Objections to the OSPF quiz

CriscoSystems · ‎04-10-2009

Well I just took the "Do I know this already" quiz on multi-area OSPF in my BSCI textbook. I got most of the questions right, some I got rightfully wrong, but others I got wrongfully wrong.

Here are my objections:

Q3: Which of the following statements explain why this feature (use of areas) is such an important enhancement on earlier routing protocols?

The two "correct" answers include "B" (area summarization reduces routing table size & spf calculations), and "D" which reads: "The use of multiple areas allows for the use of prioritization."

Prioritization? That's an interface/DR election thing, not an areas thing. How could that be listed as a correct answer?

Q8: Which of the following conditions must be met before any LSAs can be flooded out of all the interfaces?

"A" "B" and "C" are all correct. A = Exchange or Full state, B = interface not connected to totally stubby area, C = LSA not received on same interface.

A and C I'm cool with. But isn't it messy to say "interface must not be connected to a totally stubby area" when the question didn't specify that we were dealing with LSA's that aren't Type 1 or 2; it also didn't specify that we were talking about an ABR/ASBR. Type 1 and Type 2 LSA's still get flooded throughout the area they originate in, even if it's a totally stubby area, right? So an internal router (in exchange or full state) in a total stub area gets a Type 1 or 2 LSA, it will flood those LSA's out all its other interfaces, won't it? If so, then that question was poorly put together. Nice going.

Q9: Which of the following affect how the routing table is created?

Correct answers are "A" ("Whether there are multiple areas in the domain"), "C" ("The type of area where the router is"), and "D" ("Whether there are communications outside the AS.")

I say that "A" doesn't affect the ROUTING table, but rather the TOPOLOGY table. Area-ness doesn't necessarily impact the cost of the routes; the RT just has to put an "IA" on the screen. Interarea routes have the same AD, don't they? And the same goes for "C" - the type of area determines which LSA's are allowed in, that in turn affects the TOPOLOGY table, not the routing table. The RT is built from the topology table, and by the time the topology table is built, we're done looking at area types.

"D". Yeah, I'll grant them that (E1 and E2 routes and all). Still the question is enragingly vague.

lamav · ‎04-10-2009

Seth:

Take it easy, dude...really. You sound really angry.

It's Friday night, my friend. Put the book down, get that razor away from your wrist, and go have a beer or two. Trust me, it'll all seem so unimportant tomorrow. :-)

Good night

Victor

CriscoSystems · ‎04-10-2009

Dude.

I want to PASS the BSCI exam.

lamav · ‎04-11-2009

Seth:

You will pass. Dont worry. The fact that you dont agree with the book's answers only means that you are thinking critically. And that is precisely why you'll pass.

Victor

paolo bevilacqua · ‎04-11-2009

Fact: in most Cisco tests (including the all-important CCIE), there is a number of questions that are either vague, ill-formulated or plain wrong.

Personally I estimate thse to be around 5% of the total.

Fact: Cisco uses "beta" periods when introducing new tests, sometime for a discounted price. As we all know, something introduced as "beta" is implicitly recognized to have bugs.

Fact: a candidate that fails a "wrong" question, can possibly fail the whole test as a consequence, thing on which he/she has NO remedy, as no system is in place for cisco to receive feedback or complains on the test content or results.

Fact: the presence of such question that can be answered correctly only by memorizing the answer rather than using logic and knowledge, furthermore encourages the use of the well known cheat sheets.

scottmac · ‎04-11-2009

There are also some beta questions included that are not scored on many / most tests.

Marwan ALshawi · ‎04-11-2009

ok i will give you some hints that will help you :)

for The use of multiple areas allows for the use of prioritization

here the prioritization can be interpreted as

OSPF first consider any INTRA AREA route before inter area route even if the inter area route has less cost !!!

for the other question

Area-ness doesn't necessarily impact the cost of the routes; the RT just has to put an "IA" on the screen. Interarea routes have the same AD, don't they?

you can know it now from the above answer

intera area route prefered over inter area route that why IA is need it

if u have route learned from other area and from your area the one from the same area wil be chosen

for external route

remember

E1 prefered over E2 default E2

good luck

hope this will help

CriscoSystems · ‎10-20-2009

Thanks Marwan.

Is this thingy, where intra-area is preferred over lower-cost interarea routes, documented somewhere in the RFC; or in the Cisco documentation?

Giuseppe Larosa · ‎10-20-2009

Hello Stuey,

OSPF has this hierarchy of routes built-in.

as a short formula hierarchy can be expressed as:

O > O IA > O E1 > O E2

intra area routes are preferred over inter-area routes,

O E1 are preferred over O E2.

see

http://www.cisco.com/en/US/docs/internetworking/technology/handbook/OSPF.html#wp1020556

and

http://www.ietf.org/rfc/rfc2328.txt

Hope to help

Giuseppe