Many users find that Hong Kong VPS bandwidth often fails to reach its full potential, even when ISPs advertise 100Mbps, 300Mbps, or even 1Gbps; it frequently only reaches half or even less. This is not uncommon, especially during peak evening hours or when cross-border links are strained. Insufficient bandwidth not only affects website speed but also significantly reduces the efficiency of tasks such as downloading, streaming, and cross-border synchronization, sometimes even raising concerns about server issues. Therefore, systematically analyzing the reasons for insufficient Hong Kong VPS bandwidth is crucial for improving network performance.
In the network architecture of Hong Kong data centers, bandwidth capacity is affected by multiple factors, including the user's local network, the Hong Kong data center's egress point, ISP peering, cross-border links, relay nodes, server configuration, system kernel parameters, and third-party transmission protocol limitations. Different problems require different troubleshooting paths; therefore, a complete diagnostic process must be established, rather than simply concluding that the data center's bandwidth quality is poor based on speed test results. Generally, insufficient Hong Kong VPS bandwidth can be analyzed from three directions: local bottlenecks, server-side bottlenecks, and link bottlenecks.
First, it's necessary to confirm whether there are speed limitations on the local end. For example, if a visitor is located in China and uses their home broadband to test speeds abroad, their local ISP may actively limit international bandwidth, especially mobile broadband. If the local speed test data doesn't even reach the VPS's advertised bandwidth, it's impossible to verify the server's true capabilities. To confirm if the local environment is normal, tests can be conducted using both domestic and overseas speed test nodes. If the speed tests are normal on both local and other VPSs, but only the Hong Kong VPS doesn't reach its full potential, further analysis is necessary.
Secondly, server-side bottlenecks are a concern. Hong Kong VPSs typically use virtualization platforms such as KVM, OpenVZ, and NVMe Cloud. If the server's CPU, network queue, and system kernel parameters are configured low, throughput will be limited. For example, during high-concurrency uploads and downloads, excessive CPU softirq usage can prevent bandwidth from reaching its maximum. If the system frequently displays network queue overflow warnings, such as "net_ratelimit" or "queue full," it indicates insufficient VPS network processing capacity, requiring optimization or a change of server model.
A further crucial check is the Linux network kernel parameters. Hong Kong VPS typically use high-speed gigabit network ports, but the default kernel parameters are not optimized for high-speed transmission, which can easily lead to insufficient TCP buffer and queue depth, thus limiting bandwidth. It is recommended to check the following configurations:
sysctl net.ipv4.tcp_rmem
sysctl net.ipv4.tcp_wmem
sysctl net.core.rmem_max
sysctl net.core.wmem_max
sysctl net.core.netdev_max_backlog
If the buffer parameter is too small, it will directly limit the long-distance transmission speed. The following optimization example can be implemented:
net.core.rmem_max = 67108864
net.core.wmem_max = 67108864
net.core.netdev_max_backlog = 50000
net.ipv4.tcp_rmem = 4096 87380 67108864
net.ipv4.tcp_wmem = 4096 65536 67108864
These optimizations can significantly improve the performance of cross-border high-bandwidth transmission.
A more common reason for Hong Kong VPS bandwidth not being fully utilized is due to link bottlenecks, meaning insufficient capacity in the network path between the data center and the client. Especially in cross-border traffic, the network between Hong Kong and mainland China is not entirely direct; in most cases, it passes through peering points between operators, such as HKT and China Telecom's international segment, CTG and PCCW, HKIX, etc. If these nodes are overloaded during peak hours, bandwidth cannot be fully utilized, and even if the server itself has high outbound bandwidth, users will not be able to achieve full speed.
Diagnosing link bottlenecks usually requires MTR or Traceroute. If the packet loss rate increases significantly at intermediate nodes (especially cross-border nodes), and the time is concentrated between 8 PM and 11 PM, this is typical cross-border congestion, not a VPS failure.
A more detailed approach is to test the download speed from different regions to the server. For example, test nodes from China Mobile, China Unicom, China Telecom, Taiwan, Japan, South Korea, and Singapore. If you can't reach the full speed limit in mainland China, but can in Japan/Singapore, the problem lies in the cross-border segment, not in the data center or the server's local network.
Some Hong Kong VPSs use a "shared bandwidth" model, meaning many users share the same upstream bandwidth pool. When a single user is testing speed, if other users in the pool are consuming a lot of bandwidth, you won't be able to reach the peak speed. This is common with cheaper VPS hosting. If you find your speed fluctuating at certain times of the day, it may be related to congestion in the shared bandwidth pool.
Another easily overlooked situation is bandwidth capping caused by ISP speed limiting protocols. For example, some VPSs have anti-abuse policies enabled; if the system detects prolonged periods of full bandwidth usage, it may automatically trigger soft speed limits. Check your ISP's control panel for bandwidth capping information.
If you still can't reach the full bandwidth limit after testing in multiple locations, try changing the protocol or tools to verify. For example, when testing point-to-point throughput using iperf3, if single-threaded iperf3 fails to reach full capacity, but multi-threaded iperf3 (e.g., -P 4) improves speed, it indicates that the TCP congestion window or link quality is limiting single-connection speed. Many Hong Kong VPSs fail to reach full capacity with single-threaded iperf3 in cross-border connections, but multi-threaded iperf3 can boost speed to near peak, a typical characteristic of cross-border QoS.
If bandwidth is insufficient from your local machine to Hong Kong, try optimizing bandwidth through relays, such as using nodes in Japan or Singapore for forwarding. If relaying allows full capacity while direct connections fail, this further proves that the bottleneck is in the cross-border connection, not the VPS itself.
In summary, insufficient bandwidth on a Hong Kong VPS is not caused by a single issue, but rather by the combined effect of multiple network links. To accurately determine the cause, a step-by-step investigation is necessary, examining the local network, server performance, network kernel, shared bandwidth, cross-border links, and intermediate node load. Different causes require different solutions; blindly changing data centers or service providers often fails to solve the root problem. Only after thoroughly analyzing the network links can you find the most suitable network optimization solution, such as increasing bandwidth specifications, choosing a better ISP, using relay optimization, adjusting TCP parameters, and using multi-threaded downloads.
