Tuning a local NAS network adaptor on your PC.

🖥️ Lessons Learned: Optimizing Network Performance Between Windows and Synology NAS

If you've ever found yourself wondering why your lightning-fast Synology NAS isn’t delivering the speeds you expected to your Windows PC, you’re not alone. I recently went down the rabbit hole of **multi-NIC networking**, **Windows routing quirks**, and **Synology access issues** — and came out the other side with a surprisingly lean and fast setup.

Here’s a breakdown of the lessons learned — and what actually worked.

🚧 The Problem: Speed Bottlenecks & Wrong Interface Routing

Even with a high-performance Synology NAS equipped with a 10GbE card, and a PC connected via a 2.5GbE LAN port, I was seeing inconsistent performance — and even security alerts from the Synology when accessing the NAS web interface.

Turns out, the culprit was simple: **Windows was routing NAS traffic over the wrong network adapter** — often defaulting to Wi-Fi or a secondary Ethernet port on a different subnet.

🔧 Lesson 1: Understand the Windows Routing Table

Windows doesn’t always choose the fastest interface — it chooses based on **metrics** (priority numbers), and these can change on reboot or reconnection.

To view your routing table:

```bash

route print

This shows which interface Windows will use for a given destination. If the wrong adapter is prioritized, even local NAS access can go through Wi-Fi, causing unnecessary latency or even subnet mismatches.

### 🛣️ Lesson 2: Add a Static Route to the NAS

To ensure that all traffic to the NAS uses the correct (fast) adapter, add a **persistent static route** targeting just the NAS IP address:

```bash

route -p ADD [NAS IP] MASK 255.255.255.255 [NAS IP] IF [Interface Index] METRIC 5

```

* Replace `[NAS IP]` with the actual NAS IP.

* Use `route print` to find the `[Interface Index]` of your fast LAN adapter.

* The gateway and destination IP can be the same when the NAS is directly connected (e.g., via a dumb switch).

This route forces Windows to send all traffic to that NAS through the correct interface — no guesswork.

📉 Lesson 3: Stop Letting Windows Auto-Assign Metrics

Windows uses **"Automatic Metric"**, which attempts to prioritize interfaces based on link speed and other factors. It's often wrong — especially with mixed wired/Wi-Fi environments.

Manually set the interface metric:

```bash

netsh interface ipv4 set interface "[Interface Name]" metric=50

* Use a **lower metric** (e.g., 5) for your fast LAN adapter.

* Use **higher metrics** (e.g., 50–100) for Wi-Fi and fallback links.

* You can check existing metrics with:

```bash

netsh interface ipv4 show interfaces

This ensures Windows consistently prefers your high-speed link.

⚠️ Lesson 4: Subnet Mismatches Can Trigger NAS Security

If traffic to the NAS web interface comes from an unexpected subnet (e.g., your Wi-Fi network), Synology’s security features may block or flag it as a potential intrusion.

Routing all NAS traffic through the correct interface **eliminates false positives**, avoids login delays, and keeps the experience seamless.

⚡ The Result: Instant File Access, Stable Connections

After applying these fixes:

* JPG previews and media access became noticeably faster

* File transfers reached expected speeds over 2.5Gbps

* Synology no longer flagged normal access as suspicious

* The setup stayed stable even after rebooting

And no extra hardware was needed — just a better understanding of how Windows routes traffic.

🧠 Final Thoughts

You don't need to upgrade everything to 10GbE immediately. By tuning your **network routes** and **interface priorities**, you can unlock the full potential of your existing hardware — especially in mixed environments with multiple adapters or subnets.

If you’re running Windows and a Synology NAS, take an hour to review your routing table and metrics — it might save you hours of unexplained slowdowns or weird security behavior.