OSPF protocol summary

OSPF： Open shortest path first protocol

OSPF Data packets of ：hello package  DBD package  LSR package LSU package LACK package

OSPF State machine

Down State start-up OSPF after , send out hello package

Init State After receiving the opposite end hello package , And the package contains RID, Now enter the next state

Two-Way State Mark the establishment of neighbor relationship , At this time, condition matching

Exstart State Use a that does not carry data DBD Package for master-slave relationship election

Exchange State Use... That carries data DBD Package to share database directory information

Loading State Load the opposite DBD Directory information in the package , And then with the local LSDB Compare database directory information , Then decide to send LSA/LSR/LSU package

FULL State  It marks the confirmation of adjacency relationship

OSPF working process ：
Start in configuration OSPF After completion , Local OSPF It will report to all local running OSPF Protocol router multicast address sending hello package . This hello The packet will carry the local route OSPF Of RID And local known neighbors RID. Then record the collected neighborhood relations to the local OSPF On the neighbor list of { Neighborhood watch }

After the neighbor table is established , Condition matching , Success starts to build adjacency .

After the adjacency relationship is established ,OSPF Both parties who establish the receiving relationship will use the one without data DBD Package for master-slave relationship election . After the election is completed and the master-slave relationship is decided , The leading Party will first use carry LSA Link directory data DBD Share database directory with package . And by sending LSR/LSU/LACK Package request / obtain / Confirm unknown local unknown link LSA Information , Finally, complete the establishment of local database LSDB

Local OSPF The routing protocol is based on the local link state database , To generate a directed graph of the routing topology . Re pass SPF The algorithm transforms a directed graph into a spanning tree , And calculate the best route for the local route to the unknown network segment , Finally, the best routing information is generated and added to OSPF In the routing table

complete OSPF After convergence , There are still cycles between routes （10s/30s） Send each other hello Package to keep alive and every 30 A periodic update is performed once a minute

 ospf Basic configuration   

[R1]ospf 1 router-id x.x.x.x

[R1] area x

[R1-ospf-1-area-x.x.x.x] network x.x.x.x  x.x.x

About OSPF Irregular region problem

Away from the backbone of the non backbone

Discontinuous backbone

Solution ：

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

shortcoming ： Periodic hello And update , Including triggering updates , Poor route selection

 2. OSPF Virtual link of   

[r2]ospf 1

[r2-ospf-1]area 1 

[r2-ospf-1-area-0.0.0.1]vlink-peer 4.4.4.4 

[r2]display  ospf vlink

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

3. Multi process bidirectional republication

In the network , Running multiple routing protocols or different processes of the same protocol, because the protocols cannot communicate and calculate directly , Re publishing is needed to realize route sharing

Re release single point, double point and multi point       One way, two-way

[r4]ospf 1

[r4-ospf-1]import-route  ospf  2

[r4-ospf-1]q

[r4]ospf 2

[r4-ospf-2]import-route  ospf  1

ospf Certification of Ensure the safety of data communication between neighbors

Interface authentication

[r6-GigabitEthernet0/0/1]ospf authentication-mode md5 1 cipher 123456

Regional certification

[r1]ospf 1

[r1-ospf-1]area  1

[r1-ospf-1-area-0.0.0.1]authentication-mode md5 1 cipher 123456

Virtual link authentication

[r10-ospf-1-area-0.0.0.4]vlink-peer  9.9.9.9 md5 1 cipher 123456

Silent interface   Resource consumption is large and needs to be closed

[r2]ospf 1

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

OSPF Of DBD package --- Implicit confirmation of sorting problem

The purpose is to avoid sending and carrying at both ends at the same time LSA Of DBD Headlines , Cause link congestion ;   Therefore, in order to keep the order normal ,DBD Implicit confirmation is required ;

Topology is better than routing   1/2LSA The calculated route is better than 3/4/5/7 Class calculated

Internal is better than external   3 Class is better than 4/5/7 class

type 1 Better than type 2  E1 be better than E2,N1 be better than N2,E1 be better than N2,N1 be better than E2;

E1 And N1 meet , or E2 And N2 meet , Compare the total measurement first （ start + Along the way ） Xiaoyou ; The measurement is consistent 5 Class is better than 7 class

Summary

Interregional ABR There are three types that will be passed LSA To summarize

stay ASBR On , Import by republishing 5 class /7 class LSA Get into OSPF Summarize when in the field

Special area

The terminal area ： It just keeps 1.2.3 Class LSA stay LSBD On the table

Completely peripheral area ：LSDB The database table has only one default route and 1 Classes and 2 class LSA Information

Incomplete ending area （NSSA）： Only... Will be saved in the complete terminal area 1 class ,2 class ,3 Class LSA, And this area will no longer accept 4 Classes and 5 class LSA, stay NSSA Intra domain ,5 class LSA Converted to 7 class LSA, Connecting the backbone area ABR It's equivalent to becoming ASBR, conversion 7 Class is 5 class ( Omit 4 class LSA) Send to backbone area

Completely NSSA Area , stay NSSA Further refuse to learn based on the region 3 class LSA

SPF Algorithm ： Shortest route first algorithm , The local route selects the optimal solution to reach other routes in the region .

Local routes first choose other routes that can reach directly （ Within the region ）

At this time, in the arrived route , Select the next hop route with the lowest cost , And list its direct （ Except for the starting route ）

At this time, if there is a route to reach the known existence （ Use the new line to reach the same route ）, Then compare the accumulated cost value , Choose the one with low cost

Repeat the previous ②,③ step , Until all the cost values are listed , At this point, you can draw a tree view ）