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

This blog is about the things I learned about computers and networking to help me to remember them as I push further my studies. I created this blog to help myself to continue my education; and if you find this blog helpful for your studies, that is great. That is one of the reasons why I made this blog, to share my interest and knowledge. Also, all the entries/posts 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 BTC: 14wVPFBWNAKmfNsgUrPpw8EytkXFLjxYoU ETH: 0x8528793dF77a57186f5B15dA6DC1eaA3c5e92c4a LTC : LMpW2rGYnYdUwvnHA4huB6TGcPEEc1JzXw
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