A. R5(config)#router ospf 1
R5(config-router)#no area
R5(config-router)#summary-address 172.16.0.0 255.255.252.0
B. R4(config)#router ospf 99
R4(config-router)#network 172.16.0.0 0.255.255.255 area 56
R4(config-router)#area 56 range 172.16.0.0 255,255.255.0
C. R4(config)#router ospf 1
R4(config-router)#no area
R4(config-router)#summary-address 172.16.0.0 255.255.252.0
D. R5(config)#router ospf 99
R5(config-router)#network 172.16.0.0 0.255.255.255 area 56
R5(config-router)#area 56 range 172.16.0.0 255.255.255.0
Explanation:
Area 36 is a NSSA so R5 is an ASBR so we can summarize external routes using the “summary address”
command. The command “area area-id range” can only be used on ABR so it is not correct.
The summarization must be done on the ASBR which is R5, not R4 so the correct answer must be started with “R5(config)#router ospf 1”.
Note: The “no area” command is used to remove any existing “area …” command (maybe “area 56 range …” command).
range …” command).