A VPN that worked without trouble yesterday and now hangs mid-connection, or refuses to connect at all, is not necessarily broken. The internet connection itself is usually fine. What has often changed is the behavior of equipment sitting between the user and the wider internet - equipment built to examine traffic closely enough to recognize what a VPN looks like, not just where it is going.
That equipment performs what is known as deep packet inspection, or DPI. Ordinary routing cares only about addresses and ports. DPI goes further, examining the start of a connection, the rhythm and size of packets, and sometimes the content of unencrypted data, then deciding whether to let a flow through, throttle it or cut it outright. Operators use this for network management, companies use it for security, and in a number of countries it is deployed nationwide, so filtering happens at the level of the network itself rather than through blocking individual websites one at a time. Independent comparisons, including analysis from outlets such as BuyBestVPN, have tracked how unevenly different protocols survive this kind of scrutiny, since detection methods are rarely applied uniformly across operators or regions. according to BuyBestVPN
What DPI Actually Looks For
Several signals give a VPN away. A blocked IP address defeats any protocol, since no amount of disguise helps if the destination itself is on a blacklist. Many VPN protocols also open with a recognizable handshake - WireGuard, for instance, uses fixed message types and sizes without attempting to hide them. TLS connections carry a ClientHello message that reveals the requested site name in plain text, along with a fingerprint built from cipher suites and extensions; a client that doesn't resemble an ordinary browser stands out immediately. Traffic shape matters too: packet timing and size can expose a TLS connection hidden inside another TLS connection. Even randomness is a clue, since some filtering systems flag data that looks like pure noise from the first byte. Some systems go further still, actively probing a suspected server to see how it responds.
Why Different Transports Behave Differently
No single protocol disguise works everywhere, which is why services built around multiple transport options tend to hold up better under inspection. VLESS Reality borrows the TLS 1.3 handshake of a genuine third-party website, so a probe connecting to the server sees that legitimate site rather than a VPN. VLESS XHTTP carries data as separate HTTP-like upload and download requests layered over Reality, useful where long single TCP connections get cut. Trojan runs over real TLS and behaves like ordinary HTTPS, so an incorrect password simply produces the response of a normal web server. Hysteria2 runs over QUIC with a genuine certificate, resembling HTTP/3, though it depends on UDP passing through the network. Shadowsocks 2022 uses authenticated encryption with no recognizable handshake at all, making it light and fast, but more exposed where filters specifically target random-looking traffic.
Living With an Arms Race That Never Ends
None of these approaches is invisible, and none is permanently unblockable. Filtering systems evolve, and any network operator retains the option of blocking a server's address outright or permitting only a pre-approved list of services. That reality argues against relying on a single protocol and in favor of systems that can test traffic in real time and switch when a connection stops carrying data, rather than trusting a successful handshake alone. Practical steps still help: keep the app current, allow extra time for the first connection on a filtered network, try a different server location, compare behavior across a different network such as home Wi-Fi versus mobile data, and report the operator, region and timing to support teams, since patterns across users often reveal what a single connection log cannot. Rules governing VPN use vary by country, and responsibility for complying with local law rests with the user.
