How to Configure Syncthing for Multiple Devices: Peer Networks, Star Topology, and Introducers

Syncthing Series

• How to Use Syncthing: Practical Notes from Device Pairing to File Sync
• Deploy Syncthing with Docker: Compose, Ports, and Volume Mapping
• How to Configure Syncthing for Multiple Devices: Peer Networks, Star Topology, and Introducers
• How to Use Syncthing on Android: Syncthing-Fork Setup and Photo Backup
• How to Manage Syncthing Across Multiple Devices and Folders: Topology, Naming, and Versioning
• How to Sync iPhone Photos to a Computer or NAS with Syncthing

Syncthing uses a decentralized P2P architecture. It does not have a traditional Server or Client role. At the protocol level, every device is a peer.

In real use, though, you can organize it in two common ways:

• Pure peer network: every device pairs directly with the other devices.
• Star network: one NAS, server, or always-on computer acts as the central node, and all other devices pair only with it.

Both approaches fit Syncthing’s design. The difference is management cost and daily workflow.

Understand Peers and the Pseudo Server First

Every Syncthing device has its own device ID. When two devices add each other’s ID and share the same folder, they can sync.

That means Syncthing itself does not require one server to hold all data. What people call a “server” is usually just an always-on device that you choose as the operational center.

For example:

• A NAS is always on and has plenty of storage, so it works well as a central node.
• Phones and laptops often go offline, so they are better treated as edge devices.
• A desktop may be powerful, but it may not run 24/7, so it is usually a normal sync node.

This central node is not a protocol-level server. It is simply the device you let handle management and relay duties in your topology.

Mode 1: Pure Peer Mesh

In pure peer mode, every device pairs with every other device.

For example, suppose you have four devices:

• NAS
• Desktop
• Laptop
• Phone

Each device needs to connect to the other three. Any two online devices can then sync directly.

Advantages:

• Transfer paths are more direct.
• If one device is offline, other online devices can still sync with each other.
• There is no dependency on a single central node.

Disadvantages:

• The more devices you have, the more complex pairing becomes.
• Adding a new device requires confirmation and setup on multiple existing devices.
• Folder sharing relationships can become scattered.

When you only have a few devices, pure peer mode is comfortable. For one computer and one phone, or two computers syncing notes, there is no need to overthink the design.

Once you have five or six devices, maintaining a fully connected mesh by hand becomes increasingly annoying.

Mode 2: NAS-Centered Star Topology

Star topology is usually better for home and personal productivity setups.

Pick one device that stays online, has enough space, and has a stable network connection, such as:

• NAS
• Synology
• Soft router
• Mini PC
• Home Linux server

Then pair every other device only with that center:

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Phone   ----\
Laptop  ---- NAS
Desktop ----/

The phone does not need to pair directly with the laptop, and the laptop does not need to pair directly with the desktop. They all sync indirectly through the NAS.

Advantages:

• Management is simple.
• A new device only needs to pair with the NAS.
• The NAS can handle versioning and backup buffering.
• It fits 24/7 sync scenarios.

Disadvantages:

• If the NAS is offline, other devices may not be able to keep syncing with each other.
• If all traffic goes through the NAS, its network and disk performance affect the experience.
• The central node’s permissions need to be managed carefully.

If you already have a NAS or an always-on mini server, star topology is the default recommendation. It keeps Syncthing’s P2P strengths while making day-to-day management feel much closer to centralized sync.

Basic Order for Multi-Device Setup

No matter which topology you choose, Syncthing setup follows this order:

1. Pair devices first.
2. Share folders second.
3. Confirm the local path on the receiving side last.

Do not start by creating folders everywhere. Clarify device relationships first, and the later steps will be much less chaotic.

Step 1: Pair Devices

Assume you want to connect device A and device B.

Device A could be a phone, while device B could be a NAS or computer.

On device A:

1. Open the Syncthing Web UI.
2. Click Actions in the upper-right corner.
3. Choose Show ID.
4. Copy the device ID or display the QR code.

On device B:

1. Open the Syncthing Web UI.
2. Click Add Remote Device.
3. Enter device A’s ID.
4. Give the device a recognizable name, such as My-Phone.
5. Save.

Then return to device A. It will usually show a prompt saying that device B wants to connect. Accept it.

At this point, the two devices have established a peer relationship, but no folders are syncing yet.

Step 2: Create and Share a Folder

On device A, click Add Folder.

Common fields:

• Folder label: a human-readable name, such as Notes.
• Folder ID: the cross-device identifier. Use stable English names, such as notes.
• Folder path: the real local path on this device.

Then switch to the Sharing tab and select the device B you just paired.

After saving, device A sends a folder sharing invitation to device B.

Step 3: Accept the Share

Open device B’s Web UI and wait a few seconds. You will usually see a prompt like:

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Device A wants to share a folder

Click add, then choose a local storage path on device B.

For example:

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/volume1/notes

Or, in a Docker deployment, a container path such as:

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/var/syncthing/notes

After saving, sync starts.

The paths do not have to match across devices. Syncthing identifies the sync relationship by Folder ID, not by requiring every device to use the same local path.

How to Configure Star Topology

If you use the NAS-centered model, a good setup is:

1. Deploy Syncthing on the NAS first.
2. Pair every phone, computer, and server only with the NAS.
3. Create or accept the main sync folders on the NAS.
4. Each new device only needs to add the NAS device ID.
5. Share each folder only between the NAS and the devices that need it.

For example:

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NAS
├── notes       -> desktop, laptop, phone
├── photos      -> phone, backup disk
├── downloads   -> desktop, NAS
└── scripts     -> desktop, laptop

This keeps the structure clear. You can treat the NAS as the control panel for sync relationships.

What Is an Introducer?

Syncthing has a useful feature called Introducer.

It is designed for multi-device setups.

Suppose you set the NAS as an introducer. Later, when a new device pairs with the NAS, the NAS can introduce the other devices it knows to the new device. It can also help propagate existing shared relationships.

This reduces repetitive clicking and repeated device pairing.

It is useful when:

• You have several computers and phones at home.
• The NAS is the long-running central node.
• You add new devices often.
• You want to reduce manual device relationship maintenance.

Be careful, though. An introducer expands the scope of automatically established relationships. Do not set an untrusted device as an introducer, and do not enable it casually before you understand the topology.

A safer rule is:

• Only set the NAS or main server as the introducer.
• Do not make ordinary phones or laptops introducers.
• After adding a new device, check which devices and folders were added automatically.

Folder Type Controls Data Direction

Syncthing’s permission behavior is mostly controlled by the folder type.

Open a folder’s settings and adjust Folder Type in the options.

There are three common types:

Send & Receive

The default mode. Both sides can send and receive changes.

It is suitable for:

• Editing notes from multiple devices.
• Syncing documents across several computers.
• Normal two-way sync folders.

This is the closest mode to true peer-to-peer sync.

Send Only

This device only sends changes and does not accept changes from other devices.

It is suitable for:

• Data source folders.
• Distributing a primary folder to other devices.
• Preventing remote changes from affecting this device.

For example, you can set a software installer directory on the NAS to Send Only so other computers only receive it.

Receive Only

This device only receives changes and does not send local changes out.

It is suitable for:

• Backup machines.
• Read-only mirrors.
• Preventing local accidental deletion from propagating back to the source.

For example, if the NAS receives photos from a phone, and you do not want phone-side deletion to also remove the NAS copy, you need to design folder types and deletion policy carefully.

Different Folders Can Use Different Topologies

Syncthing topology does not need to be site-wide or uniform. You can design it per folder.

For example:

• notes: desktop, laptop, phone, and NAS all use Send & Receive.
• photos: phone sends, NAS receives and keeps versions.
• downloads: desktop and NAS sync, phone does not participate.
• backup: main computer is Send Only, NAS is Receive Only.

Do not force every directory into one rule. In multi-device sync, the important question is data direction, not device count.

Think About Conflicts and Accidental Deletion Early

The most common multi-device sync problem is not failed setup. It is accidental deletion or conflicts after sync is already working.

Risky scenarios include:

• Two devices edit the same file at the same time.
• A mobile app automatically cleans a folder.
• One device uses the wrong path, creates an empty folder, and syncs it out.
• Cache files, temporary files, workspace state, and real files are synced together.
• Versioning is not enabled on the NAS.

Recommendations:

• Enable file versioning on the NAS for important folders.
• Use .stignore to exclude caches and temporary files.
• Before the first sync of a new folder, test with a small number of files.
• If deletion behavior is unclear, do not set every device to Send & Receive.

Recommended Setup

If you have a NAS or always-on server, use star topology directly:

1. Use the NAS as the central node.
2. Pair the NAS with all devices.
3. Ordinary devices pair only with the NAS.
4. The NAS can be set as an introducer.
5. Choose Send & Receive, Send Only, or Receive Only per folder.
6. Enable file versioning on the NAS for important folders.
7. After adding a new device, share a test folder first to confirm path and permissions.

If you only have two or three devices, and they are often online, pure peer mode is fine. It is more direct and may be faster.

Summary

Syncthing is a P2P peer architecture, but that does not mean every device must be wired into a complex mesh.

Small setups can use pure peer mode. When you have many devices, a NAS, or an always-on host, star topology is usually better. Let the NAS act as the central node and introducer, and let other devices connect only to it. Management becomes much simpler.

The real questions are which devices you trust, which folders need to sync, where data originates, and which device should keep versions after accidental deletion. Topology is just the method. Data flow is the core of the configuration.