OSPF Network Loopback

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Pic. 1 - Topology Diagram.

Task 1

On R1 create loopback 1 interface with the address 1.1.1.1/24. Advertise this subnet into OSPF area 13 and ensure other OSPF routers receive it with the network mask configured on R1 (/24).

Questions

Try to answer the following questions:

1. What is the default network mask of loopback network when advertised into OSPF?
2. How can you advertise loopback network with its actual network mask?

Lab Solution

Solution configuration below:
https://docs.google.com/file/d/0BwE5C95tpjZOWEFGdmtGYWhZbmc/edit?usp=sharing

Task 1

On R1 create loopback 1 interface with the address 1.1.1.1/24. Advertise this subnet into OSPF area 13 and ensure other OSPF routers receive it with the network mask configured on R1 (/24).

R1 Config:
!
interface Loopback1
 ip address 1.1.1.1 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 13
!

Notice!
The statement 'ip ospf network point-to-point' allows OSPF to advertise loopback network with the actual (configured) network mask

Study Drill

Check ip ospf database to see what the  loopback interfaces (e.g. 10.0.1.1). Compare this output with the 1.1.1.0/24 loopback network you have configured in the lab solution. Use 'show ip ospf database router' on R1

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� Jarek Rek 2013