What is the Backbone Area of OSPF?
The Backbone Area is the central area of an Open Shortest Path First (OSPF) network, and all other areas are connected to it. The Backbone Area is also known as Area 0. All OSPF routers must be members of the Backbone Area.
The Backbone Area is the most important area in an OSPF network. It is responsible for routing traffic between all the other areas in the network. Without the Backbone Area, OSPF would not be able to function properly.
The Backbone Area is also responsible for generating LSAs (Link State Advertisements). LSAs are used by OSPF to build its routing table. The router with the best path to the destination is chosen as the next hop.
Why Backbone Area is Required in OSPF?
The Backbone Area is required in OSPF for two main reasons:
1. To provide a common routing infrastructure for all the other areas in the network.
2. To generate LSAs, which are used by OSPF to build its routing table.
Relationship Between Area 0 and AS in OSPF
The Backbone Area is similar to an Autonomous System (AS) in OSPF. An AS is a group of OSPF routers that share the same routing policy. The Backbone Area is like an AS because all the other areas in the network are connected to it, and it has its own LSAs.
There are some important differences between the Backbone Area and an AS.
- The Backbone Area is always part of Area 0, which is the default area for all OSPF routers.
- The Backbone Area cannot be stub or totally stubby.
- The Backbone Area does not have a routing table. All the other areas in the network have their own routing tables, which are built using the LSAs generated by the Backbone Area.
Relationship Between Backbone Area and Virtual link in OSPF
A virtual link is an imaginary link between two OSPF routers that are not physically connected. Virtual links are used to connect two parts of an OSPF network that are not physically connected.
The Backbone Area cannot be a virtual link. A virtual link can only be created between two areas that are not part of the Backbone Area.
Backbone Area Terminology
There are some important terms that are used to describe the Backbone Area:
Router: A router is a device that forwards traffic between two or more networks.
LSA: A Link State Advertisement (LSA) is a message that is sent by OSPF routers to advertise their links to other OSPF routers.
LSA Type: There are different types of LSAs, and each type has a different function.
Link: A link is a connection between two OSPF routers.
Area: An area is a group of OSPF routers that share the same LSAs.
AS: An Autonomous System (AS) is a group of OSPF routers that share the same routing policy.
Can We Change the Backbone Area in OSPF?
The Backbone Area cannot be changed. All OSPF routers must be members of the Backbone Area.
The only way to change the Backbone Area is to delete all the other areas in the network, which would effectively make the Backbone Area the only area in the network.
How to Configure Backbone Area in OSPF?
The Backbone Area is configured automatically when OSPF is enabled on a router. There is no need to configure the Backbone Area manually.
When OSPF is enabled on a router, the router becomes a member of the Backbone Area and starts generating LSAs.
If you want to change the configuration of the Backbone Area, you can do so by deleting all the other areas in the network. This will effectively make the Backbone Area the only area in the network.
Deleting all the other areas in the network is not recommended, as it will cause OSPF to stop working properly.
Here are the commands to configure the Backbone Area:
1. Enable OSPF on the router.
2. Configure the router ID.
3. Assign an IP address to the loopback interface.
4. Configure the OSPF area type.
5. Specify the networks that should be included in the OSPF area.
6. Redistribute static routes into OSPF.
7. Save the configuration.
Example:
- Router(config)# router OSPF
- Router(config-router)# router-id 1.1.1.1
- Router(config-router)8 loopback 0
- Router(config-if)$ IP address 10.0.0.1 255.255.255.0
- Router(config-if)# exit
- Router(config-router)$ network 10.0.0.0 255.255.255.0 area 0
- Router(config-router)$ redistribute static
- Router(config-router)$ exit
- Router(config)# copy running-config startup-config
The above example shows how to configure the Backbone Area on a router. The router ID is 1.1.1.1, and the loopback interface has been assigned the IP address 10.0.0.1/24. The OSPF area type is set to 0, which is the Backbone Area. The network 10.0.0.0/24 is included in the OSPF area.