OSPF summary

OSPF（open shortest pass first Open shortest path first ）
Attached is the mind map

Basic concepts

characteristic

- 1、OSPF It is a classless link state routing protocol , Cross layer packaging to three layers , Agreement No 89;
- 2、 Multicast address ：224.0.0.5（BDR Multicast address ）  and 224.0.0.6（DR The multicast address of ）;
- 3、 Work based on Topology , A lot of updates —— Need structured deployment —— Zoning 、 Address partition ;
- 4、 The convergence rate is very fast , But large network configurations are complex .
- 5、OSPF Measure ： Metrics for all outgoing interfaces from source to destination , It's inversely proportional to the interface bandwidth （10^8/ bandwidth ）

ospf Five data packets

• 1、hello package – Multicast sending and receiving , For neighbors 、 The discovery of adjacency 、 establish 、 Life cycle

• 2、DBD – Database description package -- Local LSDB（ Link state database ） Catalog

• 3、LSR— Link status request – It is used to query the local unknown of the opposite end LSA Information

• 4、LSU-- Link status update – For sharing every specific LSA Information

  • LSA– Link status notification – Specific one by one Routing or topology information , Not a packet , be-all LSA It's using LSU This kind of packet is forwarded ;

• 5、LSack Link status confirmation – Confirmation package

ospf7 Class state machine

• 1、Down： Once it's sent out locally hello The package goes to the next state ;

• 2、Init initialization ： Received locally hello There are local RID Go to the next state ;

• 3、Two-way Two-way communication ： A sign of neighborhood building ;

• Condition matching from neighbor to adjacency ： Point to point networks go straight to the next state ;MA The Internet is going to be DR/BDR The election of （40s）, Not DR/BDR Don't go to the next state ;

  • Between neighbors hello Some parameters in the package must be completely consistent , Otherwise, you can't establish a neighbor relationship ;
    Hello and dead time 、 Area ID、 Certification parameters 、 Terminal area markers ; In addition, in Huawei's equipment OSPF The interface between neighbors is required to be configured ip Address , The mask length must be consistent ;

  • MA In the network DR and BDR Comparison order of election information

    • First, compare the manually set RID– If none or equal -> Loopback interface IP– If none or equal -> Interface number

• 4、Exstart Pre start ： Use similar hello Of DBD Conduct a master-slave election ,RID Major , The Lord has priority to enter the next state ;

• 5、Exchange Quasi exchange ： Use real DBD Package for database directory sharing , need ack;

• 6、Loading load ： Use LSR/LSU/LSack Get unknown LSA Information ;

• 7、Full forward ： A sign of the establishment of adjacency .

ospf Routing table synchronization process

• After the adjacency relationship is established , Meet the conditions and enter the next state , adopt DBD/LSR/LSU/LSAck To synchronize information .
• After the database table synchronization is completed , The interaction between neighbors is completed , only hello Bao Huo Bao ; Then local based database tables ;
• Convert to directed graph , Then it is transformed into a tree structure , Finally, the shortest local path to all unknown network segments , Loaded in the local routing table

ospf Three tables

• Link state database table

  • List information about other routers in the network , This shows the network topology of the whole network

• Neighborhood watch

  • List all neighbor routers that have established adjacency relationship for each router

• Routing table

  • List through SPF The algorithm calculates the best path to each connected network

OSPF The interface network type of

• 1、 Point to point : DA 224. 0. 0. 5( Even if the setting nei ghbor Also multicast updates ), A pair of routers form an adjacency relationship . nothing DR, Each subinterface belongs to a different IP subnet .

• 2、 Point to point : DA: 224. 0.0. 5 ( Even if the setting neighbor Also multicast updates ), nothing DR, The same IP subnet .Ptp and ptmp Can't form neighbors ( stay PTMP in hello-interval 30 dead -interval 120)

  • MGRE You can build different topologies ：

    • 1、 Star type – Center to site – Radial The central site is DR, Cancel BDR
    • 2、 The whole company — No more attention is needed DR
    • 3、 Partially reticulated — Based on the normal sharing in the whole network segment LSA To consider the best DR Location

• 3、 Point to multipoint non broadcast : DA: unicast , nothing DR, same IP subnet .

• 4、 NBMA: DA: unicast , choose DR (DR and BDR Must be directly connected to all other routers ), Same as - -IP subnet . Fully or partially interconnected .

• 5、 radio broadcast : The election DR, All routers send messages to 224.0.0.6 (DR Listen to this address ), then DR Send a message to 224.0.0.5,DR Establish adjacency with all routers , Between all routers to 2way state ( Even if the setting neighbor Also multicast updates ). same IP subnet , Fully or partially interconnected .

• 6、 Feature summary :

  • You don't have to vote for a family DR and BDR
  • Multiple access requires elections DR and BDR
  • If you are not broadcasting, you have to specify your neighbors manually , All non broadcast updates are unicast
  • neighbor Designated after the order cost It works only if it's not broadcast

OSPF Irregular region problem

Non backbone and discontinuous backbone far away from the backbone

• 1、tunnel In the backbone area and illegal ABR Build a tunnel between , The tunnel link is then declared to OSPF Agreement

  • 1） Periodic hello And update , Including triggering updates , The middle crossing area will be occupied uniformly ;
  • 2） Poor route selection

• 2、OSPF Virtual link of

By illegal ABR equipment , Through the legal of the direct connection area ABR To authorize , To forward the route , Because there are no new links , Therefore, there is no problem of poor route selection

-  shortcoming ： Two on the virtual chain ABR The problem of periodic resource occupation between ;

	- 1） In Cisco , Cancel the cycle behavior of two devices ,hello、 Updates are sent and received once ;-- unreliable 
	- 2） In Huawei , Retention period -- Take up resources 

-  Multi process bidirectional republication 

	- ospf Multi process ： Multiple processes on a router , Each process has its own database , Calculate routing entries independently , And calculate all that are not shared ; Finally, all the best paths are loaded into the same routing table ;
	-  An interface of a router can only work in one process ;
	-  It can be used to solve irregular areas , Work irregular locations in different processes , Realize separation , Then we use the republishing technology to share the routing table ;   It solves the problems of poor route selection and resource occupation 

7 class LSA

• LSA Type1：router LSA Generated by each router for its region LSA, Describe the status and cost of the router link in this area . A border router may generate multiple LSA TYPE1.
• LSA Type2： from DR produce . It contains all link status and cost information connected to a regional router . Only DR This information can be monitored .
• LSA Type3： from ABR produce , contain ABR Connection information with local internal router , Can describe this area to area0 Link information . It usually summarizes the default routes instead of transmitting the summarized OSPF Information to other networks .
• LSA Type4： from ABR produce , Sent from the trunk area to other areas ABR, contain ASBR Link information , And LSA TYPE 3 The difference is that TYPE 4 Describe to OSPF External routing of the network , and TYPE 3 Then describe the route in the region .
• LSA Type5： from ASBR produce , Contains information about links outside the autonomous region . Except for stub area and full stub area ,LSA TYPE 5 Send throughout the network .
• LSA Type7： from ASBR About NSSA Information about .LSA TYPE 7 Can be converted to LSA TYPE 5.
  

OSPF Optimize – Reduce LSA Update quantity of

1、 Summary — Reduce the number of routing entries in the backbone area

• OSPF The protocol does not support interface summary , In an area , Topological information is transmitted between adjacency , Cannot summarize ; Therefore, it can only be summarized at the boundary equipment of interactive routing

  • 1） Inter domain routing summary – Between regions ABR On , Perform summary configuration when interacting with inter area routing entries
  • 2） Extraterritorial routing summary —ASBR The external routing entries are passed through the republication protocol , Share to OSPF In the agreement , You can summarize

2、 Special area -- Reduce the number of routing entries in non backbone areas

• non-existent ASBR situation

  • 1. The terminal area – Refuse 4/5 Class LSA; The backbone area is connected by this area ABR Post a message to this area 3 Class
  • 2） Completely peripheral area Based on the peripheral region , Further reject 3 Class LSA; Keep only one 3 Class
    First, configure all routers in the whole area as the end area ; Then only in the area connecting the backbone ABR Complete configuration on the

• There is ASBR situation

  • NSSA Incomplete ending area

      - 1) The area rejects 4/5 class LSA, The backbone area is connected by this area ABR Send a message to the area 7 Class ; When importing an extraterritorial route, the ASBR be based on 7 Class import , Connect the backbone through this area ABR When passing to the backbone area , Convert to 5 Class enters the backbone area ;
    

  • Completely NSSA

    • stay NSSA On the basis of , Further reject 3 class LSA, The backbone area is connected by this area ABR Post a message to this area 3 Class ,
    • First, configure the area as NSSA Area , After that, only the backbone is connected in this area ABR Complete configuration on the

ospf Extended configuration

1） authentication

• effect ： Between directly connected neighbors or neighbors , Configure an identity verification key to protect neighbors 、 Security of data communication between neighbors

• 1） Interface authentication

  • Configure... On the interface of direct connection
    Patterns at both ends 、 Number 、 The secret key must be completely once

    • ospf authentication-mode md5 1 cipher 123456

• 2） Regional certification

  • Connect the router R1, All belong to area 1 All interfaces shall be certified

    • authentication-mode md5 1 cipher 123456

• 3） Virtual link authentication

  • vlink-peer 9.9.9.9 md5 1 cipher 123456

2） Silent interface

• Definition and function

  • Router connection PC Interface of terminal equipment , These interfaces are accessible to the whole network , Will be declared in the routing protocol ; Therefore, these interfaces will also periodically send routing protocol information to the terminal below , Cause resource occupation , And safety issues ; Therefore, these interfaces need to turn off sending RIP/OSPF Wait for protocol packet behavior
  • Remember not to configure the backbone interface between the router and the router , It will cause neighbors to be unable to send and receive routing information , Unable to establish neighbor relationship

• Configuration information

  • [r2]ospf 1
  • [r2-ospf-1]silent-interface GigabitEthernet 0/0/2

3） Speed up convergence

• By modifying the relationship between neighbors hello and dead time, Can achieve faster convergence , But if the frequency is too high, it will occupy more hardware resources ; so hello time by 10s when , It's not recommended to speed up ; hello time by 30s It can be modified as appropriate ;
• Between neighbors hello time and dead time Must complete consistent , Otherwise, you can't establish a neighbor relationship ;
• Modify the local hello time, Local dead time Automatically 4 Matched by relationships ; The end-to-end time remains the same , The configuration of both ends needs to be completely consistent manually ;
• [r2-GigabitEthernet0/0/0]ospf timer hello 10

4、 Default route

• 1）3 Class default

  • Special areas are automatically generated ： Peripheral 、 Complete endings 、NSSA、 Completely NSSA
  • Peripheral 、 Complete endings 、 Completely NSSA this 3 Special areas in , After the configuration is completed , The backbone area is connected by this area ABR Send... To the inside of the area ;
  • In Huawei equipment ,NSSA And completely NSSA, After the configuration is completed , The backbone area is connected by this area ABR Release internally 7 Class ;
  • So completely NSSA Will have 3 Classes and 7 There are two default classes , Internal is better than external , So trust 3 class ;

• 2）5 Class default -- External routing , Republished

  • In the routing table of the local router , After there is a default route generated in any way , By special instructions , Republish it to OSPF Agreement ;

  • [r9-ospf-1]default-route-advertise

    • The default route obtained by other means in the local route table , Republish to internal OSPF Agreement Default import type 2 route

  • [r9-ospf-1]default-route-advertise always

    • Force republication of default routes – Even if there is no default route in the local route table , It also forces a default route to be published internally Default import type 2 route

  • [r9-ospf-2]default-route-advertise type 1

    • Change to type 1;

• 3）7 Class default

  • NSSA Or completely NSSA, Automatically connect the backbone from this area ABR issue , But in complete NSSA There will also be 3 Class default , So completely NSSA in 7 Class defaults to meaningless ; Default 5 Class is also a type 2;

  • [r6-ospf-1-area-0.0.0.3]nssa default-route-advertise

    • By hand 7 Class default , The premise is NSSA In the region

• Priority of route selection

  • Internal is better than external so 3 Class is better than 5/7
  • If both are 5 class Or both 7 class type 1 Better than type 2 The same type , Compare priorities , Same priority comparison cost value , Fully consistent load balancing ;
  • if 5、7 Class encounter , type 1 Better than type 2; The same type , Compare priorities , Same priority comparison cost value , Exactly the same 5 Class is better than 7 class ;