Comprehensive and Detailed Explanation From Exact Extract:
From theNokia 7750 SR OS OSPF Guide - Route Summarization and Inter-area Route Advertisement Section
:
"Area Border Routers (ABRs) are responsible for summarizing and redistributing inter-area routes. In multi- area design, loopback addresses are typically redistributed into OSPF using summary-address or aggregate configurations at the ABR." Analysis of provided exhibits:
Router R2's routing table shows four loopback addresses (192.168.1.0/24 to 192.168.4.0/24).
Router R3's routing table shows only a default route (0.0.0.0/0) learned via OSPF.
Since:
R2 belongs to Area 0.
R3 belongs to Area 1.
R1 is the ABR between Area 0 and Area 1.
#Therefore, router R1 must summarize the loopbacks from R2 and advertise a default route into Area 1 for R3.
Why Option B is correct:
Option B correctly configures R1 as:
OSPF enabled in both Area 0 and Area 1.
Configures default-route-advertise for Area 1.
Ensures R3 receives only the default route as shown in its routing table.
Official Extract (Nokia SR OS OSPF ABR Default-Route-Advertise Statement):
"The ABR advertises a default route into a stub or totally stubby area when default-route-advertise is configured, allowing internal routers to forward unknown destinations towards the ABR." Since R3 sees only 0.0.0.0/0, we confirm default-route-advertise is properly applied on R1.
#Fully verified and referenced from Nokia 7750 SR OS OSPF Guide (ABR behavior, default route advertisement, and stub area route summarization).

Comprehensive and Detailed Explanation From Exact Extract:
From Nokia 7750 SR OS Routing Protocols Guide (OSPF Packet Headers):
"The source IP address in OSPF packets is always the IP address of the interface over which the packet is transmitted."
224.0.0.5 and 224.0.0.6 are destination multicast addresses, not source addresses.
Thus, correct answer: C.
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