Direct P2P vs Bolt Tunnel: How BoltShare Moves Your Files

When you drop a file into BoltShare, the send screen asks you to pick a transfer mode: Direct P2P or Bolt Tunnel. Both get your file to the other person without a size limit and without storing it anywhere. They take different routes, though, and the route matters for speed, reliability and privacy. This post explains what happens in each mode.

The part both modes share: the share link

Whichever mode you pick, the first step is the same. Your browser asks our signaling server for a session and gets back a random token. That token becomes your share link, something like boltshare.in/receive/abc123….

When the receiver opens the link, the signaling server introduces the two browsers to each other. It also tells the receiver the file name and size, so they know what they’re accepting. That is the signaling server’s whole job. It never touches the file itself, and it forgets the session within minutes after both of you leave.

Direct P2P: browser to browser

In Direct P2P mode, the two browsers use WebRTC to open a connection straight to each other. WebRTC is the same technology that powers video calls in your browser.

1. Each browser asks a public STUN server, “what does my connection look like from the outside?”
2. The browsers swap those answers through the signaling server.
3. They try candidate routes until one works, then open an encrypted data channel.

From then on, the file moves in chunks directly from the sender’s device to the receiver’s. WebRTC encrypts every packet with DTLS, so no one in the middle can read it. That includes us, because we’re not in the middle.

Pick Direct P2P when:

• you want file contents to never pass through anyone else’s servers;
• both people are on home Wi-Fi or ordinary mobile data;
• you’re on the same local network, where direct transfers can be very fast.

The catch: some networks don’t allow direct connections. Corporate firewalls, university networks and some mobile carriers (especially those using carrier-grade NAT) can block the route. Then the connection either falls back to a TURN relay, which forwards the still-encrypted packets, or fails to start.

Bolt Tunnel: streamed through a relay

Bolt Tunnel is the default mode because it works on almost any network. Instead of finding a direct route, both browsers open a secure WebSocket (wss://) to our relay, which runs on Cloudflare’s global network. The sender streams the file in 1 MB pieces. The relay forwards each piece to the receiver the instant it arrives.

A few details make it hold up on huge transfers:

• Nothing is saved. The relay holds each piece in memory only long enough to pass it on. There’s no disk, no bucket, and no copy left behind.
• Flow control. The receiver acknowledges what it has written to disk, so a fast sender can’t flood a slow receiver.
• Automatic resume. If either side’s connection drops, whether from Wi-Fi switching, a laptop lid closing or the relay restarting, both browsers reconnect and pick up from the last confirmed byte instead of starting over.

Pick Bolt Tunnel when:

• Direct P2P won’t connect or keeps stalling;
• you’re on an office, school or hotel network;
• you’re sending something very large over an unreliable connection, where resuming matters more than raw speed.

The trade-off: Bolt Tunnel connections are encrypted between each browser and the relay (TLS), not end to end. Our relay never logs or stores file data, but the bytes do pass through it. If that matters for what you’re sending, use Direct P2P, or encrypt the file first (for example, a password-protected 7-Zip archive).

Side-by-side

	Direct P2P	Bolt Tunnel
Route	Device → device	Device → relay → device
Encryption	DTLS, end to end	TLS to and from the relay
Works behind strict firewalls	Sometimes	Almost always
Resumes after disconnects	Yes	Yes
File stored on a server	Never	Never
Size limit	None	None

Either way: keep the tab open

Neither mode stores your file, so the sender’s browser is the source. If you close the tab before the transfer finishes, there’s nowhere left to download from. Keep BoltShare open until the receiver’s progress bar reaches 100%. On a phone, keep the screen on as well, because mobile browsers pause background tabs aggressively.

Where the received file goes

On the receiving side, BoltShare writes the file straight to your Downloads folder as it arrives. It doesn’t build the whole file in browser memory first, which is how multi-gigabyte transfers can finish without crashing the tab.

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Have a question about how BoltShare handles your data? The privacy policy covers it in plain language, or you can contact us directly.