You need to create a dynamic NAT pool named Todd that can provide exactly 30 usable global IPv4 addresses. Which ip nat pool command correctly defines the pool range and netmask on a Cisco router?

Introduction / Context:
Dynamic NAT on Cisco routers uses pools of public or global IP addresses, allowing inside private addresses to be translated as needed. When defining a pool, you must choose a start and end address and an appropriate netmask. In this question, the goal is to create a pool named Todd that offers exactly 30 usable global addresses, so you must carefully evaluate the address range and netmask combination that delivers this number.

Given Data / Assumptions:

The pool is named Todd.

Candidate pool ranges are given, for example 171.16.10.65 to 171.16.10.94.

You want 30 usable addresses in the pool.

The ip nat pool command requires a netmask parameter that matches the block of addresses.

Concept / Approach:
The range 171.16.10.65 through 171.16.10.94 contains 30 addresses because 94 minus 65 plus one equals 30. The underlying subnet for this range in a typical design would be 171.16.10.64 slash 27, whose subnet mask is 255.255.255.224. A slash 27 network has 32 addresses total, from 171.16.10.64 to 171.16.10.95, but you can choose to use only a subset of this block in your NAT pool. The netmask given in the pool command must reflect the actual subnet mask of the public network segment, not merely the count of addresses you wish to use.

Step-by-Step Solution:
Count the addresses in the candidate range 171.16.10.65 to 171.16.10.94. The difference is 29, and adding one gives 30 addresses, meeting the requirement. Identify the subnet to which this range belongs. The natural slash 27 network boundary around these addresses is 171.16.10.64 to 171.16.10.95, corresponding to subnet mask 255.255.255.224. Confirm that 255.255.255.224 is therefore the correct netmask for this public block. The correct ip nat pool command should therefore read ip nat pool Todd 171.16.10.65 171.16.10.94 netmask 255.255.255.224. Compare with options and see that option b matches exactly.

Verification / Alternative check:
You can verify the mask and range by converting 255.255.255.224 to binary to see that the increment in the last octet is 32, giving ranges that start at .0, .32, .64, .96 and so on. The block starting at 171.16.10.64 is valid, and 65 through 94 sit inside it. Using this subnet mask in the pool command tells the router how the global addresses are structured on the public side network.

Why Other Options Are Wrong:
Option a uses netmask 255.255.255.240, which is a slash 28 mask with a block size of 16 addresses. That does not match a range of 30 addresses and would be inconsistent with the actual subnet structure.

Common Pitfalls:
Option c uses the same range and netmask as option b but changes the pool name to lowercase todd, which is a different identifier. Names are case sensitive, so this does not match the requirement exactly.
Option d defines a huge range from 171.16.10.1 to 171.16.10.254 with netmask 255.255.255.0, which provides far more than 30 addresses and may not be valid on the connected public network segment.
Option e uses the full subnet range 171.16.10.64 to 171.16.10.95, which is 32 addresses, not the requested 30, so it does not answer the question precisely.

Common Pitfalls:
Students sometimes try to make the netmask match the number of addresses in the pool instead of the actual network design on the global side. Remember that NAT pools sit inside real subnets with fixed masks, and the chosen pool range must be compatible with that subnet. Correctly matching block sizes, network boundaries and address counts is an essential NAT design skill.

Final Answer:
The correct definition is ip nat pool Todd 171.16.10.65 171.16.10.94 netmask 255.255.255.224, which allocates 30 global addresses from a slash 27 subnet.