350-401 Question #200: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. Which two commands are needed to allow for full reachability between AS 1000 and AS 2000? (Choose two)

Options

• AR1#network 19.168.0.0 mask 255.255.0.0
• BR2#no network 10.0.0.0 255.255.255.0
• CR2#network 19.168.0.0 mask 255.255.0.0
• DR2#network 209.165.201.0 mask 255.255.192.0
• ER1#no network 10.0.0.0 255.255.255.0

Explanation

BGP Network Advertisement Explanation

Options B and C are correct because R2 needs to advertise the 19.168.0.0/16 network into BGP to make it reachable from AS 1000, and the incorrect 10.0.0.0/24 network advertisement on R2 must be removed since it either doesn't exist in R2's routing table or creates a routing conflict - the no network command withdraws that erroneous BGP advertisement.

Why the distractors are wrong:

• A is incorrect because R1 already has a correct configuration or advertising 19.168.0.0/16 from R1 is not the right router to originate that prefix (it belongs to R2's side/AS 2000).
• D is incorrect because 209.165.201.0 /26 uses the wrong subnet mask (255.255.192.0 = /18, not matching the actual network), making it an invalid or mismatched advertisement.
• E is incorrect because removing R1's 10.0.0.0 network advertisement would break connectivity rather than restore it, and that may be a legitimate network on R1's side.

💡 Memory Tip: In BGP, the network command only works if the exact prefix and mask exist in the routing table - always verify the prefix matches precisely, and use no network to clean up any misconfigured advertisements that could cause routing black holes.

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