Totally confused about stub area example and theory.

Roguetadhg · March 2012

Im using OCG, 2nd Edition:

Page 240's Figure 7-8:

[B]Area 34:[/B]
[R3] <-------- [R1]
[R4] <---/

[R3] <----\
[R4] <-------- [R2]

ABRs (R1, R2) area advertising their default route into Area 34. Both ABRs advertise to both Area 34 routers (R3, R4).
ABRs are connected to Area 0. See below for Area 0 information.

[B]Area 0:[/B]
External Routes: 
11.11.0.0/16
11.12.0.0/16
11.13.0.0/16

Data Center:
10.16.11.0/24
10.16.12.0/24
10.16.13.0/24

I've gone over the example 5 times in my head, after reading the next small section on Configuration.

First the example that I've been focused on:

"For example, consider the diagram in Figure 7-8 with area 34 as simply a stub area. ...[Explains it filters the External routes]... Finally, because the area is not a totally stubby area, the ABRs do create and flood Type 3 LSAs for interarea routes as usual, so they flood LSAs for the 10.16.11.0/24, 10.16.12.0/24, and 10.16.13.0/24 subnets listed in the figure."

However, in the configuration section, afterwards - on the same page (241):

"Figure 7-9 shows a more detailed view of Area 34 from Figure 7-8, so by making area 34 a stub area, ABRs R1 and R2 will not flood Type 5 LSAs into area 34 - other than the Type 3 LSA for the default routes."

The configuration shows that "Area 34 stub" has been configured. Making the area a "Stub" area. Not a "Totally Stubby" area - which as I understand "Totally Stubby/Totally NSSA" filters all Type 3 LSAs, besides the default route.

With the backdrop set, this is my confusion:
1) If Area 34 is considered a "Stub" U]Not[/U] [I]Totally Stubby[/I area, why would the configuration example say: "Other than the Type 3 LSA for the default routes."
a) Should it be advertising the Type 3 LSAs for the Data Center subnets [10.13.11.0/24...] as well?

As for Figure 7-9: I]Shows the physical connections/Ip addresses. As well as R3 and R4 are connected together by a LAN[/I

Thread name pun intended.

I am looking for a solution using the internet, but the sources I've found all explain that Type 3 wouldn't be filtered.
One source: http://users.lmi.net/canepa/subdir/ospf_fundamentals.html

NetworkVeteran · March 2012

Roguetadhg wrote:

by making area 34 a stub area, ABRs R1 and R2 will not flood Type 5 LSAs into area 34 - other than the Type 3 LSA for the default routes."
a) If Area 34 is considered a "Stub" U]Not[/U] [I]Totally Stubby[/I area, why would the configuration example say: "Other than the Type 3 LSA for the default routes."
b) Should it be advertising the Type 3 LSAs for the Data Center subnets [10.13.11.0/24...] as well?

If area 34 is a stub area--,
1. ABRs will not flood type-5 LSAs into area 34, period.
2. ABRs will flood type-3 LSAs.
3. ABRs will generate and flood a type-3 LSA for the default route.

If you add the no-summary keyword to the area 34 ABRs to make the area totally stubby, everything stays the same except for #2--ABRs will stop flooding type-3 (summary) LSAs.

PS - I do not own that book.

mattau · March 2012

what NetworkVeteran said, that is definitely a typo in the book

MrBrian · March 2012

For this book, going through the errata is a must!!

I went through this book going for my ROUTE exam and it's absolutely chocked full of errors.

MrXpert · March 2012

MrBrian wrote: »

For this book, going through the errata is a must!! I went through this book going for my ROUTE exam and it's absolutely chocked full of errors.

well at least their consistent if nothing else.

Roguetadhg · March 2012

i tried to thoroughly explain why I was confused and give enough information to get help even if no one had the book.

Thank you, everyone.

Back at it...

Totally confused about stub area example and theory.

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