locally   A lot of updates

OSPF： Open shortest path first protocol      Classless 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

One 、OSPF Protocol packets ：

1. Packet structure

1. 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

Two 、 state

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

LSA： Link status notification , Under different network conditions, different types of LSA Information to represent topology or routing entries ;

LSDB： Link state database   Load and store all kinds of LSA;

3、 ... and 、OSPF Working process of

OSPF After the agreement is started ,A Started to all local OSPF Direct interface multicast protocol 224.00.5 send out hello package ; Local hello The package carries the only one in the whole network router-id;

Router id effect ： Identify the router

Then the opposite end B function OSPF The agreed device will reply hello package , The hello If you carry A Of router id, that A/B Establish a relationship as a neighbor ; Generate Neighborhood watch

After the neighbor relationship is established , Conditional matching between neighbors , If the match fails, it will stay in the neighborhood , only hello Keep the package cycle alive ;

If the condition matching is successful, the adjacency relationship can be established ：

Adjacency sharing DBD package , Local and adjacent DBD Compare packages , Find a file that does not exist locally LSA Information directory ;

Then use LSR To ask , End to end use LSU Answer specific LSA Information , Then use it locally ack confirm , reliable ;

When the process is complete , Generate Database table ;

Then, based on the local database table , Enable SPF Route selection rules , Calculate the shortest path to all unknown network segments , Then add it to the local Routing table in ; Convergence complete ,hello Keep the package cycle alive , Every time 30min Send and receive again DBD To determine whether the database is consistent with the adjacent database ;

Structural mutation ：

1. New network segment Equipment directly connected to the new network segment , Will be used directly LSU Package to inform all local neighbors , Then, adjacency transmission and adjacency diffusion will spread to the whole network , need ACK confirm
2. Disconnect the network segment Equipment directly connected to the disconnected network segment , Will be used directly LSU Package to inform all local neighbors , Then, adjacency transmission and adjacency diffusion will spread to the whole network , need ACK confirm
3. Unable to communicate    dead time by hello time Of 4 times ; When dead time To the hour , Break the neighborhood , Delete the route entry generated by this adjacency ;

Four 、OSPF The basic configuration of

[r1]ospf 1 router-id 1.1.1.1  Startup time , The process number needs to be defined ; The process number is only locally unique ; It is recommended to configure the only in the whole network at the same time router-id; Generation order — manual Maximum in local loopback interface ip Address value    The maximum value in the local physical interface ip Address  

[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 declaration must carry an inverse 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

neighbor 、 The discovery of adjacency 、 establish 、 Survival depends on hello Package progress ;

Hello The parameters that must be completely consistent between neighbors in the packet ： Any parameter is different , All lead to the failure to establish neighbor relations （）

1. Subnet mask （ Huawei ） send out hello Source of package interface ip Address mask   
2. Hello dead time      -- OSPF The interface is related to the network type
3. Authentication field            -- Update security
4. Area ID              -- It is required that there be... Between areas ABR

5、 Terminal area markers          -- Special area

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

About OSPF,DBD Several knowledge points of the package ：

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

1. 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 ;

1. Letter

Cisco

O - OSPF, IA - OSPF inter area

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2

O In the same area , Calculated by local topology

O IA Inter domain routing ,ABR The route calculated through the topology of other regions , Then share to another area ; Local area, another area

O E1/2  Extraterritorial routing     After other agreements or other processes are produced , adopt ASBR Republish to OSPF agreement

ON1/2  NSSA Extraterritorial routing    After other agreements or other processes are produced , adopt ASBR Republish to OSPF agreement , At the same time, the device learning this route is in ospf A kind of NSSA In a special area of

<r1>display  ospf routing 

1. Measure （cost）

Cost value    Reference bandwidth / Interface bandwidth         Huawei equipment , The loopback interface is not calculated as a path ; The default reference bandwidth is 1000M;

optimization cost The minimum path of the sum of values ;

5、 ... and 、 OSPF 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 , The candidate equipment must be restarted ospf Process to re-election

OSPF The convergence of is called LSA flooding , Also known as LSDB Sync ;

• OSPF Interface network type –OSPF The protocol works under different network types of interfaces , Its different ways of working

Interface network type                  OSPF Interface network type （ospf Operation mode ）

LoopBack 0.          Cisco – LoopBack   No, hello package    With 32 Bit host routing

                     Huawei — Is shown as p2p type     For the actual LoopBack Operation mode

Point to point

（ String line HDLC/PPP/GRE）   p2p. hello time10s  Automatic neighbor building    No election DR/BDR

BMA

Ethernet                 Broadcast  hello time 10s  Automatic neighbor building     choose DR/BDR

NBMA

Frame relay                nbma  hello time 30s    Create neighbors manually    choose DR/BDR

MGRE                 p2p. hello time10s  Automatic neighbor building    No election DR/BDR – In a network segment, only

There can be a neighbor ; Huawei equipment is in a MGRE Network segment , The interface is point-to-point

When working in a way , Only and first received hello Establish a neighbor relationship with your device ;

Cisco In this case, there will be a tumbling of neighbors ;

notes ： stay MGRE Environment , The interface defaults to ospf The working mode is point-to-point , This cannot be achieved in this way NBMA All the neighbors of the network segment are connected ; Therefore, you can only modify the working mode of the interface ：

modify MGRE Network segment All interfaces by Broadcast Operation mode , Remember that if some interfaces are modified to Broadcast, The other part of the interface remains point-to-point , because hello time The same can establish neighbors , But the working mechanism is DR/BDR The electoral office is different , Therefore, the network segment cannot converge normally ;

1. meanwhile , We must pay attention to the network topology ; If the network segment is a fully connected mesh structure , that DR The election will proceed normally ; But in case of partial mesh or center to site topology , Will be possible DR Wrong location problem ;
2. If the network topology can only be partial mesh or center to site , Manual intervention is required DR Location

Or change the working mode of all interfaces to point to multipoint working mode ;

Ospf Point to multipoint working mode ： It can only be configured manually , It is applicable to some mesh topology ;

  Hello time30s, No election DR/BDR, Automatically build neighborhood relationships ;

6、 ... and 、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

1. Away from the non backbone area of the backbone
2. Discontinuous backbone

Solution ：

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

shortcoming ：1、 Cycle update 、 Keep alive , Trigger the update to occupy resources in the intermediate crossing area

1. 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

1. 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

   Cisco In order to avoid the occupation of the intermediate area by periodic information , Cancel all periodic behaviors on the virtual chain ;--- unreliable

   Huawei still keeps the cycle alive on the virtual chain 、 to update --- Resource occupation in the middle area

1. Multi process bidirectional republication （ recommend ）

Multi process --- 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

<r1>display  ospf lsdb

<r1>display ospf lsdb router 1.1.1.1

                    Class alias  link-id（ The number in the catalog ）

All categories of LSA, All carry the following information

  Type      : Router    Class alias   Here is 1 class

  Ls id     : 1.1.1.1     link-id  The number in the catalog

  Adv rtr   : 1.1.1.1      Notifier --- The LSA Of the update source device RID

  Ls age    : 1359     Aging time   1800s The cycle is refreshed to 0   Trigger update return 0  Maximum 3609s

  Len       : 48

  Options   :  E 

  seq#      : 8000000c    Serial number

  chksum    : 0x818c     Check code

OSPF Of LSA yes 1800 It will be updated once, and the serial number will be added once

LSA A comparison between the old and the new

1、 Will compare the serial numbers first , The larger the serial number, the better ,

2、 If the serial numbers are the same , Will compare the check values （checksum) The bigger the better

3、 If the check value is the same , Will compare LSA Age Time , Is it equal to MAX-age Time （3600）

4、 If age Time is not equal to max-age Time , Will compare their differences , If the difference is large 15 minute （900 second ）, The small ones are excellent

5、 If age Time is not equal to max-age Time , Will compare their differences , If the difference is less than 15 minute , The explanation is the same LSA, Ignore one of them

Under what circumstances LSA Will update ：

1、1800 The expiration date will be updated periodically

2、 Trigger update （ Interface address change （ increase , Or delete ）, Modify the interface cost value , Delete interface , Or delete the announcement ）

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

Class alias                 link-id                        Notifier

1 class LSA-router        Announcer's RID              Each router in this area

2 class LSA-Network      DR Interface ip Address           Every MA In a segment DR

3 class LSA-summary     Target network number of inter domain routing        ABR, After passing the next station ABR when , Change to new ABR

4 class LSA-asbr         ASBR Of RID                 ABR, After passing the next station ABR when , Change to new ABR

5 class LSA-ase          The target network number of the extraterritorial route        ASBR stay ospf Internal transfer does not change

7 class LSA-nssa         The target network number of the extraterritorial route               ASBR