Home > ICND2 – OSPF Questions 5

ICND2 – OSPF Questions 5

October 13th, 2017 in ICND2 200-105 Go to comments

Question 1

Explanation

All areas in an OSPF autonomous system must be physically connected to the backbone area (Area 0). In some cases, where this is not possible, you can use a virtual link to connect to the backbone through a non-backbone area. With the use of a single OSPF are (for example all the routers are put in area 0), we will not need virtual links any more -> Answer B is correct.

If we only use one OSPF area then only LSA 1 & 2 are generated (no need for other LSAs like type 3, 4, 5, 7…) -> Answer C is correct.

Question 2

Question 3

Explanation

The well-known formula to calculate OSPF cost is

Cost = 108 / Bandwidth

so B is the correct answer.

Question 4

Explanation

The default number of equal-cost paths that can be placed into the routing of a Cisco OSPF router is 4. We can change this default value by using “maximum-paths” command:

Router(config-router)#maximum-paths 2

Note: Cisco routers support up to 16 equal-cost paths

Question 5

Question 6

Explanation

The Administrative Distances (AD) of popular routing protocols are listed below:

Administrative Distances_popular_routing_protocols.jpg

Question 7

Question 8

Explanation

The question states that the link to ISP should not participate in OSPF -> answers A, B are not correct.

In answer D, the “network 10.10.2.32 0.0.0.31 area 0” does not cover the IP address of S0/0.103 (10.10.2.21) -> D is not correct.

The default-information originate command advertises a default route to other routers, telling something like “please send me your unknown traffic”. So in this case, besides a full routing table, other routers will also receive a default route from Core router.
But please notice that Core router needs to have a default route in its routing table. That is why the command “ip route 0.0.0.0 0.0.0.0 10.10.2.14” is added to Core router. By adding the “always” (after “default-information originate” command) the default route will be advertised even if there is no default route in the routing table of router Core.

Question 9

Explanation

The default-information originate command advertises a default route to other routers, telling something like “please send me your unknown traffic”. So in this case, besides a full routing table, R2 will also receive a default route from R1 -> B is correct.

Note: But in this question, the static route should be “ip route 0.0.0.0 0.0.0.0 serial0/1″ (not serial0/0), that may cause a routing loop.

Question 10

Explanation

A loopback interface never comes down even if the link is broken so it provides stability for the OSPF process (for example we use that loopback interface as the router-id) -> B is correct.

The router-ID is chosen in the order below:

+ The highest IP address assigned to a loopback (logical) interface.
+ If a loopback interface is not defined, the highest IP address of all active router’s physical interfaces will be chosen.

-> The loopback interface will be chosen as the router ID of RouterB -> C is correct.

Question 11

Explanation

First, notice that the more-specific routes will always be favored over less-specific routes regardless of the administrative distance set for a protocol. In this case, because we use OSPF for three networks (172.16.100.0 0.0.0.3, 172.16.100.64 0.0.0.63, 172.16.100.128 0.0.0.31) so the packets destined for these networks will not be affected by the default route.

The default route configured on R1 “ip route 0.0.0.0 0.0.0.0 serial0/0″ will send any packet whose destination network is not referenced in the routing table of router R1 to R2, it doesn’t drop anything so answers A, B and C are not correct. D is not correct too because these routes are declared in R1 and the question says that “OSPF has been correctly configured on router R2″, so network directly connected to router R2 can communicate with those three subnetworks.

As said above, the default route configured on R1 will send any packet destined for a network that is not referenced in its routing table to R2; R2 in turn sends it to R1 because it is the only way and a routing loop will occur.

Comments (3) Comments
  1. CCNA Test Taker
    November 1st, 2017

    For question 1. I don’t understand why C – virtual links?

  2. 9tut
    November 2nd, 2017

    @CCNA Test Taker: We have just added explanation to Q.1. Please read it again.

  3. CCNA Test Taker
    November 2nd, 2017

    Thank you 9tut!!!