OSPF Area Types Explained: Stub, Totally Stubby & NSSA with CLI, Lab & Real-World Use Cases [CCNP ENTERPRISE]

If you’ve ever felt confused by OSPF area types—like what makes an area “Stub,” “Totally Stubby,” or “NSSA”—you’re not alone. Many of my CCNP Enterprise trainees get tripped up on these terms, especially when it comes to LSA propagation and route filtering across areas.

That’s why in this guide, we’ll break it all down in a simple, real-world way. Whether you’re prepping for a certification exam or building a scalable enterprise network, understanding OSPF area types will help you optimize performance, reduce unnecessary routing data, and design smarter networks.

Let’s simplify the theory, hit some CLI, do a real EVE-NG lab, and wrap it up with practical FAQs. Ready?

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Theory in Brief – What Are OSPF Area Types?

OSPF is a link-state protocol that breaks networks into areas to manage topology complexity. But not all areas are equal—some are restricted to reduce routing overhead or control what kind of LSAs are allowed.

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Standard Area

This is the default OSPF area. It allows all LSA types including external routes (Type 5).

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Stub Area

A Stub Area does not allow Type 5 LSAs (external routes like BGP). Instead, a default route is injected by the ABR.

Benefit: Reduces database size by blocking external LSAs.

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Totally Stubby Area

Even more restrictive than a stub—no Type 3, 4, or 5 LSAs are allowed. Only a default route is injected.

Cisco-proprietary using.

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NSSA (Not-So-Stubby Area)

Allows internal OSPF routes and external route redistribution, but Type 5 LSAs are blocked. Instead, Type 7 LSAs are generated and translated to Type 5 by the ABR.

Great for edge locations that need to redistribute into OSPF without overwhelming the core.

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Comparison of Area Types

Area Type	Allows Type 3	Allows Type 5	Allows Type 7	External Redistribution	Use Case
Standard	Yes	Yes	No	Yes	Backbone and core areas
Stub	Yes	No	No	No	Leaf area with no redistribution
Totally Stubby	No	No	No	No	Most restricted leaf area
NSSA	Yes	No	Yes	Yes	Redistribution at edge sites
Totally NSSA	No	No	Yes	Yes	Edge site with only default route

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Essential CLI Commands

Task	Command	Description
Check area types	show ip ospf	View areas and their configuration
Verify LSAs per area	show ip ospf database	Check which LSA types are seen per area
Configure stub area	area 1 stub	Basic stub configuration
Configure totally stubby area (Cisco)	area 1 stub no-summary	Blocks even summary LSAs
Configure NSSA	area 2 nssa	Enables NSSA area
Totally NSSA (Cisco)	area 2 nssa no-summary	Blocks Type 3 LSAs in NSSA
Verify external LSA filtering	show ip route ospf	Ensures only internal/default routes appear
View redistributed routes	show ip ospf database external	Check for Type 5 LSAs
View NSSA external LSAs	show ip ospf database nssa-external	Type 7 LSA visibility

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Real-World Use Cases

Scenario	Area Type Used	Why It Works
Remote branch with no external networks	Totally Stubby	Simplifies routing; gets just default route
Hub-and-spoke design with central BGP	Stub	Prevents unnecessary Type 5 LSAs to branch routers
Branch needs to redistribute static	NSSA	Allows static routes in without flooding backbone with Type 5
Provider-managed customer edge router	Totally NSSA	Filters inter-area and external LSAs but allows redistribution

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EVE-NG Lab – OSPF Stub, NSSA Configuration

Objective:

• Build OSPF areas: Standard, Stub, Totally Stubby, and NSSA
• Observe how LSAs are filtered
• Redistribute static routes in NSSA

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Topology Diagram

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Configuration Snippets

R2 (ABR):

router ospf 1
 network 10.0.0.0 0.0.0.255 area 0
 network 10.1.0.0 0.0.0.255 area 1
 network 10.2.0.0 0.0.0.255 area 2

R3 (Stub):

router ospf 1
 network 10.1.0.0 0.0.0.255 area 1
 area 1 stub

R4 (NSSA + ASBR):

router ospf 1
 network 10.2.0.0 0.0.0.255 area 2
 area 2 nssa
 redistribute static subnets

Optional Static Route on R4:

ip route 192.168.1.0 255.255.255.0 null0

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Testing:

• On R3, check show ip route to verify only default route is seen.
• On R1, see if redistributed route from R4 appears (Type 5 via ABR).
• Use show ip ospf database to check LSA types per area.

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Troubleshooting Tips

Problem	Likely Cause	Fix
External routes seen in stub area	Incorrect area type	Confirm area config on both routers
No redistribution in NSSA	ABR not converting Type 7 to 5	Make sure ABR is properly configured
Routes missing from R3 (Stub)	No default route injected	Ensure ABR is set to inject default into stub
R4 routes not propagating	redistribute static not working	Check for route maps or missing static routes
Type 5 LSA present in NSSA	Area not declared as NSSA	Reconfigure area with area X nssa

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FAQs – OSPF Area Types (Stub, NSSA)

1. What is an LSA in OSPF, and why is it important?

Answer:
An LSA (Link-State Advertisement) is the fundamental building block in OSPF that carries information about routers, links, networks, and topology. Each OSPF router generates LSAs, and they are flooded within the OSPF area to build the Link-State Database (LSDB). The router then uses the SPF (Dijkstra) algorithm to calculate the shortest path tree and install routes in the routing table.

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2. How many types of LSAs are there in OSPFv2, and are they all used in every network?

Answer:
OSPF defines 11 LSA types in total, but not all are used in every network. The most commonly used are:

• Type 1 – Router LSA
• Type 2 – Network LSA
• Type 3 – Summary LSA
• Type 4 – ASBR Summary LSA
• Type 5 – External LSA
• Type 7 – NSSA External LSA

Other types like Type 6, 8, 9, 10, and 11 are either reserved, used for special functions (like multicast or opaque LSAs), or used in specific topologies.

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3. What is a Type 1 LSA (Router LSA)?

Answer:
A Type 1 LSA is generated by every router within an area and contains information about the router’s directly connected interfaces, links, and their states. It is flooded only within the area. This LSA helps routers within the same area understand the internal topology.

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4. What is a Type 2 LSA (Network LSA), and when is it used?

Answer:
A Type 2 LSA is generated by the Designated Router (DR) on a multi-access network segment (like Ethernet). It advertises the routers connected to that multi-access segment. This LSA helps reduce LSA flooding and optimizes SPF calculations by representing a shared network as a pseudo-node.

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5. What is a Type 3 LSA (Summary LSA), and how does it function across areas?

Answer:
A Type 3 LSA is generated by an ABR (Area Border Router) and advertises networks from one area into another. It allows inter-area communication in a multi-area OSPF topology. These LSAs do not carry full topology but just route information, helping OSPF scale across large networks.

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6. What is a Type 4 LSA (ASBR Summary LSA), and why is it needed?

Answer:
When an ASBR (Autonomous System Boundary Router) is present (which redistributes external routes), Type 4 LSAs are generated by ABRs to inform other areas how to reach that ASBR. This LSA provides a path to reach the ASBR before Type 5 external routes can be used.

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7. What is a Type 5 LSA (External LSA)?

Answer:
A Type 5 LSA is generated by an ASBR to advertise external routes (from other routing protocols like BGP, EIGRP, or static). It is flooded throughout the OSPF domain, except for stub areas. Type 5 LSAs support both Type 1 (E1) and Type 2 (E2) external routes.

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8. What is a Type 7 LSA, and where is it used?

Answer:
A Type 7 LSA is used only in NSSA (Not-So-Stubby Area). It is generated by an ASBR inside an NSSA to advertise external routes. ABRs then translate it into a Type 5 LSA when it leaves the NSSA and enters a normal OSPF area.

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9. How can I view LSA types on a Cisco router using CLI?

Answer:
Use the following command to view the LSAs in the LSDB:

show ip ospf database

To view a specific LSA type, append the type:

show ip ospf database router
show ip ospf database network
show ip ospf database summary
show ip ospf database external

This gives insights into how LSAs are structured and propagated across areas.

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10. What are the main differences between Type 5 and Type 7 LSAs?

Answer:

Feature	Type 5 LSA	Type 7 LSA
Used In	Standard OSPF Areas	NSSA Areas
Generated By	ASBR	ASBR within NSSA
Flood Scope	Throughout OSPF domain	Within NSSA only
Translated By	Not Translated	Translated to Type 5 by ABR
Acceptable in Stub?	Not allowed in Stub Areas	Allowed in NSSA

Understanding this difference is key when designing OSPF areas and applying route redistribution strategies.

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YouTube Link

Watch the Complete CCNP Enterprise: OSPF Area Types Explained: Stub, Totally Stubby & NSSA with CLI, Lab & Real-World Use Cases Lab Demo & Explanation on our channel:

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Final Note

Understanding how to differentiate and implement OSPF Area Types is critical for anyone pursuing CCNP Enterprise (ENCOR) certification or working in enterprise network roles. Use this guide in your practice labs, real-world projects, and interviews to show a solid grasp of architectural planning and CLI-level configuration skills.

If you found this article helpful and want to take your skills to the next level, I invite you to join my Instructor-Led Weekend Batch for:

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