Great firewall china https traffic disruption

Imagine you’re working on an important online meeting—or uploading sensitive files to a server abroad—and suddenly your secure connection drops or slows dramatically. You check everything on your side: your browser shows the “lock” icon, you’re using HTTPS, and yet things aren’t working. If you were in or connecting through China during one specific hour on August 20 2025, that scenario came pretty close to reality.

The internet is built on trust and encryption. HTTPS connections (secure web traffic) are the backbone of modern commerce, communication, and privacy. When such traffic gets disrupted at a national level, it raises deep questions: How secure is global connectivity? What happens when a major internet-censoring system decides to block or throttle encrypted traffic? And what can users, businesses, and operators do to prepare?

In this article I’ll walk you through what the Great Firewall of China (GFW) is, how the recent disruption of HTTPS (port 443) traffic occurred, what that means technically and socially, and what you should keep in mind if you’re reliant on China-involved internet links. I’ll also share personal reflections and explain the practical implications — no jargon, just conversational clarity.

What is the Great Firewall of China (GFW)?

The name “Great Firewall of China” is pretty evocative. It plays on the idea of the Great Wall of China and a digital firewall, meaning a barrier between the internet inside China and the wider web.

Technically, the GFW is not a single device. It’s a combination of laws, regulations and network equipment operated by the Chinese government and internet service providers inside China. Its job: to monitor, filter, block or slow traffic that the authorities view as sensitive or undesirable.

Some of the core functions of the GFW include:

• Blocking access to selected foreign websites (e.g., Google, Facebook, Twitter)

• Slowing or restricting traffic that crosses China’s national borders (so-called cross-border traffic)

• Deep packet inspection (DPI) of network traffic to detect keywords, protocols or patterns that are deemed sensitive

• DNS tampering or “poisoning”, where domain name lookups are redirected or broken

From my perspective, what’s interesting is that it both shapes the user experience inside China and affects anyone trying to interact with China from outside. If you’re trying to access a site hosted abroad from inside China, or serve a Chinese user from abroad, the GFW is a factor you must consider.

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The HTTPS traffic disruption incident

Here’s where things get interesting.

On the night of August 20 2025 (Beijing Time, UTC+8) something unusual happened. For approximately 74 minutes (from around 00:34 to 01:48) many HTTPS connections between China and the rest of the world were disrupted.

Let’s break down what was reported:

• The standard HTTPS port — TCP port 443 — was the target of the disruption. That’s the port most web browsers use when sending secure traffic.

• The disruption involved the injection of forged TCP RST+ACK (reset + acknowledgment) packets by the GFW devices. In simple terms: instead of letting the secure connection handshake finish, a network device pretended the connection must be torn down.

• The interesting part: only port 443 was affected (ports 22, 80, 8443 and others were apparently not hit) during that event.

• The device fingerprinting suggested the censoring equipment involved did not match previously known GFW devices — meaning it might have been a new piece of hardware or a mis-configured one.

• During the outage, Chinese users reported that foreign websites and cloud services didn’t load, and there were increases in latency for many SaaS applications.

From my viewpoint this disruption stands out because it was targeted at encrypted traffic (HTTPS) and at an essential port — not just blocking a language or keyword, but essentially severing secure connectivity. It raises the question: was this a test of the censorship system, a mis-configuration, or something else? The public analysis is inconclusive.

Technical mechanics of the disruption

Let’s walk through the mechanics in plain language.

What is HTTPS and port 443?
HTTPS (Hypertext Transfer Protocol Secure) is the protocol used when you see the “lock” icon in your browser. It encrypts the communication between your browser and the website, so third parties can’t easily intercept or tamper with it. Most browsers default to connecting via TCP port 443 (though technically other ports can be used).

Because HTTPS is encrypted, censorship systems like the GFW have a harder job — they can’t easily read the content directly, so they rely on network behaviour, packet inspection, protocol features and more subtle signs to detect something they deem undesirable.

What happened during the event?
Here are the key findings from the investigation by GFW Report:

• In traffic originating from inside China to outside, both the SYN packet (client’s request to open connection) and the SYN+ACK response (the server’s acknowledgement) triggered three forged RST+ACK packets each.

• In traffic coming from outside China to inside, only the server’s SYN+ACK triggered the forged RST+ACK packets; the client’s SYN did not.

• The forged RST+ACK packets had certain fingerprints (sequence numbers, window sizes) that did not match the known equipment used by the GFW.

• After about 74 minutes the system returned to normal.

In simpler analogy: imagine you knock on a locked door (SYN). Instead of it opening or asking you for your name (SYN+ACK), a security guard immediately says “no entry” (RST) and slams the door shut. Repeat this for many knocks and you effectively cut off access—even if everything else is working.

Why is this significant?

• Because HTTPS is foundational, blocking it widely is more disruptive than blocking a single website or a protocol like SSH.

• The fact that only one port (443) was targeted suggests either an experiment or a narrowly scoped mechanism (maybe to see how far they could push).

• It highlights that censorship infrastructure is evolving — the fact a new or unknown device was used suggests upgrades or changes are underway.

• For connectivity engineers and businesses, it’s a reminder that secure traffic (once assumed safe) is not immune from state-level network interference.

In my own network work I’ve seen latency and slowdowns, but a nearly total reset of secure traffic is something you plan for only in worst-case scenarios. The event backs that up.

Impact on users and businesses

Let’s talk impact — both on individuals and on businesses — and why we should care even if you’re not physically in China.

For individual users (inside China or connected to China):

• Users inside China lost access to many foreign websites, cloud services, apps that rely on secure connections outside China.

• Encrypted communication (websites, apps) stalled or failed; even if an app tries repeatedly, it might fail or suffer high latency.

• For someone traveling, or working remotely with Chinese servers, the disruption can look like the internet is misbehaving rather than being censored.

For businesses and enterprises:

• Many enterprise applications use HTTPS (port 443) for connectivity (SaaS tools, VPN tunnels, API calls). The disruption therefore affects business continuity.

• If a multinational company has offices in China or serves customers in China, the outage means that link becomes a single point of failure unless alternative paths exist.

• Cloud providers and global services reliant on cross-border connectivity must account for these risks.

• From a risk management point of view, you must plan for network events that are not just slowdowns but forced resets of secure traffic.

For global internet infrastructure:

• Because China is a major node in the global internet, disruptions there ripple out. If traffic cannot cross the border or if the border is selectively hit, it affects global latency, packet routing, redundancy.

• As a user/service provider outside China, you may not directly see the reason—but you’ll see symptoms: timeouts, connection resets, slower performance, or inability to reach certain IPs.

I recall a project where we had to provide backup connectivity for a service being used in Asia-Pacific, and one of the peering links went down. The experience of scrambling to reroute traffic, adjust configurations, monitor latency, was intense. Now imagine add censorship-induced resets of secure traffic on top of that. It becomes a serious business resilience problem.

Why this matters globally

You might ask: “I’m not in China, why should I care?” Great question. The answer: because the internet is global and secure traffic matters to everyone.

Secure traffic is trust traffic. When you visit your bank website, do a video call, send private data, you rely on encryption (HTTPS). If a major economy like China interferes with secure traffic, it signals that encrypted traffic is not invulnerable. This creates risk.

Cross-border commerce depends on connectivity. Between offices, cloud services, APIs, data transfers – many systems assume “if the network is up, things will work.” But what if the network drops or is reset because of censorship? That assumption fails.

Internet architecture and resilience. The disruption shows that single-points of control or path dependencies matter. If traffic from China is routed in a narrow set of exchange points or under certain devices, it becomes vulnerable. Research shows that internet routing is more centralized than many realize.

Precedents for other countries. China’s approach to internet control is watched by other nations. What happens there might be replicated elsewhere. If you build systems assuming “internet works everywhere”, you may overlook censorship induced disconnects.

In short: even if your business or daily use isn’t China-centric, you should still care about how secure traffic, cross-border links and resilience are evolving. This event is a reminder that infrastructure risk isn’t only about natural disasters or hardware failures — it can be policy-driven, state-driven, protocol-driven.

Mitigation and what can be done

Alright, so given all this, what can you or your organisation do? Here are practical steps (drawn both from what businesses are already doing and from my own experience).

1. Design for redundancy.
If you rely on Chinese connectivity (or serve Chinese users), make sure you have alternate links. That could mean redundant ISPs, peering via different exchange points, routing through other cities or countries. Expect that a critical port (like 443) could be impacted.

2. Monitor connectivity proactively.
Don’t wait for complaints. Use tools to monitor latency, packet loss, failed handshakes, resets (especially on port 443). If you notice unusual behaviours (e.g., many RST packets), your network may be experiencing censorship-driven events.

3. Consider alternative ports/protocols.
If your service must connect with China, you might evaluate using alternative secure ports or protocols (if permissible). For example, if port 443 gets blocked, can you use another port or tunnel? Note: you must stay compliant with local law.

4. Build awareness and response plans.
Include censorship-driven disruptions in your incident response plans. Example: If your SaaS provider reports elevated latency from Chinese nodes, what do you do? How will users fail over? What is your communication strategy?

5. Engage with local compliance and legal counsel.
Because censorship and network policy are often intertwined with regulation, ensure you’re aware of local Chinese internet law, requirements for domestic connectivity, and any reporting obligations for service providers.

6. Review your cloud/SaaS dependencies.
If you use a cloud provider that serves Chinese users or is located in China, review their network architecture: do they route via mainland China? Are they resilient to port 443 resets? Do they provide alternate paths? The blog from Zscaler raised concerns that many links were impacted during the August event.

In my own past work I’ve seen organisations assume “we just run a VPN and all is fine”. But when the VPN endpoint itself is impacted (or the underlying port gets reset), things fall over. So you’ve got to dig deeper than “connectivity = up”.

Looking ahead: future of China’s traffic filtering

What does this kind of event tell us about how the GFW and Chinese censorship infrastructure might evolve? Here are some thoughts, mixing research findings, public reports, and my own take.

Increasing sophistication.
The fact that the device in the August 2025 event didn’t match known fingerprinting means China may be deploying newer or secret devices, or experimenting with new methods. That means the “rules of the game” change faster than many expect.

Targeting encrypted protocols.
In past decades, censorship focused more on HTTP, DNS and non-encrypted traffic. But increasingly encrypted traffic (HTTPS, QUIC, SNI encryption) is targeted. For example, work on QUIC (a newer protocol over UDP) shows China exploring new blocking strategies.

Regional/inside variation.
Research shows that internet censorship inside China doesn’t just come from Beijing’s central system — regional firewalls and provincial filtering are growing. For example in Henan province the number of blocked domains was five times more than the national average.

Business implications.
Companies will need to assume censorship is part of their network risk landscape, especially when China is involved. That means designing more flexibly and being prepared for unexpected disruptions that feel like “network outages” but are really state-driven.

What to watch.

• Watch for incidents targeting ports other than 443 (e.g., QUIC/UDP, alternate secure ports).

• Notice if increased latency or resets happen selectively for certain services rather than blanket.

• Look at routing changes around Chinese exchange points or peering agreements.

• Keep an eye on regulatory changes in China about encryption, TLS/SNI, VPN legality.

From my vantage, these points mean: if you have any service relying on China connectivity, you can’t treat censorship as “someone else’s problem.” It’s part of your architecture now.

Conclusion

The 2025 HTTPS traffic disruption caused by China’s Great Firewall isn’t just a one-off curiosity. It’s a marker for how secure traffic and global connectivity are increasingly at risk of state-level network control.

Here’s what matters most:

• The Great Firewall has always enforced censorship; now it’s showing the capability to disrupt encrypted traffic at scale (i.e., port 443).

• The event on August 20 2025 shows how a targeted reset of secure connections can happen and impact users, businesses, and global networks.

• The technical mechanism (forged TCP RST+ACK packets) highlights how censorship works at the packet level — not just via blocking websites.

• For users and businesses, especially those with China-related connectivity, this means planning for resilience, monitoring potential disruptions, and taking network-risk seriously.

• Even if you’re not dealing with China directly, the incident is a signal: connectivity is not guaranteed simply because you paid for a link. State-level network policy matters.

• Finally, the future points to more nuanced, protocol-level censorship — encrypted traffic, newer protocols (QUIC), alternative ports — meaning you’ll need to stay vigilant.

So if you’re responsible for a service, a network, or an app that touches China or crosses its border in any way, treat this event as a wake-up call. Plan for “what if secure traffic fails”, test failover, monitor resets, and talk to your peers about how they’re doing it.

FAQ

Q: What is the Great Firewall of China?
A: It’s the informal name for China’s combination of laws, regulations and technical systems that monitor, filter or block internet traffic — especially traffic crossing China’s borders or accessing foreign websites.

Q: Why was port 443 (HTTPS) blocked on August 20 2025?
A: According to analysis by monitoring groups, the GFW injected forged TCP RST+ACK packets to interrupt traffic over port 443 for around 74 minutes. The reason is unclear — it may have been a test, mis-configuration or an upgrade in progress.

Q: How can businesses protect themselves against China-based connectivity disruptions?
A: Some strategies: build redundant network paths (not just one link to China), monitor secure traffic for resets/latency, consider alternative ports/protocols (where legal), include censorship risk in your incident planning, review your cloud/SaaS dependencies.

Q: Does this event mean that the internet in China is completely shut down?
A: No. The disruption was temporary (~74 minutes) and targeted at a specific port (443). China’s internet remains highly functional most of the time, but this shows that secure traffic links can be disrupted.

Q: Can users outside of China be affected by the GFW?
A: Yes — if your service depends on Chinese connectivity, or a Chinese user depends on your service, a GFW-driven disruption (or routing issue) can impact you. Also, because routing is often global, cross-border disruptions can ripple outward.