V-Wire Interface with NAT Palo Alto Firewall

🛡️ Palo Alto Networks Study Notes

Implementing NAT in a Virtual Wire (V-Wire) Environment

📌 1. Title

Palo Alto PAN-OS: Configuring Network Address Translation (NAT) on Virtual Wire (V-Wire) Interfaces

🧭 2. Brief Overview

These notes explore how Network Address Translation (NAT) works with Virtual Wire (V-Wire) interfaces on a Palo Alto Networks firewall.

Although V-Wire interfaces operate transparently at Layer 2 (without IP or MAC addresses), they can still perform Layer 3 functions, such as NAT—specifically Port Address Translation (PAT)—to enable internet access for internal users.

🌱 3. Beginner Notes (Simple Explanations)

🔁 What is NAT?

NAT (Network Address Translation) is the process of changing one IP address into another as traffic passes through a network device.
Example: converting a private IP (like 192.168.1.10) into a public IP for internet access.

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🔌 What is V-Wire?

A Virtual Wire (V-Wire) is a transparent firewall mode that connects two network segments like an “invisible straw” or a “bump in the wire.”

• No IP address
• No MAC address
• No routing participation

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⚠️ The Challenge

Normally, a firewall needs an IP address on its interface to perform NAT.
But V-Wire interfaces do not have IP addresses.

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✅ The Solution

Even though the V-Wire interface is “invisible,” the firewall can still:

• Inspect traffic passing through
• Apply NAT rules
• Translate IP addresses based on defined policies

⚙️ 4. Intermediate Notes (How It Works & Configuration)

🔍 How It Works

In a V-Wire deployment:

• The firewall does not participate in routing or broadcast domains
• An internal router manages the internal network
• An external router / ISP manages the internet side
• The firewall sits between them, transparently inspecting and translating traffic

🛠️ Configuration Steps (PAN-OS)

Follow these five steps to configure NAT with V-Wire:

1️⃣ Create Zones

• Zone Type: Virtual Wire
• Example: trust-vwire, untrust-vwire

2️⃣ Configure Interfaces

• Interface Type: Virtual Wire
• Assign each interface to its respective V-Wire zone

3️⃣ Create a V-Wire Pair

• Bind the two physical interfaces into a Virtual Wire object

4️⃣ Create a NAT Policy

• Source Zone: Internal V-Wire zone
• Destination Zone: External V-Wire zone
• Translation Type: Translated Address

⚠️ Important:
You cannot use Interface Address because V-Wire interfaces do not have IP addresses.

5️⃣ Create a Security Policy

• Allow traffic between zones (e.g., internal ➜ external)

🧠 5. Advanced Notes (Design & Troubleshooting)

🏗️ Design Insights

• Broadcast Domains:
  V-Wire interfaces do not terminate broadcast domains.
  Traffic remains within the domains created by the surrounding routers.

• PAT Specifics:
  When using Port Address Translation (PAT):

  • You must manually specify a Translated IP address
  • This IP must belong to the external network
  • Example: an IP from the 172.x.x.x range assigned via DHCP

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🧪 Troubleshooting & Verification

✅ CLI Verification

Use the following CLI command:

show session all

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