🖥️ 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.
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