OSPF

Question 1

When OSPF is forming an adjacency, in which state, the actual exchange of information in the link?

A. INIT
B. loading
C. exstart
D. exchange

Answer: B

Loading: In this state, the actual exchange of link state information occurs. Based on the information provided by the DBDs, routers send link-state request packets. The neighbor then provides the requested link-state information in link-state update packets. During the adjacency, if a router receives an outdated or missing LSA, it requests that LSA by sending a link-state request packet. All link-state update packets are acknowledged.

Question 2

OSPF chooses routes in which order, regardless of route’s adminstrative distance and metric?

A. Interarea
B. Intra-area
C. NSSA type1
D. NSSA type 2
E. External type1
F. External type2

Answer:

Order: B A E F C D (Intra-Area (O); Inter-Area (O IA); External Type 1 (E1); External Type 2 (E2); NSSA Type 1 (N1); NSSA Type 2 (N2))

Question 3

Refer to the exhibit. A network engineer executes the show ipv6 ospf database command and is presented with the output that is shown. Which flooding scope is referenced in the link-state type?

A. link-local
B. area
C. AS (OSPF domain)
D. reserved

Answer: B

Question 4

area 1 range 10.1.0.0 255.255.0.0
summary address 10.1.0.0 255.255.0000

What is the effect of those two commands?

A. area 1 range: command applied to summarize internal OSPF routes (ABR)
B. area 1 range: command applied to summarize external OSPF routes (ASBR)
C. Summary address: command applied to summarize external OSPF routes (ASBR)
D. Summary address: command applied to summarize internal OSPF routes (ABR)

Answer: A C

Question 5

Which LSAs present in OSPF stub area?

A. LSA 1,2,3,4,5
B. LSA 1,2,5
C. LSA 1,2,3
D. LSA 3,5

Answer: C

+ Standard areas can contain LSAs of type 1, 2, 3, 4, and 5, and may contain an ASBR. The backbone is considered a standard area.
+ Stub areas can contain type 1, 2, and 3 LSAs. A default route is substituted for external routes.
+ Totally stubby areas can only contain type 1 and 2 LSAs, and a single type 3 LSA. The type 3 LSA describes a default route, substituted for all external and inter-area routes.
+ Not-so-stubby areas implement stub or totally stubby functionality yet contain an ASBR. Type 7 LSAs generated by the ASBR are converted to type 5 by ABRs to be flooded to the rest of the OSPF domain.

Question 6

Which OSPF area has type 7 LSA?

A. NSSA
B. Total stubby
C. Stubby area
D. Normal area

Answer: A

NSSA External LSA (Type 7) – Generated by an ASBR inside a Not So Stubby Area (NSSA) to describe routes redistributed into the NSSA. LSA 7 is translated into LSA 5 as it leaves the NSSA. These routes appear as N1 or N2 in the routing table inside the NSSA. Much like LSA 5, N2 is a static cost while N1 is a cumulative cost that includes the cost upto the ASBR.

Question 7

Which type of address does OSPFv3 use to form neighbor adjacencies and to send LSAs?

A. unicast IPv6 addresses
B. link-local addresses
C. multicast address FF02::5
D. unicast IPv4 addresses

Answer: C

OSPFv3 uses the well-known IPv6 multicast addresses, FF02::5 to communicate with neighbors. The FF02::5 multicast address is known as the AllSPFRouters address. All OSPFv3 routers must join this multicast group and listen to packets for this multicast group. The OSPFv3 Hello packets are sent to this address.

Note: All other routers (non DR and non BDR) establish adjacency with the DR and the BDR and use the IPv6 multicast address FF02::6 (known as AllDRouters address) to send LSA updates to the DR and BDR.

The answer “link-local addresses” is also correct too. The reason is OSPFv3 routers use link-local address (FE80::/10) on its interfaces (as the source address) to send Hello packets to FF02::5 (as the destination address). So in fact this question is not clear and there are two correct answers here.

Note: The two IPv6 multicast addresses FF02::5 and FF02::6 have link-local scope.

Question 8

Which LSA type can exist only in an OSPF NSSA area?

A. type 7 LSA
B. type 1 LSA
C. type 5 LSA
D. type 3 LSA

Answer: A

NSSA External LSA (Type 7) – Generated by an ASBR inside a Not So Stubby Area (NSSA) to describe routes redistributed into the NSSA. LSA 7 is translated into LSA 5 as it leaves the NSSA. These routes appear as N1 or N2 in the routing table inside the NSSA. Much like LSA 5, N2 is a static cost while N1 is a cumulative cost that includes the cost upto the ASBR.

OSPF_LSAs_Types_7.jpg

Question 9

A route map was configured and it was distributing OSPF external routes.

A. Distributing E1 only
B. Distributing E1 and E2 using prefix list
C. Distributing E1 and E2 using access list
D. Distributing E2 routes

Answer: B

Question 10

You have a router has some interface configured with 10Gbps interface and 1Gbps interface. Which command you use to optimize higher bandwidth?

A. auto-cost reference-bandwidth 10000
B. cost 10000
C. reference-bandwidth 10000
D. auto-cost 10000

Answer: A