To reduce the size of OSPF Area 100, you configure the area with the no-summaries parameter. After
committing this configuration change, you notice that an OSPF router in a remote area is no longer receiving
Type 5 LSAs from an ASBR in Area 100.
Which statement is true in this scenario?
A.
The ASBR in Area 100 generates Type 5 LSAs, and they are blocked by the ABR.
B.
The ASBR in Area 100 generates Type 5 LSAs, and a virtual link is required for transport to other areas.
C.
The ASBR in Area 100 generates Type 5 LSAs, and they are transported to Type 7 LSAs.
D.
The ASBR in Area 100 generates Type 5 LSAs, and places them in its own database.
Explanation:
The no-summaries setting prevents the ABR from advertising summary routes into the NSSA.
http://www.juniper.net/documentation/en_US/junos16.1/topics/example/ospf-not-so-stubby-areaconfiguring.html
Junos OS allows you to also restrict type 3 LSAs in NSSA areas using the no-summaries configuration option.
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LSA Type 3: Summary LSA
LSA Type 4: Summary ASBR LSA
https://networklessons.com/ospf/ospf-lsa-types-explained/
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Answer is B.
Type 5 not being blocked, in ASBR it is not generate LSA5 at all.
> show ospf database logical-system ospf-rt
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 120.1.1.1 120.1.1.1 0x80000001 66 0x22 0x41ff 36
Router *120.1.1.2 120.1.1.2 0x80000001 65 0x22 0x3b02 36
Summary 120.1.1.0 120.1.1.1 0x80000002 70 0x22 0xb3a 28
Summary *120.1.1.0 120.1.1.2 0x80000002 69 0x22 0x53f 28
OSPF database, Area 0.0.0.10
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 120.1.1.1 120.1.1.1 0x80000004 66 0x20 0x47f6 36
Router *120.1.1.2 120.1.1.2 0x80000004 65 0x20 0x45f5 36
Network *120.1.1.2 120.1.1.2 0x80000001 70 0x20 0xe169 32
Summary 0.0.0.0 120.1.1.1 0x80000001 66 0x20 0xbafe 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern *120.1.1.0 120.1.1.2 0x80000001 76 0x22 0x1ab0 36
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Think the option has to be C but written back to front.
Currently: The ASBR in Area 100 generates Type 5 LSAs, and they are transported to Type 7 LSAs.
Corrected: The ASBR in Area 100 generates Type 7 LSAs, and they are transported to Type 5 LSAs .
Within an area with some form of “subbiness” the ASBR will generate a type 7 LSA which is then changed to a type 5 by the ABR.
The no-summaries statement will convert the area to a totally stubby area. If we assume this was correctly done…
“Totally NSSA area’s not only block external routes (LSA 4 and 5) from other area’s but also inter-area routes (LSA 3) from other area’s. So it will reduce the size of the database again while still allowing local redistribution using NSSA (LSA 7).”
https://www.inetzero.com/which-area-type-do-you-prefer-normal-stub-totally-stub-nssa-or-totally-nssa/
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Option D, Final answer.
To be able to answer this question correctly, you need to clearly understand the OSPF areas and what they do with reference to ASBR.
Routing devices that exchange routing information with routing devices in non-OSPF networks are called AS boundary routers. They advertise externally learned routes throughout the OSPF AS. Depending on the location of the AS boundary router in the network, it can be an ABR, a backbone router, or an internal router (with the exception of stub areas).
OSPF uses the Link State Algorithm in conjunction with Edsger W. Dijkstra Shortest Path First (SPF) algorithm to send out OSPF advertisements, known as Link-State Advertisements (LSAs), to share its Local Link-State Database (LSDB) with OSPF enabled devices and to create an overall topology of every router, link state and link metric within a network.
Each OSPF router maintains an identical database describing the Autonomous System’s topology. From this database, a routing table is calculated by constructing a shortest-path tree.
Since this is an ASBR, which could also be a backbone router or ABR, The ASBR in Area 100 will generates Type 5 LSAs, and places them in its own database for other ospf area types that may need it such as not-so-stubby-area.
In an NSSA, the AS boundary router generates NSSA external (Type 7) LSAs and floods them into the NSSA, where they are contained. Type 7 LSAs allow an NSSA to support the presence of AS boundary routers and their corresponding external routing information. The ABR converts Type 7 LSAs into AS external (Type 5 ) LSAs and leaks them to the other areas, but external routes from other areas are not advertised within the NSSA.
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Hi everyone,
The question is so misleading.
you notice that an OSPF router in a remote area is no longer receiving
Type 5 LSAs from an ASBR in Area 100.
@chuck, you are correct but the question refers how type-5 routes are seen from other remote Areas. Indeed in an NSSA area type-5 routes comming from other areas are not seen
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