Tor Bridges Guide — obfs4 vs. Snowflake & Fixing 0xF0 / 0xF2 Errors

When Tor Browser stalls at 10% bootstrap or throws an 0xF0 code, the first guess is usually wrong: the site is rarely dead — the path to it is. The honest suspects are your provider or firewall dropping Tor's public entry relays, a system clock drifted out of the descriptor's time window, or a stale circuit that needs a rebuild — and only the first of those is what a Tor bridges guide is for: disguising your way onto the network when the public guard list is blackholed.

The other two fixes cost nothing: sync your clock to UTC, or press Ctrl+Shift+L for a fresh circuit. Picking the wrong fix is the usual failure — people hunt for a new mirror while their clock is off, or fight bridge settings when their ISP never blocked anything.

Updated

When You Need a Bridge — and When a Bridge Actually Hurts Speed

You need a bridge when the path to the Tor network itself is filtered — not when one onion site is slow. Public guard relays are listed in a consensus anyone can download, which makes blocking them a copy-paste job for an ISP, a corporate firewall, a university network, or a national filter. A bridge is simply a relay that is not on that public list, and a pluggable transport is what disguises the fact that you are speaking Tor to it.

Public guard relay

Listed in the public consensus → trivially blockable by any DPI box or IP filter. Fastest possible entry when it is reachable — the default and the right choice on an unfiltered connection.

Bridge + pluggable transport

Unlisted entry, handed out in small batches so scrapers cannot enumerate it → survives IP blacklists. The transport scrambles the handshake so the wire shows WebRTC noise or random bytes instead of Tor.

What a bridge does not do is make you more anonymous to the service you reach: inside the network nothing changes, and the destination cannot tell a private bridge from a listed guard. The bridge only changes who sees you connect — the bridge operator sees your IP instead of a public guard, and your ISP sees obfuscated noise instead of a Tor handshake. If your provider is not blocking Tor, a bridge costs you speed and nothing else: bridges are smaller, busier machines, the obfuscation adds overhead, and you take capacity from people behind real censorship who need it.

Comparing Pluggable Transports: obfs4 vs. Snowflake vs. meek-azure

Three built-in ways to disguise the handshake — pick by what your censor can see and how much speed you will trade

Transport Your traffic looks like Speed Best when
obfs4 Random bytes with no TLS fingerprint — DPI sees noise, not a handshake Fastest of the three ISP-level Tor blocking and you hold a fresh bridge line
Snowflake A WebRTC video call through a volunteer's browser Middling; hates packet loss Regions where requesting bridge lines is itself difficult — no string to paste
meek-azure Ordinary HTTPS to a big CDN via domain fronting Slowest — every byte detours through the CDN Hard firewalls that whitelist only major cloud providers

obfs4 wraps the Tor handshake in a randomized layer: the cert= field in your bridge line authenticates the bridge to you, and on the wire there is no TLS signature for DPI to match. Its one weakness is the bridge's IP itself — once discovered, it can be blackholed like any host — which is exactly why bridge lines are rationed.

Snowflake borrows volunteers' browsers and extensions as throwaway proxies, so your session looks like a video call to an IP that changes constantly; blocking every volunteer means blocking ordinary WebRTC users. It needs no bridge line — choose it directly in Tor Browser's connection settings — but it adds latency and can stall on strict NATs.

meek-azure hides inside a request to Microsoft's CDN: to the firewall it is HTTPS to a domain nobody can afford to block. It is the fallback for when obfs4 and Snowflake are both burned — functional, safe to enable, and the slowest option by a wide margin.

Where Fresh obfs4 Bridge Lines Actually Come From

BridgeDB rations bridges on purpose — four official channels, all free

  1. Inside Tor Browser: Settings → Connection → Bridges → Request a bridge solves a captcha and drops obfs4 lines straight into your settings — the cleanest path and the one least likely to leak metadata.
  2. The BridgeDB web portal at bridges.torproject.org runs the same flow in a browser: captcha in, three bridge lines out.
  3. Telegram: the @GetBridgesBot account returns fresh lines in chat. Only trust that exact handle — lookalike bots harvest requests.
  4. Email: write to bridges@torproject.org from a Gmail or Riseup address with get transport obfs4 in the body, and lines arrive by reply. The provider restriction exists so mass-scraper accounts cannot farm the pool.

A real obfs4 line carries four fields — the bridge's IP:PORT, its 40-hex-character fingerprint, a cert= certificate the obfs4 handshake needs, and an iat-mode packet-timing flag: 

obfs4 192.0.2.15:443 A1B2C3D4E5F6A7B8C9D0E1F2A3B4C5D6E7F8A9B0 cert=Kq4sQ+G9zNfJ6vV8xL2mP7wR3tY5uI1oP0aS4dF6gH8jK2lZ5xC7vB9nM3qW iat-mode=0

Format only — the example sits in the RFC 5737 documentation range. Paste lines whole into the Custom bridges box, one per line; a truncated cert= field is the usual reason a pasted bridge silently fails.

Decoding the Onionsite Error Codes: 0xF0 Through 0xF7

Each code names the handshake stage that broke — read it before assuming the site is gone

Code What it means Working fix
0xF0 Not Found Descriptor absent from the HSDirs — the service is down, the address rotated, or your clock is off so the lookup hits the wrong time-period bucket Sync the system clock to UTC first, then check a signed mirror list
0xF1 Cannot Be Reached Descriptor exists but every introduction point is dead — typically DDoS saturation or the service restarting Wait and retry, or switch to a backup mirror
0xF2 Disconnected The service dropped the rendezvous mid-handshake — congestion or a dying relay Ctrl+Shift+L for a fresh circuit, retry two or three times
0xF3 Unable to Connect Generic rendezvous failure under load — the vague one New circuit, patience, alternate mirror
0xF4 Requires Auth The service demands a client-authorization key — it is working, it just doesn't know you Nothing broken; you need the service's client key
0xF5 Auth Failed Your client-authorization key was rejected or has expired Re-import the correct key in Settings → Onion Services
0xF6 Invalid Address The hostname failed the v3 checksum — a copy error, not a network problem Re-copy the full 56 characters from the source
0xF7 Timed Out Circuit creation keeps timing out before rendezvous completes Check clock skew again, then connectivity; a bridge may help

Clock skew deserves the top spot because it is the least intuitive: v3 descriptors are published under a rotating time period, and a system clock off by more than the window makes the client ask the HSDirs for a descriptor that, from their perspective, does not exist yet — so they truthfully report 0xF0 while the site is perfectly healthy. The two-byte checksum behind 0xF6 is the same mechanism covered in the v3 address anatomy, working as designed.

For the common 0xF0–0xF3 family the order that works is: clock check, then Ctrl+Shift+L (New Tor Circuit for this Site) two or three times, then a secondary mirror from a PGP-signed list — the signed onion address reference is the safe version of that instinct, because searching for a "working mirror" mid-outage is how people land on clones. And if Tor Browser never finishes bootstrapping at all, no onion site was ever the question: the block sits between you and the network, so revisit the bridge and transport settings our Tor & OPSEC safety guide walks through.