mediumMultiple Choice
300-410 Practice Question: Given this configuration: ip nat pool GLOBAL…
Given this configuration:
ip nat pool GLOBAL 203.0.113.1 203.0.113.10 prefix-length 28 ip nat inside source list 10 pool GLOBAL overload access-list 10 permit 10.0.0.0 0.255.255.255
What is the effect?
⚠ Common exam trap
Watch out — candidates often confuse `overload` with static NAT or assume `prefix-length` is invalid, but Cisco explicitly tests the understanding that `overload` enables PAT and that `prefix-length` is a valid syntax for defining the subnet mask in NAT pools.
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
✓
Inside hosts matching ACL 10 are translated to addresses in the pool using PAT.
The configuration uses `ip nat inside source list 10 pool GLOBAL overload`, which combines a NAT pool with the `overload` keyword to enable Port Address Translation (PAT). ACL 10 permits all 10.0.0.0/8 addresses, so inside hosts matching this ACL are translated to the pool addresses (203.0.113.1–203.0.113.10) with port multiplexing, allowing many hosts to share the same public IP. This is the standard Cisco PAT behavior, making option C correct.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
All inside hosts are translated to the first pool address only.
Why it's wrong here
The overload keyword enables PAT, so many inside hosts share the pool addresses using unique source ports, not just the first address. It is tempting because without overload the pool would translate to the first address, but overload changes that behaviour to port-based multiplexing across the range.
- ✗
Each inside host gets a unique pool address without port translation.
Why it's wrong here
The overload keyword applies port address translation, so hosts share pool addresses via unique ports rather than receiving a dedicated address each. It is tempting because a NAT pool without overload does assign one address per host, but overload specifically enables PAT sharing here.
- ✓
Inside hosts matching ACL 10 are translated to addresses in the pool using PAT.
Why this is correct
The `overload` keyword enables PAT, allowing many inside hosts permitted by ACL 10 to share the pool's addresses via port multiplexing. The pool spans 203.0.113.1–203.0.113.10, so translations are limited to those ten addresses rather than the full /28 subnet.
- ✗
The prefix-length 28 is invalid; a netmask must be used instead.
Why it's wrong here
Cisco IOS accepts prefix-length in the ip nat pool command; it is the supported alternative to the netmask keyword, so the pool is valid. The option is tempting because NAT pool syntax historically used netmask, but prefix-length 28 is legal and simply defines the pool's subnet mask.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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