Comprehensive and Detailed In-Depth Explanation:
Understanding the IS-IS Network Structure in the Question:
* IS-IS Area IDs and Router Roles
* Area 49.0001 (Level-1-2): Contains R1, R2, R4 (all Level-1-2 routers).
* Area 49.0002 (Level-1-2 & Level-1): Contains R3 (Level-1-2) and R5 (Level-1 only).
* Key Command Used: ipv6 default-route-advertise always level-1
* This command forces R4 to advertise a default route (::/0) to all Level-1 routers within its area.
* Only Level-1 routers in the same area as R4 will receive the default route.
* Level-2 routers do not receive or propagate this default route unless additional configuration is done.
Route Distribution Analysis:
* R4 (Level-1-2) is configured to advertise a default route to Level-1 routers.
* R1 and R2 (both Level-1-2) are in the same area (49.0001) as R4, so they receive the default route.
* R3 (Level-1-2) is in area 49.0002 but connects to R4 (49.0001), meaning it can receive the default route through its Level-1 connection.
* R5 (Level-1 only) is in area 49.0002, but R4 does not propagate the default route to another Level-
1 area (49.0002).
* Since R5 is a Level-1 router and does not have a Level-2 connection, it cannot receive the default route from R4.
Final Conclusion:
# R1 receives the default route.# R2 receives the default route.# R3 receives the default route.# R5 does NOT receive the default route.
Thus, the correct answer is: C. R5.