Difficulty: Easy
Correct Answer: prefix-length
Explanation:
Introduction / Context:
Dynamic NAT typically requires defining a pool of global (translated) addresses. Cisco IOS lets you specify the pool's subnet mask either as a dotted-decimal netmask or by an alternative parameter. Knowing both forms is useful for speed and accuracy.
Given Data / Assumptions:
Concept / Approach:
The ip nat pool command supports either netmask a.b.c.d or prefix-length n, where n is the CIDR length (for example, 24 for 255.255.255.0). There is no slash notation in the command itself; you spell out prefix-length.
Step-by-Step Solution:
Verification / Alternative check:
Use show running-config to confirm that the pool reflects the intended prefix length. Test with live traffic or show ip nat translations.
Why Other Options Are Wrong:
Slash notation (A) is not literal CLI syntax for this command.
“No mask” (C) would be invalid; a mask is required.
“Block-size” (D) is unrelated to ip nat pool mask notation.
Common Pitfalls:
Typing area-style slash prefixes as in OSPF; mixing up pool prefix with inside interface subnet; forgetting to allow traffic with the correct ACL or route-map.
Final Answer:
prefix-length
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