UDP checks from our Hohhot node send a packet to the specified port and wait for a reply. The GFW actively filters UDP traffic on specific ports, particularly those associated with VPN protocols such as WireGuard (51820), OpenVPN UDP, and QUIC on non-standard ports. A UDP no-response result from China may indicate the port is closed on the target, the firewall on the target side is dropping it, or the GFW is blocking it before it reaches the destination.

QUIC (UDP port 443) is increasingly filtered at Chinese international gateways. Some carriers — particularly China Telecom on certain routes — drop QUIC packets silently, which degrades performance for HTTP/3-capable services when accessed from inside China. A UDP check on port 443 from our Hohhot node will indicate whether QUIC packets are passing through or being discarded. A failed UDP result with a successful TCP result on the same port confirms QUIC-specific filtering is in place.

For DNS operators or anyone running a public UDP service that needs to be reachable from China, this check is the fastest way to verify reachability from Alibaba Cloud's network in Inner Mongolia. Cross-referencing a UDP result from Hohhot against results from our Hong Kong node is a useful way to determine whether a filtering problem is specific to mainland China infrastructure or affects the broader region.

China's public internet is controlled by three state-owned carriers: China Telecom (AS4134), China Unicom (AS4837), and China Mobile (AS9808). These three operators hold exclusive rights to international gateway capacity, meaning all traffic entering or leaving China passes through their border routers. There is no neutral open IX market comparable to DE-CIX or AMS-IX — domestic peering occurs through state-managed exchange points in Beijing and Shanghai rather than through independent, carrier-neutral facilities.

The Great Firewall (GFW) operates at the international gateway level, filtering and blocking traffic based on IP, SNI, and deep packet inspection. BGP routes announced inside China are not affected by the GFW for domestic paths, but any traffic destined for or arriving from non-Chinese IP space crosses inspection points at each carrier's border. This means latency measurements from inside China to foreign destinations include not only geographic RTT but also any queuing or inspection delay at the border routers.

Our probe node is located in Hohhot, Inner Mongolia, running on Alibaba Cloud infrastructure (AS37963). Hohhot has become one of China's largest data center hubs due to cold climate reducing cooling costs and access to low-cost coal and wind electricity. Alibaba, China Telecom, and China Mobile all operate hyperscale facilities in the region. Hohhot connects to the rest of the Chinese backbone via China Telecom and Unicom long-haul fiber running east toward Beijing and south toward Shanghai.

International latency from China reflects both geography and the GFW border transit. Hohhot to Frankfurt runs approximately 170–195 ms over well-routed paths. Hohhot to London is around 180–200 ms. Hohhot to Los Angeles sits around 130–155 ms, as trans-Pacific cable capacity is better developed than China-Europe terrestrial routes. Within the Asia-Pacific region, Hohhot to Tokyo is approximately 60–80 ms and to Singapore around 90–110 ms. These figures vary by which state carrier handles the international segment.

Results from our Alibaba Cloud node in Hohhot reflect what a server looks like from inside Chinese state carrier infrastructure, specifically through AS37963 which peers with all three national carriers domestically. For sites targeting Chinese users, this is a meaningful test location — it shows whether your server is reachable from inside China, what latency Chinese users experience, and whether the GFW is affecting connectivity to your domain or IP range.