A. On R1, enable Level 1 on the ge-0/0/1 interface.  In IS-IS, both levels (Level 1 and Level 2) are enabled by default when you enable IS-IS on an interface 1 .  Level 1 systems route within an area 2 .  If the destination is outside an area, Level 1 systems route toward a Level 2 system 2 . Therefore, enabling Level 1 on the ge-0/0/1 interface on R1 would allow packets to reach from R1 to R3.

D. On R3 enable Level 1 on the ge-0/0/4 interface Similarly, enabling Level 1 on the ge-0/0/4 interface on R3 would allow packets to reach from R1 to R3.

These explanations are based on the IS-IS configuration documents and learning resources available at Juniper Networks 1  and Cisco 3 4 .

The routers that are directly connected to the Dallas and Denver subnets are not advertising the connected subnets.  This can be resolved by redistributing the connected subnets into OSPF 1 .

Option C suggests to configure and apply a routing policy that redistributes the connected Dallas and Denver subnets.  This is correct because redistribution allows routes from one routing protocol to be communicated to another, and in this case, it allows the connected subnets to be advertised through OSPF 1 .

Option D suggests enabling the passive option on the OSPF interfaces that are connected to the Dallas and Denver subnets.  This is also correct because in OSPF, a passive interface is an interface that belongs to the OSPF router, but does not send OSPF Hello packets 1 .  It’s typically used on an interface that you don’t want to use for OSPF adjacencies, but you still want to advertise its IP address 1 . Therefore, enabling passive interface can help in advertising the Dallas and Denver subnets.