Basic configuration of NP and OSPF

OSPF It is a very extensive dynamic routing protocol based on link state , It has a region （Area） Hierarchical structure , Good scalability , Fast convergence , Suitable for deployment on networks of all sizes .
stay OSPF in , Every router must have one Route-ID To identify yourself . In order to make OSPF The network is more stable and reliable , Routers are usually enabled Loopback Interface , And configure specific IP Address , And use this address as your own Route-ID.
OSPF The agreement defines 4 There are two different types of networks , They are broadcast networks （ Also known as Broadcast The Internet ）,NBMA（Non-Broadcast Multi-Access） The Internet 、 Point to point networks （ Also known as Point-to-Point or P2P The Internet ）, And point to multipoint networks （ Also known as Point-to-Multipoint The Internet , or P2MP The Internet ）. On the radio network and NBMA In the network , An election is needed DR（Designated Router） and BDR（Backup Designated Router）.DR and BDR It is through the router interface DR It depends on the priority , The router with the highest priority will be selected as DR, The second was elected BDR; If DR The interface priority of is the same , Has the highest Router-ID The router that will be elected DR, Then he was elected BDR.

// master OSPF Basic configuration
// Observation and understanding DR\BDR The election process of
//OSPF Modification method of interface overhead
//OSPF The role of passive interfaces
//OSPF Configuration of authentication function

Here's the picture , The whole network is running OSPF.R1、R2、R3 The link between is located in the area 0 in ,R2 And R3 The link between is also located in the area as a backup link 0 in ,R2 And R4 The link between is located in the area 1 in ,R3 And R5 The link is located in the area 2 in .R4、R5、R1 Of Loopback 1 The interface simulates the networks in different branches and enterprise headquarters . Through the right OSPF After the configuration , Normal communication shall be realized between the networks of different branches and between the networks of branches and enterprise headquarters .

// To configure OSPF Routing protocol . Each router uses Loopback 0 Interface IP Address as your own Router-ID.

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// see R1 R2 R3 On OSPF The establishment of neighbors .



// Neighbor status is Full, It indicates that the neighborhood relationship has been successfully established .
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// see R1 Of IP Routing table .

// The headquarters router has obtained the route of the network segment where the interfaces of other routers are located .
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// see R4 Of IP Routing table .

//R4 Has also obtained the headquarters , Regional headquarters and branches 2 Routing of all network segments , Now we can communicate with each other .
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// see DR\BDR Election situation . stay DR\BDR In the election process , First, compare the routing interfaces DR priority , The router with the highest priority will be selected as DR, Next is BDR, The rest DRother.DR The default priority is 1,0 The representative will not participate in the election . If the interface DR Same priority , Compare the routing Router-ID, The maximum value is DR, The second is BDR, The rest of the for DRother.
// see R1、R2 DR\BDR Election situation .


//Loopback The network segment of the interface is point-to-point network by default , It can be observed that there is no election on the point-to-point network DR\BDR Of .10.0.12.0/24 For Ethernet segment , The default is broadcast network , So we need an election DR\BDR. Due to the default configuration , therefore R1 Of G0/0/1 R2 Of G0/0/0 Interface DR The priority values are 1, Therefore, it is necessary to compare Router-ID. therefore , Final R2 because Router-ID Larger and elected 10.0.12.0/24 On the network segment DR,R1 Then for BDR. in addition , You can also see that , stay 10.0.24.0/24 Network segment ,R2 Be selected as BDR,R4 Then for DR.
// Now modify R1 Of G0/0/1 Of DR The priority for 2, Hope to make R1 Become 10.0.12.0/24 The network segment DR,R2 by BDR. see DR\BDR Election situation .

// Observed or BDR, because DR\BDR The election is not preemptive . The interface needs to be closed and then opened , Or restart OSPF process , send DR\BDR A new election .
（reset ospf 1 process restart OSPF process ）

//R1 Has become 10.0.12.0/24 On the network segment DR.
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// see R2 The routing table for .

// Observation found that R2 visit R3、R5 Of Loopback The next hop of the route of the network segment where the interface is located is R1 Of 10.0.12.1, instead of R3
//tracert You can see the message from R2 To R5 The path .（ The message will go through R1 Of 10.0.12.1,R3 Of 10.0.13.3, Then arrive at R5）

//R2 View the interface on OSPF Cost value .

// You can see R2 Of S4/0/0 Interface （10.0.23.2） Of Cost The value is 48,G0/0/0 Interface （10.0.12.2） Of Cost The value is 1. Now modify R2 Of G0/0/0 Interface Cost The value is 2000, take R3 Of G0/0/0 Interface Cost The value is also changed to 2000.


// see R2 The interface of Cost value .（ You can see R2 Of G0/0/0 Interface Cost The value has been modified to 2000）

// The message goes directly through R3 arrive R5; Verified Cost The smaller it is , The principle of better routing .

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// To configure OSPF Passive interface , If one OSPF An interface of the router is configured as a passive interface （Passive Interface）, Then the interface will not send and receive OSPF The message will, for example R2 Of GE0/0/1 The interface is configured as a passive interface .（R2 And R4 Not established OSPF Neighborhood ）

// see R2、R4 Of IP Routing table .


// The observed R2 There are no branches on 1 Network routing , branch 1 Router R4 There are no other network routes on the .
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// To configure OSPF Authentication function .OSPF The configuration of the authentication function can be region based , It can also be interface based . Next , stay R1 The configuration is region based 0 The authentication function of , Use simple plaintext . see R1 Of OSPF Neighborhood information .

// You can see R1 There is no OSPF neighbor , This is because R2、R3 There is no matching authentication function configured on the .R2、R3 Failed to pass R1 Certification of , So I won't establish a neighbor relationship . stay R2、R3 Configure the corresponding authentication function on the .


// see R1 Upper OSPF Neighborhood information .（ The neighborhood relationship has been established normally ）

// Next , stay R2 The configuration is based on G0/0/1 Interface authentication , And USES the MD5 Ciphertext method .**（ see R2 Neighbors of OSPF Information ）** With no R4 Build a neighborhood

// stay R4 Of G0/0/0 Configure function authentication on the interface .

// Re in R2 Check out OSPF Neighborhood information .

/ Still no neighbor information , This is because I was in R2 G0/0/1 The passive interface is configured on the interface , The interface will not receive and send messages . Now delete OSPF 1 View neighbor information through the passive interface in .

R4 I already have it in my neighbor information R2.