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OSPF Questions

March 16th, 2020 Go to comments

Question 1

Question 2

Question 3

Explanation

The Broadcast network type is the default for an OSPF enabled ethernet interface (while Point-to-Point is the default OSPF network type for Serial interface with HDLC and PPP encapsulation).

Reference: https://www.oreilly.com/library/view/cisco-ios-cookbook/0596527225/ch08s15.html

Question 4

Question 5

Question 6

Explanation

Router2 does not have an entry for the subnet 10.10.13.128/25. It only has an entry for 10.10.13.0/25, which ranges from 10.10.13.0 to 10.10.13.127.

Question 7

Explanation

The default OSPF network type for HDLC and PPP on Serial link is point-to-point (while the default OSPF network type for Ethernet link is Broadcast).

Question 8

Explanation

OSPF uses the following criteria to select the router ID:
1. Manual configuration of the router ID (via the “router-id x.x.x.x” command under OSPF router configuration mode).
2. Highest IP address on a loopback interface.
3. Highest IP address on a non-loopback and active (no shutdown) interface.

Question 9

Explanation

From the output we can see there are Designated Router & Backup Designated Router for this OSPF domain so this is a broadcast network (point-to-point and point-to-multipoint networks do not elect DR & BDR) -> Answer B is not correct.

By default, the timers on a broadcast network (Ethernet, point-to-point and point-to-multipoint) are 10 seconds hello and 40 seconds dead (therefore answer C is correct). The timers on a non-broadcast network are 30 seconds hello 120 seconds dead.

From the line “Neighbor Count is 3”, we learn there are four OSPF routers in this OSPF domain -> Answer D is not correct.

Question 10

Explanation

With the same route (prefix), the router will choose the routing protocol with lowest Administrative Distance (AD) to install into the routing table. The AD of Internal EIGRP (90) is lowest so it would be chosen. The table below lists the ADs of popular routing protocols.

EIGRP_Administrative Distances_popular_routing_protocols.jpg

Note: The AD of IS-IS is 115. The “EIGRP” in the table above is “Internal EIGRP”. The AD of “External EIGRP” is 170. An EIGRP external route is a route that was redistributed into EIGRP.

Question 11

Explanation

The default-information originate command advertises a default route into a normal area, provided the advertising router already has a default route. But in the routing table of R1 we don’t see such a default route. Therefore we have to configure one.

Question 12

Explanation

The AD of eBGP (20) is smaller than that of OSPF (110) so the route to 10.10.13.0/25 will be updated as being learned from the new BGP path.

Comments (18) Comments
  1. Anonymous
    April 19th, 2020

    q6, there’s different answer between the link and the explanation.

  2. marie
    April 25th, 2020

    @9tut, on question 6 the answer is actually D not C

  3. 9tut
    April 25th, 2020

    @marie: There are no entry to match subnet 10.10.13.128/25 so the packets are discarded so the correct answer is C.

  4. tutut
    May 2nd, 2020

    for q10, why ans not D?

  5. Saul
    May 4th, 2020

    @marie, in Q6 the answer is C because 10.10.13.128/25 is a broadcast address, Somebody told me OSPF can route broadcast address (I do not know if that is true), but for CCNA level it is out of scope.

    @tutut, Q10, the answer is D beacuse EIGRP has the lowest metric for that protocols.

  6. Saul
    May 4th, 2020

    Sorry 10.10.13.128/25 is network address not broadcast.

  7. Hihi
    May 6th, 2020

    q6 differen betwen quiz and explanation.

  8. anonymous
    May 6th, 2020

    Questıon 10, which answer is correct? two different answers in the quız and in the descriptions why?

  9. 9tut
    May 6th, 2020

    @Hihi: Thanks for your detection, we have just updated the quiz!
    @anonymous: The correct answer for Q.10 is “Internal EIGRP”.

  10. SA
    May 10th, 2020

    For question 8 what should be the right answer? C or D?

  11. pj
    May 12th, 2020

    For question 12- How do I know any information for inter gi0/1?

  12. Bong
    May 14th, 2020

    What quiz, could you please give me the link of the quiz you guys are talking about.. Please

  13. C@rlito
    May 14th, 2020

    Where i can download a complete free training materials for CCNA 200-301?

  14. Anwar
    May 18th, 2020

    Question-6
    9on question 6 the answer is actually D not C
    Can you please update the Answer there.. as well . which still showing C

  15. Pawel
    May 20th, 2020

    @Anwar

    I think it is correct because
    10.10.13.128/25

    /25 means you have: ||||||||.||||||||.||||||||.|0000000

    Increment is 128 so you will have ranges:

    10.10.13.0 -> 10.10.13.127
    10.10.13.128

    Please correct me if I’am wrong in this logic.

    Thanks!

  16. Tchalieu
    May 27th, 2020

    Q12 i m not understand the answer where did you get the ip address G0/1?

  17. Manuel
    May 28th, 2020

    Q12 could be D because G0/0 is directly conected?

  18. dotan
    June 14th, 2020

    For all those who think there is a problem in question 6
    /25
    explanation:
    127 is a broadcast address, and 128 is a network address

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