CCNP Security Practice Question
A network administrator is implementing IP Source Guard (IPSG) on a Cisco Catalyst 3850 switch to prevent IP spoofing. The administrator enables DHCP snooping and IPSG on VLAN 10. A user connects a laptop with a statically assigned IP address 10.10.10.50/24 and gateway 10.10.10.1. The laptop cannot reach any network resources. What is the most likely reason?
⚠ Common exam trap
The trap here is assuming that IP Source Guard automatically permits statically assigned IP addresses, when it actually requires either a DHCP-learned binding or a manual static binding.
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 Source Guard requires that the IP address be learned via DHCP snooping or be statically configured in an IP source binding.
IP Source Guard relies on the DHCP snooping binding table to validate source IP and MAC addresses. When a device uses a static IP address, no dynamic binding exists, so the switch drops its traffic. To allow the static address, an IP source binding must be manually configured with the ip source binding command, which populates the binding table.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
DHCP snooping must be disabled for IP Source Guard to function with static addresses.
Why it's wrong here
DHCP snooping must be enabled for IPSG to use the dynamic binding table. Disabling DHCP snooping would remove the source of dynamic bindings and break IPSG for DHCP clients. For static addresses, DHCP snooping can remain enabled; you simply add a static binding. Therefore, disabling it is not required and would be counterproductive.
- ✓
IP Source Guard requires that the IP address be learned via DHCP snooping or be statically configured in an IP source binding.
Why this is correct
IP Source Guard uses the DHCP snooping database to validate source IP and MAC addresses. For static IP addresses, an IP source binding must be manually configured using the ip source binding command. Without this binding, the switch drops all traffic from the laptop because it cannot verify the source, causing complete loss of connectivity.
- ✗
IP Source Guard only works with IPv6 addresses, so IPv4 static addresses are not supported.
Why it's wrong here
IP Source Guard supports both IPv4 and IPv6. For IPv4, it validates against the DHCP snooping binding table or static IP source bindings. IPv6 support uses similar mechanisms. The issue is not address family but the lack of a binding for the static IP, so this statement is incorrect.
- ✗
The laptop must be configured with a DHCP address even if a static IP is desired, because IPSG blocks all non-DHCP traffic.
Why it's wrong here
IPSG does not block all non-DHCP traffic; it blocks traffic that does not match an entry in the DHCP snooping binding table or a static IP source binding. A statically configured IP can work if a static binding is added. The requirement is not to use DHCP, but to have a valid binding, so this option is misleading.
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
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JA
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
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.