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OSPF Questions 3

March 23rd, 2017 in ICND2 200-105 Go to comments

Question 1


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

In answer D, the “network area 0” does not cover the IP address of S0/0.103 ( -> 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” 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 2


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 serial0/1″ (not serial0/0), that may cause a routing loop.

Question 3


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 4


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 (,, so the packets destined for these networks will not be affected by the default route.

The default route configured on R1 “ip route 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.

Question 5


The highest IP address of all loopback interfaces will be chosen -> Loopback 0 will be chosen as the router ID.

Question 6


The output of the “show ip ospf database” is shown below:


From the output above we can see LSA Type 1 (Router Link State) and LSA Type 3 (Summary Net Link State).

Question 7

Question 8


The “network″ equals to network This network has:
+ Increment: 64 (/26= 1111 1111.1111 1111.1111 1111.1100 0000)
+ Network address:
+ Broadcast address:
Therefore all interface in the range of this network will join OSPF -> B C D are correct.

Question 9

Comments (7) Comments
  1. Anonymous
    March 24th, 2017

    In Q10, why is the maximum hello is 10 and the maximum dead timer is 40? Aren’t those the default parameters?

  2. RCC
    March 27th, 2017

    Question 9 is AFU. First off its an interval not a cost. And I believe they are looking for the default settings for hello/dead, not maximum.

  3. John
    April 2nd, 2017

    sorry gys, Where are the questions

  4. Grimraven
    April 2nd, 2017

    hello-interval—Represents the length of time between the transmission of hello packets. The value can be from 1 – 65535 seconds. The default is 10 seconds.

  5. UrphinJuice
    April 6th, 2017

    Q2. If we imagine that no mistakes were done and the default interface is really s0/0. It will obviously cause the loop, and may affect the neighboring state of the routers…. Then the answer would be: Router R2 will not form a neighbor relationship with R1. Is it possible?

  6. John
    April 13th, 2017

    Guys where the questions for this answer because I can found it in the guide put in this page.

  7. Mike
    April 18th, 2017

    Q9 – the answer quoted seems to be the default OSPF timers, but depending on the type of link involved I believe max cost hello is 30s and dead time same is 120s.
    But these options do not appear in the question. There has to be a relation of 1:4 hello timer: dead timer according to everything I have seen in OSPF so the only answers which can be correct under the circumstances are A and C. But it is not absolutely correct, just the only possibly correct solution with this set of possibilities.