Category Archives: CCNP

Master the OSPF LSA Types


An Overview of OSPF LSA Types

We know that Link State Advertisements (LSA) are the life blood of an OSPF network. The flooding of these updates (and the requests for this information) allow the OSPF network to create a map of the network. This of course occurs with a little help from Dijkstra’s Shortest Path First Algorithm.

But not all OSPF LSA’s are created equal. In this post, we will examine the different types that are used within the OSPF multi area design. In the very next post here at the blog, we will recap how they are dynamically filtered when we have an OSPF domain that consists of special areas like Stub or Totally Stubby.

The Router (Type 1) LSA

We begin with what many call the “fundamental” or “building block” Link State Advertisement. The Type 1 LSA (also known as the Router LSA) is flooded within an area. It describes the interfaces of the local router that are participating in OSPF and the neighbors the local OSPF speaker has established.

The Network (Type 2) LSA

Do you remember how OSPF functions on an Ethernet (broadcast) segment? It elects a Designated Router (DR) and Backup Designated Router (BDR) in order to reduce the number of adjacencies that must be formed and the chaos that would result from a full mesh of these relationships. Well, the Type 2 LSA is sent by the Designated Router into the local area. This LSA describes all of the routers that are attached to that Ethernet segment.

The Summary (Type 3) LSA

Ready for a big difference with this LSA type? Recall that your Type 1 and Type 2 LSAs are sent within an area. We call these intra-area LSAs. Now it is time for the first of our inter-area LSAs. The Summary (Type 3) LSA is used for advertising prefixes learned from the Type 1 and Type 2 LSAs into a different area. Do you recall what device would send such an LSA? Sure, it would be the Area Border Router that separates areas.

So let’s say we have an area design like this – AREA 1-AREA 0-AREA 2. The Area 1 ABR would send the Type 3 LSAs into Area 0. It’s ABR into Area 2 would send these Type 3 LSAs into that area to provide full reachability in the OSPF domain. The Type 3 LSAs remain Type 3 LSAs during this journey, it is just OSPF costs and advertising router details that change in the advertisements. Notice also that in this example we are describing a multi area OSPF design that is not using any special area types like Stub or Totally Stubby.

The ASBR Summary (Type4) LSA

Do you recall the very special OSPF router that brings in routes from another domain (like an EIGRP domain)? It is the Autonomous System Boundary Router. In order to inform routers in different areas about the existence of this special router, the Type 4 LSA is used. This Summary LSA provides the router ID of the ASBR. So once again, the Area Border Router is responsible for shooting this information into the next area and we have another example of an inter-area LSA.

The External (Type 5) LSA

So the ASBR is the device that is brining in prefixes from other routing domains. The Type 4 LSA describes this device. But what LSA is used for the actual prefixes that are coming in from the other domain? Yes, you guessed it, it is the Type 5 LSA. The OSPF ASBR creates these LSAs and they are sent to the Area Border Routers for dissemination into the other areas. Remember, this might change if we are using special area types.

The NSSA External (Type 7) LSA

Remember that in OPSF there is a VERY special area type called a Not So Stubby Area. This area can act stub, but it can also bring in external prefixes from an ASBR. You guessed it, these prefixes are sent as Type 7 LSAs. When an ABR gets these Type 7 LSAs, it sends them alone in to the other areas as a Type 5 LSA. So the Type 7 designation is just for that very special NSSA area functionality.

Other LSA Types

Are there other LSA types? You bet there are. But we do not often encounter these. For example, a Type 6 LSA is used for Multicast OSPF and that technology never really caught on, allowing Protocol Independent Multicast to win out.

I hope you enjoyed this recap of the very important LSA types we have in OSPF. This is all detailed and demonstrated further in my latest course on OSPF for CBT Nuggets. I hope you will consider a free week subscription and checking that out. It is garnering rave reviews.

Study with passion my friends!
Cisco Learning Network Store home page

Seven New Courses in Routing and Switching Coming from CBT Nuggets

Routing and Switching


I was thrilled to be tasked with creating new Nuggets on the topic of Enterprise Routing and Switching for Juniper networks. I quickly decided on two important approaches for this new training. First, I decided to break the topic up into seven courses so that I could really go into great detail. Second, I decided to separate these Nuggets clearly on theory, then Juniper specific stuff. This will be great for Cisco, Arista, HP, and other students that want to learn these important technologies, but could care very little for how specifics are carried out on Juniper gear.

The New Routing and Switching Courses:

Here is the breakdown of the new courses:

  • JNCIS-ENT(JN0-343)- Layer 2
  • JNCIS-ENT(JN0-343)- Layer 2 Security
  • JNCIS-ENT(JN0-343)- OSPF
  • JNCIS-ENT(JN0-343)- IS-IS
  • JNCIS-ENT(JN0-343)- BGP
  • JNCIS-ENT(JN0-343)- Protocol Independent Routing; Tunnels
  • JNCIS-ENT(JN0-343)- High Availability

So have you been longing for more training in some of these areas??? IS-IS perhaps??? These courses are really going to blow you away in their level of coverage, and overall approach.

The First Course – Layer 2:

What minimum topics list will we cover in the exciting first course on Layer 2 technologies? Check it out:

  • Identify the concepts, operation, and functionality of Layer 2 switching
  • Identify the concepts, benefits, and functionality of VLANs
  • Demonstrate knowledge of how to configure, monitor and troubleshoot Layer 2 switching and VLANs
  • Identify the concepts, benefits, operation, and functionality of the Spanning Tree Protocol
  • Demonstrate knowledge of how to configure and monitor STP and RSTP

Don’t miss this incredible opportunity to boost your knowledge of core routing and switching topics!
Microsoft Press

Learning Product Review – Cisco Learning Labs for CCNP SWITCH v2.0

I was very excited to check out the Cisco Learning Labs for CCNP SWITCH v2.0 50-hour 180-day Labs. So many students are looking for SWITCH practice since GNS3 falls short here (in my opinion) and sometimes we do not have access to the horsepower required for Cisco VIRL. Or more accurately for me, I do not feel like making my VPN connection to my central VIRL box. 🙂

Lab Product Overview:

So here is the premise – for a price tag of $85 (at this time), we get 50 hours of access (over a maximum of 180 days) to the routers and switches we need to practice for SWITCH. We also get plenty of lab exercises to follow if we are not feeling creative enough to create our own. If my math is correct – this is $1.70 per hour of lab time. That is a screaming deal. The rack rental vendor I sometimes use is $10 for 3 hours. I thought that was a deal before this came along!

Purchasing the Labs:

The purchase was painless, although my password was not synced in the lab site to the site. I took care of this with a simple password reset procedure that was available. To purchase, just use this link – Cisco Learning Labs for CCNP SWITCH v2.0 50-hour 180-day Labs. For some reason the price shows as $100 from that link, but I believe you get a discount once you log in.

The Lab Experience:

Logging in provides a friendly interface that shows the labs and provides information on how much time I have remaining.

Lab Interface

NOTE: The picture above is not showing all of the many labs that are available…that was cut off.

Choosing Start Lab brings you to a topology map complete with clickable router and switch images. Click on one of these and a terminal window appears ready for you to follow the lab steps that are also provided.

The Lab

I was thrilled to see that I could not tell this equipment from live gear. In fact, I had no idea what I was dealing with from a technology standpoint. The devices sure seemed “real”, which is exactly what you want in your practice lab. Out of intense curiosity I ran a show version to learn that this is indeed powered by virtual images (Cisco IOS on UNIX for the device I checked).


I would be sure to check the requirements for these labs, of course. I was on a Mac and tested them in Safari and Google Chrome. They worked flawlessly in each browser. Just be sure you are on equipment they support and obviously your Internet connection is stable. Also, I would recommend you have a printer handy. Even though your instructions pop out, I am guessing that freshers would want to print out instructions to go over them very carefully as they sit at their command line windows.

Enjoy this incredible learning opportunity at an incredible price tag! Bravo Cisco!