mediumMultiple Choice
CCNP Practice Question: The purpose of the 'ip nat inside source list'…
What is the purpose of the 'ip nat inside source list' command in Cisco IOS?
⚠ Common exam trap
Test-takers frequently confuse 'ip nat inside source list' with 'ip nat inside' (which defines the inside interface), leading them to select option A, but the 'source list' specifically ties an ACL to a translation method, not the interface role.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It identifies the traffic to be translated and the translation method.
The 'ip nat inside source list' command is used to define which traffic (identified by an access list) should be translated and to specify the translation method, such as dynamic NAT, PAT, or static NAT. It links the ACL that matches the source IP addresses to a NAT pool or interface, enabling the router to perform the translation for outbound traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It defines the inside interface for NAT.
Why it's wrong here
The command 'ip nat inside source list' does not define the NAT inside interface; that is done with the interface-level command 'ip nat inside'. The access-list in the NAT command only selects which source addresses are eligible for translation, not which interface is inside. Thus, this option confuses interface role configuration with traffic selection.
- ✓
It identifies the traffic to be translated and the translation method.
Why this is correct
The access-list referenced by 'ip nat inside source list' identifies the traffic that will be translated, while the accompanying pool or interface keyword defines the translation method, such as dynamic NAT, PAT, or static mapping. The ACL matches source IP addresses and the subsequent parameters determine how those addresses are translated. Therefore, this command properly ties the match criteria to the translation action.
- ✗
It filters inbound traffic before NAT is applied.
Why it's wrong here
This access-list is not a security filter and does not inspect or drop traffic based on inbound direction; it merely classifies which inside source addresses should be translated when the packet exits the outside interface. Inbound filtering is accomplished separately with an access-group applied to an interface using 'ip access-group', which evaluates packet headers independently of NAT. The NAT ACL has no effect on permitting or denying traffic—it only influences translation eligibility.
- ✗
It configures the router as a DHCP server.
Why it's wrong here
DHCP server functionality is configured with commands like 'ip dhcp pool' and 'network', which define address pools and options to distribute to clients. The command in question is part of the 'ip nat' configuration and is used solely for address translation, not for allocating IP addresses. Although DHCP and NAT often coexist on the same router, this specific command does not enable DHCP services.
Visual reference
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.