OSPF – 3

Question 1

Which are new LSA types in OSPF for IPv6 (OSPFv3)? (Choose two)

A. LSA Type 8
B. LSA Type 9
C. LSA Type 10
D. LSA Type 12

Answer: A B

LSAs Type 8 (Link LSA) have link-local flooding scope.  A router originates a separate link-LSA for each attached link that supports two or more (including the originating router itself) routers.  Link-LSAs should not be originated for virtual links.

Link-LSAs have three purposes:
1.  They provide the router’s link-local address to all other routers attached to the link.
2.  They inform other routers attached to the link of a list of IPv6 prefixes to associate with the link.
3.  They allow the router to advertise a collection of Options bits in the network-LSA originated by the Designated Router on a broadcast or NBMA link.

LSAs Type 9 (Intra-Area Prefix LSA) have area flooding scope. An intra-area-prefix-LSA has one of two functions:
1.  It either associates a list of IPv6 address prefixes with a transit network link by referencing a network-LSA…
2.  Or associates a list of IPv6 address prefixes with a router by referencing a router-LSA.  A stub link’s prefixes are associated with its attached router.

LSA Type 9 is breaking free of LSA Type 1 and LSA Type 2 as they were used in IPv4 OSPF to advertise the prefixes inside the areas, giving us a change in the way the OSPF SPF algorithm is ran.

Question 2

If routers in a single area are configured with the same priority value, what value does a router use for the OSPF Router ID in the absence of a loopback interface?

A. The lowest IP address of any physical interface
B. The highest IP address of any physical interface
C. The lowest IP address of any logical interface
D. The highest IP address of any logical interface

Answer: B

Question 3

You get a call from a network administrator who tells you that he typed the following into his router:

Router(config)#router ospf 1
Router(config-router)#network 10.0.0.0 255.0.0.0 area 0

He tells you he still can’t see any routes in the routing table. What configuration error did the administrator make?

A. The wildcard mask is incorrect
B. The OSPF area is wrong
C. The OSPF process ID is incorrect
D. The AS configuration is wrong

Answer: A

The wildcard mask should be 0.0.0.255 instead of the subnet mask 255.0.0.0.

Question 4

Which type of OSPF router can be aggregated? (Choose two)

A. the ABR
B. the ASBR
C. Backbone Router
D. Intra Router

Answer: A B

Route aggregation can be performed on the border routers to reduce the LSAs advertised to other areas. Route aggregation can also minimize the influences caused by the topology changes.

Question 5

Which two OSPF network types can operate without a DR/BDR relationship? (Choose two)

A. Point-to-multipoint
B. Point-to-point
C. nonbroadcast
D. nonbroadcast multi-access
E. broadcast

Answer: A B

Question 6

If you want to migrate an IS-IS network to another routing protocol. Which routing protocols should you choose? (Choose two)

A. UDP
B. internal BGP
C. TCP/IP
D. EIGRP
E. OSPF
F. RIP

Answer: (maybe) D E

IS-IS is an interior gateway protocol (IGP), same as EIGRP and OSPF so maybe they are the best answers. Although RIP is not a wrong choice but it is not widely used because of many limitations (only 15 hops, long convergence time…).

Question 7

If you configure one router in your network with the auto-cost reference-bandwidth 100 command, which effect on the data path is true?

A. The data path remains the same for all links
B. The data path changes for 10Mbps links only
C. The data path changes for all links
D. The data path changes for 10Gbps links only

Answer: C

This command affects all the OSPF costs on the local router as all links are recalculated with formula: cost = reference-bandwidth (in Mbps) / interface bandwidth 

Note: The default reference bandwidth for OSPF is 10^8 bps or 100Mpbs so the “auto-cost reference-bandwidth 100” is in fact the default value so answer A may be  a correct answer.

Question 8

Refer to the exhibit. In the network diagram, Area 1 is defined as a stub area. Because redistribution is not allowed in the stub area, EIGRP routes cannot be propagated into the OSPF domain. How does defining area 1 as a not-so-stubby area (NSSA) make it possible to inject EIGRP routes into the OSPF NSSA domain?

Redistribute_EIGRP_OSPF_NSSA.jpg

A. by creating type 5 LSAs
B. by creating type 7 LSAs
C. by creating a link between the EIGRP domain and the RIP domain, and redistributing EIGRP into RIP
D. by manually changing the routing metric of EIGRP so that it matches the routing metric of OSPF

Answer: B

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

Which two routers can do OSPF route summarization? (Choose two)

A. ABR
B. ASBR
C. Summary router
D. Internal router
E. Backbone router

Answer: A B