nerdexam
Cisco

352-001 · Question #202

Refer to the exhibit. In this network, R1 is redistributing 10.1.5.0/24 into Area 1. Which LSA containing 10.1.5.0/24 will R6 have in its database?

The correct answer is D. R6 will not have any LSAs containing 10.1.5.0/24.. In OSPF, a totally stubby area blocks Type 3, 4, and 5 LSAs from entering, so a router residing in such an area will have no LSA for an externally redistributed prefix.

Layer 3 Control Plane

Question

Refer to the exhibit. In this network, R1 is redistributing 10.1.5.0/24 into Area 1. Which LSA containing 10.1.5.0/24 will R6 have in its database?

Exhibit

352-001 question #202 exhibit

Options

  • AR6 will have an NSSA external (type 7) LSA in its local database for 10.1.5.0/24.
  • BR6 will have an external (type 5) LSA for 10.1.5.0/24 in its local database.
  • CR6 will have a border router (type 4) LSA in its local database for 10.1.5.0/24.
  • DR6 will not have any LSAs containing 10.1.5.0/24.

How the community answered

(42 responses)
  • A
    5% (2)
  • B
    21% (9)
  • C
    12% (5)
  • D
    62% (26)

Why each option

In OSPF, a totally stubby area blocks Type 3, 4, and 5 LSAs from entering, so a router residing in such an area will have no LSA for an externally redistributed prefix.

AR6 will have an NSSA external (type 7) LSA in its local database for 10.1.5.0/24.

Type 7 NSSA external LSAs exist only within the NSSA area where redistribution occurred - they are not present in R6's totally stubby area.

BR6 will have an external (type 5) LSA for 10.1.5.0/24 in its local database.

Type 5 external LSAs are explicitly blocked by the ABR from entering totally stubby areas, so R6 will never receive one for this redistributed route.

CR6 will have a border router (type 4) LSA in its local database for 10.1.5.0/24.

A Type 4 LSA describes only the location of an ASBR and does not carry prefix information - it is also blocked from entering totally stubby areas.

DR6 will not have any LSAs containing 10.1.5.0/24.Correct

Based on the exhibit topology, R6 resides in a totally stubby area, which filters all Type 3 inter-area summary LSAs (except the default route), and all Type 4 and Type 5 external LSAs at the ABR. The redistributed 10.1.5.0/24 travels as a Type 5 LSA through the backbone but is explicitly blocked from flooding into R6's totally stubby area, leaving R6 with no LSA for that prefix.

Concept tested: OSPF LSA types blocked in totally stubby areas

Source: https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/5003-ospf-lsa.html

Topics

#OSPF LSA types#NSSA area#route redistribution#flooding domain

Community Discussion

No community discussion yet for this question.

Sign up to join the discussion
Full 352-001 Practice