Top Firewall Concepts Every PCNSE Candidate Should Know

Source: Dev.to

Firewall Basics

• A firewall is a security device that monitors and controls network traffic according to defined rules.
• It acts as a gatekeeper, allowing legitimate traffic while blocking malicious or unauthorized access.
• Understanding how firewalls enforce security policies is a foundational requirement for PCNSE candidates.

Types of Firewalls

Packet‑Filtering Firewalls

• Examine traffic based on source/destination IP addresses, port numbers, and protocols.
• Fast and simple, but lack deep inspection capabilities and are rarely used alone in modern environments.

Stateful Firewalls

• Track the state of active connections.
• Automatically allow return traffic for established sessions, providing greater security than basic packet filtering.
• Palo Alto Networks firewalls fall into this category.

Next‑Generation Firewalls (NGFW)

• Inspect traffic at the application layer, identify users, and scan content for threats.
• Understanding NGFW behavior is critical for PCNSE success.

Planes of Operation

• Control Plane – Handles routing, management, and system services.
• Management Plane – Provides configuration, logging, and monitoring through the web interface or Panorama.

Security Zones and Policies

• Security Zones group interfaces that share similar trust levels. Traffic is allowed or denied based on source and destination zones rather than IP addresses.
• Inter‑zone traffic requires explicit security policies.
• Security Policies define how traffic is handled. Each rule includes a source zone, a destination zone, an application, a service, and an action.
• Rules are evaluated from top to bottom; the first matching rule is applied, making rule order extremely important.
• Understanding default inter‑zone and intra‑zone rules helps prevent accidental traffic exposure.

Application, User, and Content Identification

App‑ID

• Identifies applications regardless of port or encryption, enabling precise control (e.g., allowing “SSL” but blocking “Facebook”).

User‑ID

• Maps traffic to users or groups, allowing policies based on identity instead of IP addresses.

Content‑ID

• Scans traffic for malware, vulnerabilities, spyware, and data leaks.
• Works together with App‑ID and User‑ID to enforce zero‑trust security.

Network Address Translation (NAT)

• Modifies IP addresses as traffic passes through the firewall.
• NAT rules are processed before security policies—a key concept tested in the PCNSE exam.

Decryption

• Most modern traffic is encrypted, limiting visibility without decryption.
• Decryption allows the firewall to inspect traffic for threats hidden inside encrypted sessions.
• SSL Forward Proxy is used for outbound traffic decryption.

Security Profiles

• Add threat prevention to allowed traffic.
• Include Antivirus, Anti‑Spyware, and Vulnerability Protection.
• WildFire analyzes unknown files and delivers real‑time protection against new threats.
• These services also control web access and prevent command‑and‑control communication.

Logging and Monitoring

• Provides visibility into traffic and threats.
• Types of logs: Traffic logs, Threat logs, System logs.
• Tools such as the Session Browser, traffic logs, and packet captures help diagnose issues quickly.

High Availability (HA)

• Ensures minimal downtime.
• HA Modes: Active/Passive, Active/Active.
• Configuration, session, and state synchronization enable seamless failover.

VPN

• Secures traffic across untrusted networks using IPsec.
• Allows users to connect securely from remote locations.
• Knowing encryption, authentication, and key exchange is essential for PCNSE preparation.

Best Practices

• Follow the principle of least privilege.
• Use application‑based policies.
• Attach security profiles to all rules.
• Regularly review and clean up policies.
• Log at session end for visibility.

These practices improve security and align with Palo Alto Networks recommendations.

Exam Preparation Tips

• Master how Palo Alto Networks firewalls process traffic, enforce policies, and prevent threats.
• Combine hands‑on practice with a clear understanding of core concepts.
• Focus on the interplay between zones, policies, NAT, decryption, and security profiles.

By mastering these firewall concepts, you’ll be well‑prepared not only for the PCNSE exam but also for real‑world network security roles.