JN0-648 Exam - Question 20

Question

Click the Exhibit button. Referring to the exhibit, how is R5 able to learn the networks that exist within the NSSA?

Examice · Accepted Answer

R5 learns the networks within the NSSA from Type 3 LSAs advertised by R3. This occurs because R2, which is the Area Border Router (ABR) between the NSSA and the backbone area, creates Type 3 Summary LSAs for internal OSPF routes learned within the NSSA. These Type 3 LSAs are then flooded into the backbone area. R3, which is connected to both the backbone and the area containing R5, re-advertises these Type 3 LSAs into the area containing R5, thereby allowing R5 to learn about the networks in the NSSA.

certman20 · Answer

B is correct. The flooding scope of Type-3 LSA is a single area.

dexjov · Answer

Stub areas (in this case NSSA) influence which LSA will be allowed within that area. However, other areas will learn about OSPF internal networks of NSSA area via SLA type 3. R2 as ABR creates LSA type3 and R3 will recreate those LSAs and advertise into area where R5 is, so correct answer should be B.

silvique_ms · Answer

Think B is correct!

SB13 · Answer

Think A is correct

edu_web · Answer

A is correct!
R2 is going to create a Type 3 summary LSA and flood it into area 0. This LSA will flood into all the other areas of our OSPF network. This way all the routers in other areas will know about the prefixes from other areas.
https://networklessons.com/ospf/ospf-lsa-types-explained

monaldey · Answer

I think R2 will convert LSA7 into LSA5 and flood into area 0. And R3 will floor those route as LSA3. So B should be the correct answer.

fyoumb · Answer

Isn't A the right answer?

silvique_ms · Answer

R5 is a no-backbone area. I also think is A
https://www.juniper.net/documentation/images/g200034.png

hyena · Answer

LSA7 or LSA5 is only for redistribute routes. LSA3 will be for all internal routes.. if not cli was added for send only default , R5 will learn them as LSA3 from R2 
LSA TYPES:
    Type 1 – Router LSA: The Router LSA is generated by each router for each area it is located. In the link-state ID you will find the originating router’s ID.
    Type 2 – Network LSA: Network LSAs are generated by the DR. The link-state ID will be the interface IP address of the DR.
    Type 3 – Summary LSA: The summary LSA is created by the ABR and flooded into other areas.
    Type 4 – Summary ASBR LSA: Other routers need to know where to find the ASBR. This is why the ABR will generate a summary ASBR LSA which will include the router ID of the ASBR in the link-state ID field.
    Type 5 – External LSA: also known as autonomous system external LSA: The external LSAs are generated by the ASBR.
    Type 6 – Multicast LSA: Not supported and not used.
    Type 7 – External LSA: also known as not-so-stubby-area (NSSA) LSA: As you can see area 2 is a NSSA (not-so-stubby-area) which doesn’t allow external LSAs (type 5). To overcome this issue we are generating type 7 LSAs instead.

nushadu · Answer

ed@vMX_R2# run show ospf database

OSPF database, Area 0.0.0.1
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Router  *2.2.2.2          2.2.2.2          0x8000000f  1737  0x20 0xcb4   36
Router   4.4.4.4          4.4.4.4          0x8000000e   396  0x28 0x2067  48
Network  10.0.24.4        4.4.4.4          0x80000007   396  0x28 0xf9e5  32
NSSA     10.0.44.252      4.4.4.4          0x8000000b   656  0x28 0x3309  36

OSPF database, Area 0.0.0.2
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Router   1.1.1.1          1.1.1.1          0x8000001a  1006  0x22 0x8c3c  60
Router  *2.2.2.2          2.2.2.2          0x80000010  2337  0x22 0xd9fa  48
Summary *2.2.2.2          2.2.2.2          0x80000009   337  0x22 0xe044  28
Summary *4.4.4.4          2.2.2.2          0x80000005  1337  0x22 0xfa1b  28
Summary *10.0.24.0        2.2.2.2          0x80000019   737  0x22 0xf5fa  28

nushadu · Answer

ed@vMX-PE1# run show ospf database

OSPF database, Area 0.0.0.2
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Router  *1.1.1.1          1.1.1.1          0x8000001a  1449  0x22 0x8c3c  60
Router   2.2.2.2          2.2.2.2          0x80000010  2782  0x22 0xd9fa  48
Summary  2.2.2.2          2.2.2.2          0x80000009   782  0x22 0xe044  28
Summary  4.4.4.4          2.2.2.2          0x80000005  1782  0x22 0xfa1b  28
Summary  10.0.24.0        2.2.2.2          0x80000019  1182  0x22 0xf5fa  28
OpaqArea*1.0.0.1          1.1.1.1          0x80000008   438  0x22 0x22fd  28
OpaqArea 1.0.0.1          2.2.2.2          0x80000008   982  0x22 0x26f1  28
OpaqArea*1.0.0.3          1.1.1.1          0x80000005  2426  0x22 0x2520 136
OpaqArea 1.0.0.3          2.2.2.2          0x8000000b  2982  0x22 0xa09e 136
    OSPF AS SCOPE link state database
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Extern   10.0.44.252      2.2.2.2          0x80000005  1582  0x22 0xf160  36

[edit]
ed@vMX-PE1#

Gruizzy · Answer

It's a little bit tricky, because without R2, R3 and R5 learn nothing. But as said by certman20, The flooding scope of Type-3 LSA is a single area, so R5 cannot receive any Type-3 LSA from R2. So B is the correct answer.
Please update

Alex321 · Answer

B. 
R3 will receive Type-3 LSA from R2 and then will re-create Type-3 LSA for upper area.

JN0-648 Exam - Question 20

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