Your company wants to install a hierarchical network that it can scale up over the next few years.
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The company is using a class B network address of 172.16.0.0.
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You have decided to divide the network into five areas: a backbone and four others.
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The subnet address ranges are:

• Backbone (Area 0): from 
  172.16.64.0 to 172.16.127.0
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• London (Area 1): from 
  172.16.0.0 to 172.16.31.0
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• Dublin (Area 2): from 
  172.16.192.0 to 172.16.255.0
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• Sydney (Area 3): from 
  172.16.32.0 to 172.16.63.0
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• SanFran (Area 4): from 
  172.16.128.0 to 172.16.191.0
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The IP addresses on each interface have a subnet mask of 255.255.255.0.
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You have decided to implement OSPF on your network.
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To do this you must

• enable the OSPF process on 
  each router
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• configure the OSPF areas
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• configure the interfaces on 
  each router that will run OSPF
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• configure route summarization 
  between the OSPF areas
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In order to configure the routers you must be in privileged mode.
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You enter configuration mode by typing @Rconfig@r at the prompt and pressing @UReturn@u twice to configure from terminal.
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Starting with the SanFran router you enter the command @Rrouter ospf 59@r.
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The number 59 is the process ID for the OSPF routing process.
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This enables OSPF routing on the SanFran router.
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Next you must configure the interfaces on this router for OSPF.
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You enter the command @Rnetwork 172.16.65.0 0.0.0.255 area 0@r.
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This defines any interface whose network address is 172.16.65.0 as an OSPF interface.
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It defines the area ID for this network.
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There are two other networks used on the SanFran router.
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These are configured for OSPF in the same way.
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The SanFran router is the ABR between area 4 and area 0 (the backbone).
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Next you may specify the address range for area 4 to summarize routes.
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To do this you enter the command @Rarea 4 range 172.16.128.0 255.255.192.0@r. You also specify an area range for the backbone with command @Rarea 0 range 172.16.64.0 255.255.192.0@r.
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OSPF uses VLSMs to conserve address space.

You could achieve this by changing the subnet mask for the IP addresses on the serial links from 255.255.255.0 to 255.255.255.248.

Serial lines need only two addresses - one for each end.
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By specifying the address range you also configure route summarization between area 4 and area 0.
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The SanFran router is now configured for OSPF.
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Before exiting configuration mode you should specify the range of addresses for the backbone.
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You exit configuration mode by pressing @UCTRL+Z@u.
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You can save the configuration in NVRAM by entering @Rcopy runn start@r.
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OSPF is now in RAM (running-config) and NVRAM (startup-config).
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Next, you configure the London router.
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You log on remotely to the London router using telnet by entering @Rtelnet london@r and then entering the London router's logon password, @Rcbtcbt@r.
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As before you need to be in privileged mode on the London router before you can configure it.
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You enter Privileged mode by typing @Renable@r at London's command prompt and entering its password, @Rcisco@r.
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Then you enter configuration mode by typing @Rconfig@r and pressing @UReturn@u twice to configure from terminal.
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You enable OSPF routing on the London router by entering @Rrouter ospf 59@r.
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You configure the three OSPF networks on the router by entering

@Rnetwork 172.16.68.0 0.0.0.255 area 0@r

@Rnetwork 172.16.66.0 0.0.0.255 area 0@r

@Rnetwork 172.16.1.0 0.0.0.255 area 1@r
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Then you specify the address range (and so configure route summarization) by entering @Rarea 1 range 172.16.0.0 255.255.244.0@r. You also specify an area range for the backbone with command @Rarea 0 range 172.16.64.0 255.255.192.0@r.
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The London router is now configured for OSPF routing.
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Before exiting configuration mode you should specify the range of addresses for the backbone.
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You exit the configuration mode by pressing @UCTRL+Z@u.
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You save the configuration in NVRAM by entering @Rcopy runn start@r.
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You then log out of the London router and exit back to the SanFran router by typing @Rexit@r.
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The Dublin and Sydney routers are configured in the same way.
@@
<F>Assume that you are in the process of configuring your company's internetwork.
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You are configuring it to run OSPF with a backbone area and four other areas.
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You have already configured the SanFran and London routers.
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You log on to the Dublin router by entering @Rdublin@r at the prompt.
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You can also do this by entering @Rtelnet dublin@r or @Rtelnet 172.16.66.2@r or @Rtelnet 172.16.67.2@r.
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You then enter the password, in this case @Rcbtcbt@r.
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You enter Privileged mode by typing @Renable@r and entering the password @Rcisco@r.
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You enter configuration mode by typing @Rconfig@r and pressing @UReturn@u twice to configure from terminal.
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You enter @Rrouter ospf 59@r to enable OSPF routing on the router (using a process ID of 59).
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You need to configure three interfaces on the Dublin router.
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You enter @Rnetwork 172.16.66.0 0.0.0.255 area 0@r to configure the first network.
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You then enter @Rnetwork 172.16.67.0 0.0.0.255 area 0@r to configure the second network.
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Finally you enter @Rnetwork 172.16.192.0 0.0.0.255 area 2@r to configure the third network.
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You specify the address range for area 2 using the command @Rarea 2 range 172.16.1.0 255.255.244.0@r. You also specify an area range for the backbone with command @Rarea 0 range 172.16.64.0 255.255.192.0@r.
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This command configures route summarization between area 0 and area 2.
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You press @UCTRL+Z@u to exit Configuration mode.
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You then save the configuration in NVRAM using the command @Rcopy runn start@r.
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And you log out of the Dublin router and exit back to the SanFran router by typing @Rexit@r.
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You next log into the Sydney router by entering @Rtelnet 172.16.65.1@r at the SanFran's prompt.
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You enter the password, @Rcbtcbt@r.
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You must be in Privileged mode on the Sydney router and so you enter @Renable@r and the password @Rcisco@r.
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Then you enter Configuration mode by typing @Rconfig@r.
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You enable OSPF routing on the Sydney router by entering @Rrouter ospf 59@r.
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The Sydney router has three networks to configure for OSPF.
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These are configured using the following commands:
 
@Rnetwork 172.16.68.0 0.0.0.255 area 0@r
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@Rnetwork 172.16.65.0 0.0.0.255 area 0@r
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@Rnetwork 172.16.32.0 0.0.0.255 area 3@r
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You then specify the address range for area 3 using the command @Rarea 3 range 172.16.32.0 255.255.240.0@r. was .1. now is .32. You also specify an area range for the backbone with command @Rarea 0 range 172.16.64.0 255.255.192.0@r.
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And you exit configuration mode by pressing @UCTRL+Z@u.
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You save the configuration to NVRAM by entering the command @Rcopy runn start@r.
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You then log out of the Sydney router and exit back to the SanFran router by typing @Rexit@r.
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Once you have OSPF running on your network, there are several commands that you can use to monitor the network.
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For example, you can use the Show ip ospf command to display general information about the OSPF routing process.
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From the output of this command you can see that the SanFran router is in two areas, the backbone and area 1.
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It has one interface in area 1 and two in the backbone area.
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You can also see that each area has a link-state update interval of 30 minutes.
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Area 1 will be updated in 18 minutes and 1 second while the backbone area will be updated in 17 minutes and 32 seconds.
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The Show IP OSPF command can also tell you how many times the SPF algorithm has executed in each area.
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In this case it has executed in area 1 three times and in the backbone area 6 times.
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You can display the current state of the routing table using the Show IP Route command.
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You can see from the output that the routing table of the SanFran router does not contain a default route.
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The routing table also indicates that three addresses are directly connected - these are the three interfaces that you have configured for this router.
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The routing table has identified a replace route from the with subnet between SanFran router to a network on the London and Dublin routers (172.16.67.0) via an interface on Dublin router (172.16.66.2).
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You can use the Show IP Protocol command to display the parameters and current state of the active routing protocol process.
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You can see from the output that the SanFran router is using the OSPF routing protocol.
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OSPF is routing for three networks, each on only one of the interfaces you have configured on the router.
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You can also see where the routing protocol is getting its information from to build the routing table.
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Finally you can trap OSPF events by turning on OSPF debugging using the command debug IP OSPF Events.
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In this case we can see that the SanFran router sent an update out on it's serial 1 interface.
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This update was acknowledged by the Dublin router (172.16.192.1).
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You turn off OSPF debugging using the command undebug IP OSPF Events.
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Your company's internetwork has been configured to run OSPF.
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You want to monitor the OSPF operation on the network.
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You enter the command @Rshow ip ospf@r to display general information about the OSPF routing process.
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You examine the contents of the routing table by entering the command @Rshow ip route@r.
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You enter @Rshow ip protocol@r to display the parameters and current state of the active routing process.
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You can turn debugging on by entering @Rdebug ip ospf events@r.
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As OSPF updates occur they are echoed to the screen.
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The debug events was given an event by bringing a serial interface down. It is also easily seen where the line was brought up again.
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You can examine OSPF on an interface with the shown ospf interface command.
