What is Stub Area in OSPF?
The Stub Area is a special type of area in the Open Shortest Path First (OSPF) routing protocol that is configured to minimize the amount of route information exchanged between the core OSPF network and the edge devices. The Stub Area has typically been used in a small office or home office (SOHO) deployments where it is not necessary to exchange routing information with the outside world.
Benefits of Stub Area
There are several benefits to configuring a Stub Area in OSPF:
1. Reduces the amount of routing information exchanged between devices, which can lead to improved network performance.
2. Helps to improve network security by reducing the visibility of the internal network topology.
3. Makes it easier to configure and manage OSPF in small networks.
Can a stub OSPF connect to two different areas?
Yes, a stub OSPF can be connected to two different areas. However, it is important to note that the router will only exchange routing information with the core OSPF network, and not with any other devices in the Stub Area. This means that the router will not be able to route traffic between the two areas.
Can Backbone Area be a Stub Area?
No, the Backbone Area cannot be configured as a Stub Area. This is because the Backbone Area is responsible for exchanging routing information between all of the other areas in the OSPF network. If the Backbone Area was configured as a Stub Area, this would prevent routing information from being exchanged between the other areas, which would cause problems with network connectivity.
What is the Default Route in Stub Area?
The Default Route is a special type of route that is used to send all traffic that is not destined for a specific network or host out of the Stub Area. The Default Route is typically configured on the edge devices in the Stub Area so that they can reach devices outside of the area.
Configuring the Default Route
There are two ways to configure the Default Route in a Stub Area:
Static Default Route: The Static Default Route is configured manually on each device in the Stub Area. This method is typically used in small networks where there are only a few devices.
Dynamic Default Route: The Dynamic Default Route has learned automatically from the core OSPF network. This method is typically used in larger networks where there are many devices.
Which LSA are allowed in the Stub Area?
Only the following LSAs are allowed in a Stub Area:
Type 1 LSA (Router LSA): This LSA is generated by each router and contains information about the router’s interfaces and links.
Type 2 LSA (Network LSA): This LSA is generated by each router and contains information about the networks that are attached to the router.
Type 3 LSA (Summary LSA): This LSA is generated by the ABR and contains information about routes that are reachable from the Stub Area.
Can ABR Router be a Stub Area Router?
No, the ABR Router cannot be configured as a Stub Area Router. This is because the ABR Router is responsible for exchanging routing information between the core OSPF network and the Stub Area. If the ABR Router was configured as a Stub Area Router, this would prevent routing information from being exchanged between the two areas, which would cause problems with network connectivity.
Can two Stub Areas be connected?
No, two Stub Areas cannot be connected. This is because the Default Route is used to send all traffic that is not destined for a specific network or host out of the Stub Area. If two Stub Areas were connected, this would cause a routing loop where traffic would keep getting sent between the two areas without ever reaching its destination.
How to Configure Stub Area in OSPF
Here are the steps to configure a Stub Area in OSPF:
1. Configure the router ID.
2. Configure the interfaces.
3. Configure the area type.
4. Configure the default route.
5. Verify the configuration.
These steps are typically performed using a text-based console interface, such as the Cisco IOS command-line interface (CLI).
Example:
Router(config)# router OSPF
Router(config-router)# router-id 1.1.1.1
Router(config-router)# network 10.0.0.0 0.255.255.255 area 0
Router(config-router)# area 0 stub
Router(config-router)# default-information originate
In this example, the router ID is configured as 1.1.1.1, the interfaces are configured to use the 10.0.0.0/24 network, and the area type is set to a stub. The default route is also configured to be originated from this router.