NSSA vs Stub !?

[mohammed hashim]

hi,

with this table, 

so Stub area does not install anything above LSA3, instead it uses default route. essentially there is only LSA4 and LSA5 needed, this is because LSA7 is made specially for NSSA areas.

in contrast, NSSA share some of this operation with Stub area except that for external route, instead of injecting it as LSA5, use LSA7 !!

so now NSSA does also the same as Normal area, means it accept external routes injection, and it use LSAs 1, 2 and 3

Q1\ what is the different here in the operation between Normal area NSSA area !?

Q2\ if NSSA only provide LSA7 injection, why this is not made as an option on Stub area instead of developing new Area type?

thanks,

[Joseph W. Doherty]

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Posting

Q1: other OSPF area LSAs are blocked.

Q2: not only, but more.  It supports injection of externals.  This feature is what's added to a stub to make it NSSA.

[Richard Burts · Accepted solution]

Q1 In a normal area, for example perhaps area 1 is a normal area. In that normal area it could receive an LSA type 5 for an external route learned from area 2 and could also have an ASBR in area 1 redistributing some protocol and generating external routes within the area. If area 3 were NSSA it would not receive the external route generated in area 2. It would only have the type 7 generated by the ASBR in its own area. So the main difference between a normal area and an NSSA area is that the normal area can receive external routes generated in some other area while the NSSA does not receive external from other areas.

Q2 NSSA is an option in the stub area and is not a new area type.

HTH

Rick

[mohammed hashim]

thanks for clarification

[Richard Burts]

You are welcome. Thank you for using the rating system to mark this question as answered. This will help other readers in the forum to identify discussions that have helpful information. These forums are a good place to learn about networking and to find solutions for problems. I hope to see you continue to be active in the forums.

HTH

Rick

[mohammed hashim]

Hi Richard, 

I have always seen you and Joseph and other experts here helping us to be experts :)

"one day hopefully"

I am really thankful for all your help,,,

[Richard Burts]

Thank you for the kind words. At one point I was also a beginner who was learning about networking. I was grateful to have people who showed me the way and shared what they knew. So I am glad to now be able to show other people the way and to share what I know. As you learn more you will also be able to help others and I hope that you will.

HTH

Rick