Examine the exhibit. You are asked to configure the routers R1, R2, R3, and R4. (Refer to the IP addressing table below.) Which configuration command series is required to ensure that router R1 will NOT be receiving Type 3, 4, or 5 LSAs?

Examine the exhibit.

300-410 Part 03 Q04 032

300-410 Part 03 Q04 032

You are asked to configure the routers R1, R2, R3, and R4. (Refer to the IP addressing table below.) Which configuration command series is required to ensure that router R1 will NOT be receiving Type 3, 4, or 5 LSAs?

R1 interface E0 - 172.31.200.1/21
R2 interface E0 - 172.31.200.2/21
R2 interface E1 - 172.31.208.2/21
R3 interface E0 - 172.31.208.3/21
  • R1(config)# router ospf 5
    
    R1(config-router)# area 5 stub
    
    R1(config-router)# network 172.31.200.0 0.0.7.255 area 5
  • R2(config)# router ospf 5
    
    R2(config-router)# area 5 stub no-summary
    
    R2(config-router)# network 172.31.200.0 0.0.7.255 area 5
    
    R1(config)# router ospf 5
    
    R1(config-router)area 5 stub
    
    R1(config-router)# network 172.31.200.0 0.0.7.255 area 5
  • R1(config)# router ospf 10
    
    R1(config-router)# area 5 stub
    
    R1(config-router)# network 172.31.200.0 255.255.248.0 area 5
  • R2(config)# router ospf 10
    
    R2(config-router)# area 5 stub no-summary
    
    R2(config-router)# network 172.31.200.0 255.255.248.0 area 5
Explanation:
At the area border router (ABR), router R2, the no-summary keyword is required with the area stub command to create a totally stubby area. All other routers in area 5 will require the stub command without the no summary keyword. The following commands are required to configure R2:

R2(config)# router ospf 5
R2(config-router)# area 5 stub no-summary
R2(config-router)# network 172.31.200.0 0.0.7.255 area 5

R1 will require:

R1(config)# router ospf 5
R1(config-router)# area 5 stub
R1(config-router)# network 172.31.200.0 0.0.7.255 area 5

All routers within a stub area must be configured as stub, or adjacencies will not form. Besides the command to enable OSPF and the command to identify the area, the only other required command identifies the area as a stub. A totally stubby area does not accept any external network LSAs (Type 5) or any inter-area summary LSAs (Types 3 and 4) from entering the area.

Use the area stub command with the no-summary keyword to configure a totally stubby area. The diagram below shows the commands that should be executed on R1 and R2.

300-410 Part 03 Q04 033

300-410 Part 03 Q04 033

The correct syntax for the area stub command is shown below:

Router(config-router)# area area-id stub [no-summary]

Note that the optional no-summary keyword is used only on area border routers (ABRs) to block summary link advertisements into the stub area. This option creates a totally stubby area. It is very important to configure the command consistently on all routers within the area. OSPF sends its stub status (on or off) in its hello packets. If two neighbors have conflicting stub status, they will not form an adjacency, and you end up with no OSPF communication over that link.

Objective:
Layer 3 Technologies
Sub-Objective:
Configure and verify network types, area types, and router types

Leave a comment