How to Route Traffic Through a Specific Interface on Windows?

How to Route Traffic Through a Specific Interface on Windows

Routing traffic through a particular interface is a powerful technique used in networking when you want to control the exact path your traffic takes, especially on systems with multiple network interfaces (like VPNs, virtual adapters, or multiple NICs).

Fig: How to Route Traffic Through a Specific Interface on Windows

✅ Step-by-Step Guide

🔹 Step 1: Identify the Interface Index (ifIndex)

Run this command in Command Prompt (as Administrator):

netsh interface ipv4 show interfaces

📋 What It Shows:

Interface Index (used in routing)
MTU
Admin State
Interface Name (e.g., Ethernet, Wi-Fi, VPN Adapter)

🔹 Step 2: Add a Persistent Static Route

Use this command format:

route -p add <destination IP> mask <subnet mask> <gateway IP> metric <value> if <interface index>

📌 Example:

route -p add 5.161.76.207 mask 255.255.255.255 192.168.32.1 metric 1 if 20

🧠 What This Means:

5.161.76.207: Destination IP address
mask 255.255.255.255: Targeting a single host
192.168.32.1: The gateway (must be reachable via interface 20)
metric 1: High priority route
if 20: Use interface index 20 (from step 1)
-p: Make the route persistent (stays after reboot)

🔹 Step 3: Verify the Route

Run:

route print

This shows your full routing table. Look for the new route under Persistent Routes.

🔹 Step 4: Remove the Route (if needed)

route delete 5.161.76.207

💡 When to Use This

Directing VPN or proxy traffic through a specific adapter
Testing traffic flow for troubleshooting
Forcing a certain interface for secure or controlled routing
Avoiding default routes in split tunneling scenarios

🛡️ Important Notes:

Make sure the gateway IP is reachable from the chosen interface.
Be cautious — incorrect routes can break connectivity.
Always test the configuration using ping, tracert, or curl.

📦 Conclusion

Manually setting static routes gives you granular control over traffic flow on Windows. It’s a must-know trick for network engineers, penetration testers, and system admins working with multiple NICs, VPNs, or test labs.