Subnets

A subnet is an isolated private network (a VLAN) whose devices can all communicate with each other. By default a subnet is a /24 (254 devices), but the range is configurable: you can give it a larger block (a smaller prefix, e.g. /16) for more devices. /24 is the smallest allowed — StartTunnel rejects a range smaller than /24.

StartTunnel comes with a default subnet, which is sufficient for most users. You can create additional subnets to isolate groups of devices from each other.

Creating a Subnet

1. In StartTunnel, navigate to Subnets and click “Add”.
2. Name the subnet and accept or customize the IP range — the block its devices draw addresses from (a /24 by default, or a larger block). The range is fixed once the subnet is created; everything else can be changed later by editing the subnet.
3. Optionally set the subnet’s DNS resolver, outbound IP, and IPv6 prefix (all covered below).
4. Click “Save”.

DNS

Each subnet resolves domain names through one of three modes, chosen with the DNS field in the Add/Edit dialog:

• Default (VPS provider) — use the resolvers your VPS provides. The simplest option, and the default.
• Device — designate one device already on the subnet as its resolver (at least one device must exist first). Use this to point the subnet at a resolver you run yourself.
• Custom — enter up to three DNS server IP addresses to query directly.

This chooses the upstream resolver the subnet uses. It is separate from the private DNS records StartTunnel serves for your own hostnames — see DNS Records for those.

Outbound IP

If your VPS has more than one public IPv4 address, you can choose which one a subnet’s outbound traffic leaves from — its egress (SNAT) address — with the WAN IP field:

• System default — let StartTunnel choose (masquerade through the server’s primary address). When the address it resolves to is known, it’s shown in parentheses, e.g. System default (203.0.113.10).
• A specific address — pin egress to one of the VPS’s detected public IPv4 addresses.

A single-IP VPS has only one choice, so you can leave this on System default. Individual devices can override their subnet’s choice — see Devices › Outbound IP.

IPv6

A subnet can carry a routed IPv6 prefix so every device on it gets a stable, globally-routable address. Set the IPv6 Prefix field (e.g. 2001:db8:abcd::/64) in the Add/Edit dialog, or leave it blank for none. See IPv6 for prefix sizing, routing, and VPS requirements.

Removing a Subnet

1. Navigate to Subnets, select the subnet, and click “Remove”.

Warning

Removing a subnet disconnects all devices on it. Their WireGuard configs will no longer work.