This PCNSE practice question tests your understanding of deploy and configure firewalls. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A firewall is configured with two ISPs for load balancing. Traffic from certain sources should always egress via ISP-1. What is the correct configuration?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
Multiple virtual routers
Why wrong: Virtual routers separate routing domains; they don't enforce source-based egress.
ECMP with route metrics
Why wrong: ECMP distributes traffic based on flow, not source-based persistence.
Policy-based forwarding (PBF) with source criteria
PBF can match source IP and forward to a specific next hop.
Subinterfaces per ISP
Why wrong: Subinterfaces are for VLAN separation, not for forwarding decisions.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Policy-based forwarding (PBF) with source criteria
Policy-based forwarding (PBF) allows you to override the routing table for specific traffic based on criteria such as source IP, destination IP, or application. By configuring a PBF rule with source criteria, you can force traffic from certain sources to always egress via ISP-1, regardless of the load-balancing configuration. This is the correct method for source-based path selection in a multi-ISP setup.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Multiple virtual routers
Why it's wrong here
Virtual routers separate routing domains; they don't enforce source-based egress.
ECMP with route metrics
Why it's wrong here
ECMP distributes traffic based on flow, not source-based persistence.
Policy-based forwarding (PBF) with source criteria
Why this is correct
PBF can match source IP and forward to a specific next hop.
Clue confirmation
The clue word "always" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Subinterfaces per ISP
Why it's wrong here
Subinterfaces are for VLAN separation, not for forwarding decisions.
Common exam traps
The trap here is that candidates often confuse ECMP load balancing with source-based path selection, assuming that route metrics or multiple virtual routers can achieve deterministic egress control, when in fact only PBF provides the necessary policy override for specific source traffic.
Detailed technical explanation
PBF operates by creating a forwarding policy that matches traffic based on Layer 3/4 criteria (e.g., source IP, destination port) and then applies a next-hop or egress interface override, bypassing the FIB. In a load-balanced environment, PBF rules are evaluated before the routing table, allowing granular control. A real-world scenario is a branch office that must route all traffic from the finance subnet through a dedicated MPLS link while using a broadband ISP for general traffic, which PBF handles without requiring complex routing protocol manipulation.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Deploy and Configure Firewalls — This question tests Deploy and Configure Firewalls — Read the scenario before looking for a memorised answer..
The correct answer is: Policy-based forwarding (PBF) with source criteria — Policy-based forwarding (PBF) allows you to override the routing table for specific traffic based on criteria such as source IP, destination IP, or application. By configuring a PBF rule with source criteria, you can force traffic from certain sources to always egress via ISP-1, regardless of the load-balancing configuration. This is the correct method for source-based path selection in a multi-ISP setup.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "always". Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This PCNSE practice question is part of Courseiva's free Palo Alto Networks 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 PCNSE exam.
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