Cisco CCNP BSCI Exam Tutorial Using The OSPF Command Area Range
Below is a MRR and PLR article in category Computers Technology -> subcategory Computer Certification.
Cisco CCNP/BSCI Exam Guide: Mastering OSPF Route Summarization
Introduction
Achieving success in the BSCI and CCNP exams requires a deep understanding of OSPF route summarization. This isn't merely a test of your binary skills; it’s about knowing the right time and place to implement summarization. OSPF offers numerous options, making it essential for candidates to master the details.
Route Summarization in OSPF
OSPF provides two main methods for route summarization. Previously, we discussed the "summary-address" command. Today, we'll focus on the "area range" command, crucial for consolidating routes between OSPF areas.
Using the "Area Range" Command
The "area range" command is applied on an Area Border Router (ABR) to aggregate routes advertised from one OSPF area to another. In our example, R1 serves as an ABR with interfaces in both Area 0 and Area 1, where four loopbacks are configured.
```shell
R1(config)
router ospf 1
R1(config-router)network 12.0.0.0 0.255.255.255 area 1
R1(config-router)network 13.0.0.0 0.255.255.255 area 1
R1(config-router)network 14.0.0.0 0.255.255.255 area 1
R1(config-router)network 15.0.0.0 0.255.255.255 area 1
```An OSPF neighbor, R2, initially displays all four routes:
```shell
R2
show ip route ospf
O IA 12.12.12.12 [110/65] via 172.12.123.1, Serial0O IA 13.13.13.13 [110/65] via 172.12.123.1, Serial0
O IA 14.14.14.14 [110/65] via 172.12.123.1, Serial0
O IA 15.15.15.15 [110/65] via 172.12.123.1, Serial0
```
To streamline the routing tables for downstream routers while maintaining connectivity, use the "area range" command on R1:
```shell
R1(config)
router ospf 1
R1(config-router)area 1 range 12.0.0.0 252.0.0.0
```Now, R2 shows a single summary route:
```shell
R2
show ip route ospf
O IA 12.0.0.0/6 [110/65] via 172.12.123.1, Serial0```
Understanding the Null Route
After configuring summary routes, R1’s routing table includes a route to null0:
```shell
R1
show ip route ospf
O 12.0.0.0/6 is a summary, Null0```
When OSPF summary routes are created, a null0 route is automatically added to the summarizing router’s table. This prevents routing loops by ensuring packets destined for the summarized routes take a longer match, while any other packets matching the summary are discarded.
Mastering the "area range" command is vital for both your exams and professional expertise. Understanding its nuances will significantly enhance your network design and troubleshooting skills.
You can find the original non-AI version of this article here: Cisco CCNP BSCI Exam Tutorial Using The OSPF Command Area Range .
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