OSPF LSA Area Types

Figure 1

OSPF LSA  Area Types are:

Type 1 (Router): This is the local routes within an area, an intra-area routes.    On the routing table they are the ones with letter O.
E.g. Look at the Figure 1 (light green arrows), these are the routes within the area.

Type 2 (Network): This LSA is a network link route propagated by the DR.  Like Type 1, this area is intra-area as well, but the difference is this Type 2 is the one with DR/BDR routes.  Also, on the routing table they are the ones with letter O code like Type 1.
E.g. Look at the Figure 1 (light green arrows), these are the routes within the area.

Type 3 (Inter-area Summary): This LSA is the route that is being advertise by an ABR.  Meaning, routes that originates from a different area and being advertise to another area, an inter-area routes.  On the routing table their code is O IA.
E.g. Check Figure 1 (blue arrows), these routes are being advertised by ABR to the area they are connected to.

Type 4 (ASBR Summary): This is ABR advertising the ASBR location, like how to reach the ASBR, into an area routers.
E.g. Figure 1 (green broken arrows).  This is simply showing that, where the ASBR router location is, and how to reach it.

Type 5 (External Routes): These routes are the external routes that is being advertised to an area by ASBR.  Meaning, routes that is being redistributed to OSPF networks.  On the routing table these routes have either O E1 and/or O E2 codes.
E.g.  Figure 1 (purple arrows).  These routes are the routes that is being redistributed by the ASBR routers to OSPF areas.

Type 7 (NSSA):  The Type 7, Not So Stabby Area, is when the Stub area is receiving a redistributed routes within its area.
E.g. Figure 1 (Red arrows).  On the Figure 1, the Area 1 and Area 2 are both stub areas; however, Area 2 has an ASBR and getting some routes from the white cloud.  Now, the Area 2’s ASBR will create a Type 7 LSA and pass it to ABR2 (Red arrow).  Once ABR2 receives the Type 7, the ABR2 knows that it needs to advertise the Type 7 routes to the rest of the OSPF network, so what it does it will convert the Type 7 it receives and advertise it as Type 5 to the rest of OSPF network.  On Figure 1, when the Red arrows (Type 7) hits the ABR2, ABR2 advertise it as Purple arrow (Type 5).

About networkshinobi

My name is Karlo, I work as a Network Engineer. A little about myself. I started as a PC gamer back when I was in high school. PC gaming became my addiction and pushed me to learn more about computers. Slowly got my some certifications and landed an IT Tier 1 Helpdesk job. This job opened the door for me to work to push further on my certifications and going deeper into the IT world. My goal was to get my Cisco CCIE Routing and Switching, but my journey for CCIE has changed due to I always ended up working on non-Cisco network appliances. Therefore, I have to pivot and decided to jump to the dark side and go with Juniper. Hopefully, I would get my JNCIE in the near future. All the entries/post I made are based on my views, opinion and for educational purposes only. If you see some mistakes, feel free to drop some comments. I would appreciate all the helpful comments. Thanks
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