Suddenly your NAS is inaccessible, your files are all there but you just can't connect? The investigation ideas are all here

 [Computer/Phone] → [Router/Switch] → [Network Cable] → [NAS itself]

Quick judgment method:

1. open your phone (connected to the same LAN WiFi) and see if you can access the NAS web management page
2. if the phone has access to → problem on the computer
3. phone can't access → continue to investigate

2. Troubleshoot the first stop: the IP and network status of the NAS

log in to the NAS background (usually find.synology.com or vendor discovery tools) to view the network status, focusing on:

• IP Address : Did you get the IP address of the 192.168.x.x segment?

  • got the APIPA address (169.254.x.x) → there was a problem with DHCP
  • IP Yes 0.0.0.0 → the NIC does not acquire properly IP

• network port status :

  • light does not turn on → Check the network cable or router port
  • light on but orange/yellow → can be a 100 gigabit negotiation issue

• DNS and gateway : these two must be right, one must be

  • Ping Gateway IP (for example, 192.168.1.1) tests connectivity
  • Ping Test the Internet
  connection with an external IP (such as 114.114.114.114_)

Common error states:

IP: 192.168.1.100 ✅ Normal DNS: 192.168.1.1 ✅ Normal Gateway: 192.168.1.1 ✅ Normal 

If the DNS or gateway is lost, manually fill it in and save it to restart the network service.

3. Check the second stop: Is the service running normally?

NAS access depends on specific services (Samba / NFS / AFP / SFTP, etc.), and service crashes or not starting are the most common "unconnected" reasons.

Synology Troubleshooting Method:

Rapid Test:

Windows Users: Press Win+R →\\NAS-IP< to test directly SMB

• Mac Users: Finder → go to the → connection server → smb://NAS-IP

service is obviously turned on but still can't connect? Check for the following conflicts:

• router or optical cat turned on UPnP but SMB 445 port is occupied
• computer has antivirus/firewall installed blocks SMB traffic (common in 360, Tinder)
• SMB version is not compatible: Synology 7.x disables SMBv1 by default, and old computers need to turn on compatibility

4. Troubleshoot the third stop: router side factors

router is the most overlooked "black box" for NAS access, and the following settings can directly cause the NAS to be unable to connect

1. AP Isolation

some routers have AP isolation enabled by default, and devices on the same LAN cannot access each other, so the NAS cannot be connected.

check: Router background → Wireless settings → Turn off AP isolation

2. VLAN / Guest Network Isolation

if the NAS is connected to the guest network and the computer is on the main network, the two networks are isolated and cannot communicate with each other.

Check: Put the NAS and PC on the same network (same VLAN

3. Port Forwarding/Firewall Rules

some routers have strict default firewall rules that block ports like SMB/NFS.

Quick Verification: router turns off the firewall (or set it to Passthrough) to test whether the NAS can be accessed. Access → to troubleshoot firewall rules step by step.

4. DHCP address pool exhausted

router has too many connected devices, the IP address pool is exhausted, and the NAS may not be assigned IPs.

check: the router's DHCP client list to see if the NAS is in it.

5. Troubleshoot the fourth stop: physical layer problems (easiest to ignore)

1. Network cable problems

the network cable is broken or the crystal head is aging, the surface is not visible, but it will cause the time to pass.

• a network cable that is known to be normal for testing
• Check if the NAS LAN indicator is flashing normally

2. Router port problems

router LAN port may age after long-term use.

• switch to a NAS to connect to other LAN ports
• Switch Bypass Test: NAS → Switches → Routers

3. Network card negotiation problem

NAS Negotiation with the router fails, and it may be downgraded to 10Mbps or half-duplex.

• Manually set NAS NIC speed: Synology → Control Panel → Network → LAN → Manually set the speed to 1000Mbps full-duplex

6. A command to quickly locate the problem

open Terminal (Win: CMD / Mac: Terminal) on your computer and enter:

# Windows arp -a # Mac / Linux arp -a | grep  

see if there are ARP entries:

• have an ARP entry → the link layer is fine, the problem is at the application layer (service/firewall)
• there are no ARP entries → the physical layer or switch layer is not connected, and the network cables and ports are checked section by section

7. Ultimate solution: Reset NAS network configuration

If all the above methods still don't work, you can reset the network configuration of the NAS (without affecting the data):

use the vendor's Discovery tool to rediscover the NAS and reconfigure the IP and services.

8. Summary: Record this chain in the order of investigation

 first determine the segment, check the NAS IP →→, check the service status→ check the router settings, check the → physical layer 

• 80% of "not connecting" issues are due to IP get failed or SMB service exceptions
• 10% is in router AP isolation or firewall
• 10% are physical layer issues (network cables/ports)

remember this order, and if you encounter problems, you can basically solve them by yourself, so you don't have to rush to find after-sales.