What is NSSA Not So Stubby Area in OSPF?
Not So Stubby Area (NSSA) is a type of Open Shortest Path First (OSPF) area that allows for limited advertisement of external routes. NSSA was designed to address the problem of stub areas, which do not allow for the exchange of external routes. However, NSSA has some limitations compared to other types of OSPF areas.
NSSA is sometimes also referred to as a “narrow” or “restricted” stub area.
Benefits of Not So Stubby Area (NSSA)
- It allows for the advertisement of a default route into the stub area. This is accomplished by configuring a default route in the NSSA area, which is then advertised to other areas. This allows for better connectivity and reachability within the network.
- It allows for the advertisement of Type 7 LSAs. Type 7 LSAs are external route advertisements that originated from ASBRs within the NSSA area. This allows for more information to be exchanged between different areas, which can be beneficial for network administration and troubleshooting purposes.
Drawbacks of Not So Stubby Area (NSSA)
- It does not support the exchange of Type 5 LSAs. Type 5 LSAs are external route advertisements that originated from ASBRs outside of the NSSA area. This means that any external routes that need to be advertised in the NSSA area must be done so manually, which can be time-consuming and error-prone.
- It uses a different routing table than other types of OSPF areas. This can make it more difficult to configure and manage NSSA areas, especially in larger networks.
- NSSA does not support the use of route summarization. This means that all routes within the NSSA area must be advertised individually, which can lead to increased network traffic and decreased performance.
Can a Not So Stubby Area OSPF connect to two different areas?
Yes, a Not So Stubby Area (NSSA) can be connected to two different areas. This is accomplished by configuring a default route in the NSSA area, which is then advertised to other areas. This allows for better connectivity and reachability within the network.
Can Backbone Area be a Not So Stubby Area?
No, a Backbone Area cannot be a Not So Stubby Area (NSSA). This is because the Backbone Area must support the exchange of Type 5 LSAs, which are external route advertisements that originated by ASBRs outside of the NSSA area. The NSSA area does not support the exchange of these LSAs, which means that the Backbone Area cannot be an NSSA.
What is the Default Route in Not So Stubby Area?
The Default Route in the Not So Stubby Area (NSSA) is a route that is configured in the NSSA area and then advertised to other areas. This allows for better connectivity and reachability within the network. The Default Route is also sometimes referred to as the “Default Gateway” or “Default Router.”
Configuring the Default Route in Not So Stubby Area
The Default Route can be configured in the NSSA area by using the “default-information originate” command. This command will cause the router to advertise a default route into the NSSA area. The default route will be advertised with a metric of 20.
How to Configure Not So Stubby Area in OSPF?
Here are the steps to configure the Not So Stubby Area (NSSA) in Open Shortest Path First (OSPF):
Step 1: Configure the router ID.
Step 2: Configure the OSPF process ID.
Step 3: Enable OSPF on all interfaces that will be part of the NSSA area.
Step 4: Configure the NSSA area ID.
Step 5: Configure the default route.
Step 6: Configure any other desired OSPF parameters.
After completing these steps, the NSSA area will be up and running.
Example:
Router(config)# router OSPF 1
Router(config-router)# router-id 1.1.1.1
Router(config-router)# area 1 nssa
Router(config-router)# default-information originate
Which LSA are allowed in the Not So Stubby Area?
Type 7 LSAs are allowed in the Not So Stubby Area (NSSA). Type 7 LSAs are external route advertisements that originated from ASBRs within the NSSA area. This allows for more information to be exchanged between different areas, which can be beneficial for network administration and troubleshooting purposes.
Can ABR Router be a Not So Stubby Area Router?
No, an ABR Router cannot be a Not So Stubby Area (NSSA) Router. This is because the ABR Router must support the exchange of Type 5 LSAs, which are external route advertisements that originated by ASBRs outside of the NSSA area. The NSSA area does not support the exchange of these LSAs, which means that the ABR Router cannot be an NSSA.
Can two Not So Stubby Areas be connected?
Yes, two NSSA areas can be connected. This is accomplished by configuring a default route in each NSSA area, which is then advertised to the other area. This allows for better connectivity and reachability between the two areas.