Understanding "Preferred IP": Why It's Essential for Network Circumvention

In the world of network circumvention—especially for those navigating the complexities of the Great Firewall (GFW)—the term "Preferred IP" (or IP Picking, 优选IP in Chinese) is frequently discussed. It is often touted as a magic bullet for restoring speed and stability to a flagging proxy connection.

But what exactly is a "Preferred IP," and why has it become a cornerstone of modern circumvention technology? This post explores the technical mechanics behind IP picking and its critical role in bypassing network censorship.

The Foundation: Cloudflare and Anycast

To understand "Preferred IP," we must first understand how Content Delivery Networks (CDNs) like Cloudflare operate. Cloudflare uses a technology called Anycast.

In a traditional Unicast network, one IP address belongs to one specific physical server. In an Anycast network, the same IP address is advertised from hundreds of different data centers across the globe. When you send a request to a Cloudflare Anycast IP, the internet's routing protocols (BGP) are supposed to automatically route your traffic to the "closest" data center.

The Problem: When "Closest" Isn't Fastest

For most users, Anycast works perfectly. If you are in New York, you hit a New York node. If you are in London, you hit a London node.

However, for users behind the GFW (Mainland China), the logic of "closest" often breaks down due to:

1. Routing Detours: Due to complex peering agreements and government-imposed routing restrictions, traffic from a Chinese ISP (like China Telecom) might be sent to a Cloudflare node in Los Angeles or even Germany, instead of the geographically closer nodes in Hong Kong, Tokyo, or Seoul.
2. Congested Gateways: The few international gateways exiting China are often heavily congested. Traffic routed through these "bottlenecks" suffers from high packet loss and latency.
3. QoS (Quality of Service) Throttling: The GFW often applies QoS rules to common CDN IP ranges. During peak hours, traffic to certain "popular" Cloudflare IPs may be intentionally slowed down or prioritized lower than other traffic.
4. IP Blocking: The GFW actively blocks thousands of Cloudflare IPs that it identifies as being used for circumvention.

What is "Preferred IP" (IP Picking)?

Preferred IP is the process of manually scanning thousands of IP addresses within a CDN's (usually Cloudflare's) massive pool to find specific IPs that:

• Are not blocked by the firewall.
• Have a direct routing path from your specific ISP to a high-performance node (e.g., finding a node that routes through the CN2 GIA or a direct peer to Hong Kong).
• Exhibit low latency and zero packet loss during peak hours.

Instead of letting the network decide which IP you connect to, you use tools to "pick" the ones that perform best for your specific local network environment.

Why Apply This to Circumvention Servers?

When you set up a circumvention tool (like Xray, V2Ray, or Trojan) using a CDN-based architecture (e.g., WebSocket + TLS + CDN), your traffic follows this path:

User → Cloudflare Edge (IP) → Your VPS (Origin Server)

The weak link in this chain is often the first hop: User → Cloudflare Edge. If the IP address your client connects to is throttled or poorly routed, your entire connection will be slow, regardless of how fast your VPS is.

1. Drastic Reduction in Latency

By "picking" an IP that routes to a nearby data center (like San Jose for China Unicom or Hong Kong/Japan for certain high-end routes), users can often drop their latency from 300ms+ down to sub-100ms.

2. Bypassing QoS Throttling

Firewalls often throttle traffic to the most commonly assigned "default" IPs. By finding a "Preferred IP" that is less commonly used by the general public, you can often bypass these specific throttling rules and achieve much higher throughput.

3. Stability During Peak Hours

Network congestion usually hits its peak in the evenings. An IP that works fine at 10:00 AM might be unusable at 9:00 PM. IP picking allows users to find "robust" IPs that maintain performance even when the international gateways are under heavy load.

4. Resilience Against IP Bans

If the GFW blocks a specific Cloudflare IP, your connection breaks. IP picking allows you to quickly swap out the blocked IP for a fresh, working one without needing to change your VPS settings or your domain configuration.

How is it Done?

The most common way to find a Preferred IP is by using open-source scanning tools like CloudflareSpeedTest. These tools perform the following steps:

1. Download a list of all known Cloudflare IP ranges.
2. Ping thousands of IPs to check for basic reachability and latency.
3. Perform a speed test (downloading a small file) on the fastest candidates to measure actual throughput.
4. Output a list of the top-performing IPs.

Once found, these IPs are either entered manually into the circumvention client (e.g., v2rayNG, Clash) or used in conjunction with a custom "Host" header or a "Fake DNS" setup.

Conclusion

"Preferred IP" is more than just a performance tweak; for many, it is the difference between a usable internet and a broken one. By understanding how Anycast works and how regional routing issues can be exploited or bypassed, users can turn a sluggish, unreliable proxy into a high-speed, stable bridge to the global web.

While the "cat and mouse" game between censors and users continues, IP picking remains one of the most effective tools in the user's arsenal for reclaiming network performance.