OSPF LSA Types Explained 11 Types of LSA in OSPF!

OSPF LSA Types is the first topic you need to understand if you are trying to understand OSPF routing protocol. There are 11 different types of LSA in OSPF and we will look at each one of them, why do we have many different LSA in OSPF, we will discuss the topologies and the examples to make it more clear for everyone.

What is LSA in OSPF?

We should start asking the most fundamental question first about OSPF. What is LSA? LSA stands for Link State Advertisement and it carries, prefix information, interface cost, if advanced technologies such as Traffic Engineering are enabled, can carry link color information, used bandwidth, available bandwidth, and so on.

When a router receives an LSA, it is stored in the Link State Database (LSDB) of OSPF. Once the LSDBs between the routers are synchronized,

OSPF uses the SPF/Dijkstra algorithm to calculate the best path for each destination network. OSPF LSAs are information about a route that is transported inside OSPF Link State Update (LSU) packets.

We can only have scalable, resilient, fast-converged OSPF design when we understand OSPF LSAs and Area types and their restrictions

Different LSA Types is OSPF v2

Figure -11 Different LSA Types is OSPF v2

OSPF LSA Type 1 - OSPF Router LSA

OSPF Type 1 LSA/Router LSA packets are sent between routers within the same OSPF area and do not leave the area.

An OSPF router uses Type 1 LSA to describe its own interfaces but also carries information about its neighbors to adjacent routers in the same area.

OSPF Type 1 LSA is created by each and every router in a given OSPF area, as we will see in the other LSA types, some of them are only created by special types of routers.

When the OSPF Prefix suppression type of feature is used, infrastructure prefixes are removed from Type 1 LSA, so OSPF scalability can be achieved.

OSPF LSA Type 2 - OSPF Network LSA

OSPF Type 2 LSA/Network LSA packets are generated by the OSPF Designated Router (DR) to describe all routers connected to its segment directly.

Type 2 LSA is flooded between neighbors in the same OSPF area and doesn't cross the area boundary.

Type 2 Network LSA is not desired if the OSPF connection is a point-to-point. Because there are only two points, no need for a DR/BDR election and also no need for extra Type 2 LSA. Type 2 LSA will be stored in OSPF LSDB and Routing table and their size will grow unnecessarily if the connection type is a point to point.

We want DR/BDR election, thus Network LSA, only if the connection model is Multi-access. This means that in the segment, many OSPF routers are attached.

Although it should be the subject of another post, let me just say here that, having DR/BDR election increases network convergence time. So, no Type 2/Network LSA unnecessarily!.

OSPF LSA Type 3 - OSPF Summary LSA

OSPF Type 3 LSA/Summary LSA packets are generated by the OSPF Area Border Routers (ABR) to summarize its directly connected OSPF area, and advertise inter-area router information to other areas to the ABR is connected.

Type 3 LSA is only seen when there is a hierarchical OSPF network design, meaning an OSPF Multi-area network design.

If there is only one OSPF area in the network, we can't have Type 3 LSA.


OSPF Type 4 LSA/ASBR Summary LSA is used to advertise the presence of an Autonomous System Border Router - ASBR in other areas.

Inside the same area that we have an ASBR, ASBR reachability is achieved with OSPF Type 1 LSA.

If there is Type 5 LSA, and if there is Hierarchical OSPF Network design, meaning OSPF Multi-area network design, then we can have OSPF Type 4 LSA. Otherwise, as it is said above, ASBR reachability is achieved via Type 1 LSA in a single area OSPF network design.

OSPF LSA Type 5 - OSPF ASBR External LSA

OSPF Type 5 LSA/ASBR External LSA in OSPF LSA Types is generated by the ASBR to advertise external redistributed prefixes into the OSPF domain.

These external routes/prefixes are redistributed into the OSPF network by the ASBR and seen as either E1 or E2 entries in the routing tables of the routers.

External LSA is domain-wide, meaning if we redistribute prefixes into OSPF, those redistributed prefixes are flooded everywhere, even if there are multiple areas in OSPF, every area receives them. Exceptions are Stub Area and its variations, such as Totally Stub Area, NSSA, and Totally NSSA Area.

OSPF LSA Type 6 - OSPF Group Membership LSA

OSPF Type 6 LSA was considered for the Multicast purpose, Multicast routing for OSPF but never implemented or deployed. Similar to the DVMRP protocol, it didn't last long and today for IP Multicast routing purpose, PIM - Protocol Independent Multicast is used. Although Type 6 LSA is not used, when we cover OSPF LSA Types, it was necessary to explain it too.

OSPF LSA Type 7 - OSPF Not So Stubby Area (NSSA) External LSA

OSPF Type 7 LSA/NSSA External LSA is seen in NSSA and Totally NSSA Areas when there is redistribution.

Normally Stub Areas don't allow redistribution, but as a Not So Stubby Area (NSSA), redistribution is allowed. But, redistributed prefixes are not seen as Type 5 LSA, they are seen as Type 7 LSA.

Type 7 LSA is translated to Type 5 LSA to be sent into the OSPF Area 0/Backbone Area.

If there are two NSSA ABRs, they negotiate with each other and the NSSA ABR with the lower Router ID does the translation.

OSPF LSA Type 8 - OSPF External Attributes LSA

Normally BGP prefixes are redistributed into OSPF or any other routing protocol, and BGP attributes are lost. But, you may need to carry BGP attributes with your Autonomous System between the Routers.

Let's say, for the given destination IP prefix, you have two exit points from your network, and for the outbound direction, you want to prefer one of those exit points as Primary. You can use this BGP Local Preference attribute.

Two Routers exchange the prefixes with each other, and when they check the BGP Local Preference attribute, which every Router has the higher Local Preference, that router is used as an exit point by both of the routers.

But BGP local preference e attributes cannot be carried in OSPF normally. Because of reachability, you need to redistribute from BGP to OSPF, and if you redistribute, attributes are lost.

Type 8 LSA in OSPF LSA Types, was considered for this purpose. BGP Attributes would be carried even if we would redistribute. But yet another LSA that we don't use in computer networking. Instead of this LSA, IBGP - Internal BGP is used in the networks. Hope Type 8 LSA as one of the OSPF LSA Types is understood better now.

OSPF LSA Type 9, 10, 11 - OSPF Link Scope Opaque LSA

Opaque LSAs LSA Type 9, 10, and 11 are used to extend the capabilities of OSPF.

With these LSA Types, OSPF carries many other protocol capabilities. For example, RSVP Traffic Engineering and Segment Routing Traffic Engineering requires topology information, used bandwidth, available bandwidth, reserved bandwidth, link coloring information, delay or other attributes, and so on.

BIER - Bit Indexed Explicit Replication, the newest and most scalable Multicast architecture information is conveyed with Opaque LSAs as well. OSPF Graceful Restart/GR and many other use cases we have with Opaque LSAs. Think of it as a helper to the basic OSPF mechanism. In addition to carrying prefixes and cost, much other information can be carried with them. Type 9 LSA is link scope, Type 19 is Area scope and Type 11 is AS scope Opaque LSAs.

What type of OSPF LSA is originated by ASBR routers to advertise external routes?

Let's review what we have learned. The answer to this question is Type 5 External LSA. ASBR advertises external routes as Type 5 LSA and this LSA is flooded in every area in the OSPF domain if they are not Stub or NSSA.

What information is contained within an OSPF type 4 LSA?

Type 4 LSA is used for ASBR reachability as t was explained earlier in the post as well. But, it is seen only if there is a multi-area OSPF network. In a single area OSPF network design, ASBR reachability is achieved with ASBR's Type 1 LSA.

OSPF LSA types are in general used for OSPF Scalability. Only with 1 LSA type, all the information could be carried. But when we have multiple areas, for hierarchy, we use different LSAs, as different LSAs have different duties. Understanding their restrictions and which one is allowed in which OSPF Area Types is very important to understand OSPF.

Created by
Orhan Ergun

Orhan Ergun, CCIE/CCDE Trainer, Author of Many Networking Books, Network Design Advisor, and Cisco Champion 2019/2020/2021

He created OrhanErgun.Net 10 years ago and has been serving the IT industry with his renowned and awarded training.

Wrote many books, mostly on Network Design, joined many IETF RFCs, gave Public talks at many Forums, and mentored thousands of his students.  

Today, with his carefully selected instructors, OrhanErgun.Net is providing IT courses to tens of thousands of IT engineers. 

View profile

Daniel Lardeux
Daniel Lardeux Senior Network Consultant at Post Telecom

I passed the CCDE Practical exam and Orhan’s CCDE course was very important contributor to my success. I attended the CCDE course of Orhan Ergun in July and it was exactly what I needed, Orhan is taking the pain to break down the different technologies.

Roy Lexmond
Roy Lexmond Senior Network Designer at Routz CCDE #20150017 & CCIE R&S; #26557

After I attended Orhan Ergun’s CCDE course I passed the CCDE practical exam.I really enjoyed the course a lot ...

Nicholas Russo
Nicholas Russo Network Consulting Engineer (CCDE/CCIEx2), Cisc

I signed up for Orhan’s CCDE training. This training is very technically detailed and the use-cases, quizzes, scenarios, and mind maps are all great resources in the overall training program. Orhan teaches his students to think like a network designer ...

Slide Heading
Slide Heading Network Systems Engineer at Conscia A/S CCIE #42544 (SP) & CCDE #20160015

Orhan is forcing you to take off the implementation hat that most of us have been wearing for many years, instead he is providing a new fancy design hat, which makes you see and deal with the issues presented ...

Kim Pedersen
Kim Pedersen CCIE in RS and SP (#29189) CCDE#20170021

I’ve used Orhan’s self-paced CCDE training material. If you are interested in knowing how all the technologies go together in a coherent design i can highly recommend it.I also enjoyed the Quizzes which helped pick out my weak spots in selecting ...

Laurent Metzger
Laurent Metzger 3xCCIE/CCDE Senior Network Architect

Hi Orhan. I passed the CCDE exam on February 22. I read everything that you put on your Self Paced CCDE Training course and it was very helpful in my success. Thank you very much.

Martin J. Duggan
Martin J. Duggan Network Architect at AT&T;, Ciscopress Author CCDE #20160006 & CCIE#7942

I attended Orhan’s April 201610 days CCDE Bootcamp. I am CCDE now !

You can tell Orhan has a great deal of experience, it really comes through when he presents his design case studies and the CCDE Practical scenarios.

Muhammad Abubakar
Muhammad Abubakar Lead Network Architect – CCDE #20160016 2xCCIE #26693 2xJNCIE VCIX

Your excellent CCDE materials and amazing Bootcamp helped me tremendously through my learning journey.Also thank you very much for being available whenever I have a design question or a complex design topics. I can’t compare your design skills ...

Jennifer Pai
Jennifer Pai Network/Security Engineer at KNET Technology

Thanks Orhan very much for this course. It helped strengthen my “Network design mind”.

Ruslan Silyayev
Ruslan Silyayev Solution Architect at R.I.S.K Company

Training by Orhan is not a CCDE preperation training only. It will be useful for engineers which are dealing with design. You want to pass CCDE exam or learn network design, then don’t look at anywhere else!

Sameer Meher
Sameer Meher Solutions Architect at 23 Wards/Japan

Orhan Ergun’s CCDE course was really very good. CCDE Level Intelligence was delivered very well and with very useful case studies and the scenarios, I am thankful to Orhan for all his help!

Ken Young
Ken Young Senior Technical Architect Province of Nova Scotia, 2xCCIE #41597 | CCDE #20170047

If anyone wants to understand network design and architecture, also pass CCDE exam , I recommend you to attend Orhan’s online courses! I am a CCDE now but learning is a journey, we will be together in your other courses too Orhan!

Matt Cross
Matt Cross Technical Architect at Heartland – CCDE #2019::7

Orhan did an excellent job of filling in the gaps of knowledge that I had that took me to the finish line of the practical exam CCDE. The community of people that Orhan facilitates are both engaging and supportive of the journey to CCDE. Orhan ...

Shiling Ding
Shiling Ding Sentinel Technologies – CCDE #2019::12

Just passed the CCDE Practical exam! I attended Orhan Ergun’s CCDE training program , used Orhan’s Instructor Led and Self-Paced CCDE training and Online CCDE Practical Scenarios during my CCDE journey. Orhan’s CCDE In Depth book is an excellent summary ...

Abelardo Basurto
Abelardo Basurto Solutions Architect at Cisco Systems – CCDE 2018::6

Hi everyone, I’ve just passed the CCDE Exam. My Number is CCDE 2018::6 I attended to Online CCDE Bootcamp of Orhan. I want to thank Orhan not only for the great book and bootcamp, but also for his commitment, availability and willingness to assist the ...

Hady Mohamed Abdellah
Hady Mohamed Abdellah Network Architect Hamad International Airport Qatar – CCDE 2018::1

Hi guys, I’m so happy that I passed the exam. I’ve already got my number CCDE 2018::1. Thanks to Orhan for being the best CCDE instructor in the world. I highly recomend Orhan’s CCDE Training and In-Depth-CCDE ...

Bryan Bartik
Bryan Bartik Sr. Systems Engineer at CompuNet – CCDE 20170059

Hi Orhan I passed CCDE Practical exam on November 2017 ! I really enjoyed your materials and quizzes and use cases. They were definitely helpful in my preparation. Thanks a lot !

Giedrius Trapkauskas
Giedrius Trapkauskas Network Solutions Architect at Liberty Global – CCDE 20180004

I attended Orhan’s CCDE Training in Istanbul and it was very helpful in my preparation. I passed the exam recently and I want to say Thank you Orhan! For those who want to pass the CCDE exam, definitely start with ...

Alaa Issa
Alaa Issa Sr.Solutions Architect – CCDE#20180033 3xCCIE ( Collab|DC|Security )#27146

I registered to Orhan’s training in Feb 2017. From that time, I attended Orhan’s training several times. The depth of knowledge which Orhan has is amazing, and how to present such consistent knowledge to the ...

Mazin Ahsan Design Lead Engineer | Solutions Engineer | CCDE License # 20160030 | CCIE Licence # 23892

I passed the CCDE Practical Lab exam on November 17,2016 from supplications of elders and dedication from my Sensei Mr. Orhan Ergun I took different CCDE bootcamps in the past. Orhan has the most depth and expertise ...

Jeff Patterson CCDE# 2018::11

Hi Orhan I wanted to pass along my appreciation for the outstanding training material. I used the online CCDE training provided by Orhan as well as the In-Depth-CCDE book and passed the exam in February 2018. Thank you Orhan!

Mehdi Sfar
Mehdi Sfar Network and Security Architect / CCDE #20210003 | CCIE R&S; #51583

I signed up for Orhan’s CCDE Self paced Course. This course, along with the CCDE In Depth book, helped me for my CCDE Practical as well as Written exams. It pushed me to ask the "WHY" questions and allowed ...

Related courses

OSPF Training

06:18:51 Hours
26 Lectures


IS-IS Training

05:14:41 Hours
12 Lectures


Routing Protocols Design and Deployment Course

47:00:55 Hours
51 Lectures