300-410 Infrastructure Services Practice Question
A network engineer is configuring a Cisco IOS XE router as a Dynamic Host Configuration Protocol (DHCP) server for a guest wireless subnet. The router must dynamically allocate addresses from the 192.168.50.0/24 pool, but the first 30 addresses must be reserved for static assignment to access points and controllers. Which command must be issued to prevent the DHCP server from offering those addresses?
⚠ Common exam trap
The trap here is assuming that a subnet mask can be appended to the ip dhcp excluded-address command or that the pool network statement can exclude addresses.
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
✓
ip dhcp excluded-address 192.168.50.1 192.168.50.30
The ip dhcp excluded-address command with a start and end address prevents the Cisco IOS XE DHCP server from offering that range from any pool. This correctly reserves the first 30 addresses for static assignment while allowing the rest of the /24 to be leased dynamically. Other commands either restrict the pool incorrectly, introduce invalid syntax, or create static bindings instead of exclusions.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
ip dhcp excluded-address 192.168.50.1 192.168.50.30
Why this is correct
This command globally excludes the range 192.168.50.1 through 192.168.50.30 from any DHCP pool on the router. In this scenario, it ensures the server never offers those addresses, leaving them available for manual static configuration on access points and controllers while the remaining addresses in 192.168.50.0/24 are dynamically leased.
- ✗
ip dhcp pool GUEST network 192.168.50.0 255.255.255.224
Why it's wrong here
Defining the pool network as 192.168.50.0 with a /27 mask limits the allocatable range to 192.168.50.1–192.168.50.30, which is the opposite of the requirement. This would make the server offer only the first 30 addresses, conflicting with the need to reserve them for static devices. The correct approach is to exclude that range while keeping the full /24 pool.
- ✗
ip dhcp excluded-address 192.168.50.1 192.168.50.30 255.255.255.0
Why it's wrong here
The ip dhcp excluded-address command does not accept a subnet mask argument. Including 255.255.255.0 causes a syntax error, so the exclusion is not applied. The command only takes a start and optional end IP address. To reserve the first 30 addresses, the engineer must use the two-address form without a mask.
- ✗
ip dhcp pool GUEST address 192.168.50.1 192.168.50.30
Why it's wrong here
The address command inside a DHCP pool is used for manual bindings to specific clients, not for excluding a range. Configuring it this way would create static host entries for the first 30 addresses rather than preventing their dynamic allocation. It does not achieve the goal of reserving those addresses for external static assignment.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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