OSPF LSA Types Explained

This topic is to discuss the following lesson:

Great job,your example are very smooth to learn .

very concise exlanation! :slight_smile:

I have to tell you that I have seen different videos and took CCNP Training and never understood completely the Area Types but you explain it so easy that I understand now.

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In the above topology, when I redistribute connected on R2 and R3, R1 sees only one LSA type 4. It’s for R2 showing how to get to R3. Why don’t we also see an LSA type 4 for R2’s redistributed routes? Does a directly connected router not generate an LSA type 4 for its redistributed routes? Whew!


In your explanation about LSA type 5, you wrote :
“Here you can see the type 5 external LSA in the LSDB. Keep in mind that router R2 and R3 both are in area 0.”

But, in the design, we can see that there are in area 1 ?


Hi Luca,

Thanks for pointing that out, it’s an typo that I just fixed.


Hi Bruce,

LSA Type 4 is used so routers in other areas can find the ASBR, since R1 and R2 are in the same area (R1 already knows the router ID of R2 btw) there is no need to install LSA type 4 in the LSDB of R1.


Hi Rene
I am new at this field, I am glad I found this website.
Your explanations are just great. Thank you very much.

Hi Mohammed,

Glad to hear you like it!


There is no router Mary(Understood it is R3) Seen … just a small typo…

Thanks for letting me know, just fixed it.

I was at the same boat man. Now is crystal clear.

Well Done Again man, looks like you are a Messi in Network. Keep up the amazing work and we will be here to support. (Y)

Thanks Mauro :slight_smile:

Dear Rene,

When I learned about OSPF, I still confused about the difference of E1 and E2 Type of External LSA. Could you explain about this too?

Hi August,

When you use E2, the cost of the redistributed route always remain the same (cost 20). When you use E1, the cost will increment just like any other OSPF route.


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I was confused for a while where the router was coming from, maybe I missed it somewhere. I finally figured it was a loopback on r2 the border router, after scrolling up and down a few times. If that is correct maybe you could add it to your diagram. This whole thing was nicely done though.

Hi Cristopher,

Good idea, I just updated the diagrams so R2 has a loopback interface. Thanks for letting me know!



Thanks so much, that was way fast… Cisco fast!