350-401 Question #560: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. An engineer must configure static NAT on R1 lo allow users HTTP access to the web server on TCP port 80. The web server must be reachable through ISP 1 and ISP 2. Which command set should be applied to R1 to fulfill these requirements?

Options

• Aip nat inside source static tcp 10.1.1.100 80 209.165.200.225 80 extendable
• Bip nat inside source static tcp 10.1.1.100 80 209.165.200.225 80
• Cip nat inside source static tcp 10.1.1.100 80 209.165.200.225 80
• Dip nat inside source static tcp 10.1.1.100 80 209.165.200.225 80 no-alias

Explanation

Explanation

Option A is correct because the extendable keyword is required when configuring static NAT with multiple outside interfaces (ISP 1 and ISP 2). This keyword allows the same inside local address to be mapped to multiple outside global addresses simultaneously, which is essential in a dual-ISP scenario where the web server must be reachable through both ISPs.

Option B and C are incorrect because they use the basic static NAT TCP command without the extendable keyword - this configuration only supports a single outside interface and will fail (or produce errors) when a second ISP mapping is attempted for the same inside address.

Option D is incorrect because no-alias simply prevents the router from creating an ARP alias entry for the translated address - it does not enable the multi-ISP reachability requirement, and the server would still not be properly accessible through both ISPs.

Memory Tip: Think "extend = multiple exits" - whenever you see multiple outside paths (dual ISPs) for the same inside host in a static NAT scenario, you need extendable to stretch that single mapping across both outside interfaces.

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