Question 1.
Your addressing plan has assigned the entire range 192.168.0.0/18 to OSPF area 0.0.0.1. What are the correct area...range statement(s) to summarize this block?

area 0.0.0.1 range 192.168.0.1 255.255.192.0

area 0.0.0.1 range 192.168.0.0 255.255.192.0

area 0.0.0.1 range 192.168.2.0 255.255.254.0
area 0.0.0.1 range 192.168.4.0 255.255.248.0

area 0.0.0.1 range 192.168.2.0 0.0.31.255

Answer

Question 2.
What features are not supported by an OSPF totally stubby area?
(Choose 2)

a) multiple ABRs
b) virtual links
c) lowest-cost end-to-end routes
d) default routes

Answer

Question 3.
In OSPF, what are the main factors that limit, in practice, the number of nonzero areas you can connect to an ABR?
(Choose 2)

a) Stability of each area
b) CPU power of the ABR
c) Number of routers in each area
d) Degree to which routes are summarized into area 0.0.0.0

Answer

Answers

Question 1.
Your addressing plan has assigned the entire range 192.168.0.0/18 to OSPF area 0.0.0.1. What are the correct area...range statement(s) to summarize this block?

area 0.0.0.1 range 192.168.0.1 255.255.192.0

area 0.0.0.1 range 192.168.0.0 255.255.192.0

area 0.0.0.1 range 192.168.2.0 255.255.254.0
area 0.0.0.1 range 192.168.4.0 255.255.248.0

area 0.0.0.1 range 192.168.2.0 0.0.31.255

area 0.0.0.1 range 192.168.0.0 255.255.192.0

Explanation
Choice B is correct because you want to summarize a contiguous range.

Choice A is wrong because it starts on an "odd" bit boundary; perhaps you were thinking subnet 0 restrictions applied. Choice C only summarizes a few of the address blocks in the area. Choice D is wrong because area...range statements, as opposed to network statements, use subnet, not network, masks.
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Question 2.
What features are not supported by an OSPF totally stubby area?
(Choose 2)

a) multiple ABRs
b) virtual links
c) lowest-cost end-to-end routes
d) default routes

Answer
b) virtual links
c) lowest-cost end-to-end routes

Explanation
It is a common misconception that totally stubby areas do not support multiple ABRs. The restriction is that routers inside the area will only consider the intra-area cost to reach the closest ABR. In a totally stubby area, routers are not aware of costs outside the area.

Virtual links cannot traverse any kind of stubby area.
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Question 3.
In OSPF, what are the main factors that limit, in practice, the number of nonzero areas you can connect to an ABR?
(Choose 2)

a) Stability of each area
b) CPU power of the ABR
c) Number of routers in each area
d) Degree to which routes are summarized into area 0.0.0.0

Answer
a) Stability of each area
b) CPU power of the ABR

Explanation
The danger of having too many areas connected to the same ABR is that multiple areas might simultaneously need to run a CPU-intensive Dijkstra calculation. The more areas, the more likely this is. The more unstable a given area is, the more likely that it will need frequent recomputations.

The computational workload associated with the number of routers is based on the logarithm of the number of routers, where the load from intra-area links increases by the square of the number of links.

Summarization decreases the workload in area 0.0.0.0, but doesn't decrease the load in the nonzero areas.
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