Stop Relying on IP-Based Rate Limiting

Rate limiting is essential. It prevents abuse, protects infrastructure, and ensures fair access. But using IP addresses as the key for rate limiting? That’s often a bad move — and it creates more problems than it solves.

The Problem With IP-Based Limits

IP addresses don't represent users. They represent networks. That distinction matters a lot.

In places like universities, corporate offices, shared housing, or even cafes, multiple users often share the same public IP address. If one of those users starts sending too many requests — intentionally or accidentally — everyone behind that IP gets rate-limited or blocked.

This leads to:

• Frustrated users who haven’t done anything wrong
• Support tickets that are hard to debug
• An API that feels unreliable and inconsistent

Even worse, attackers can rotate IPs, use proxies, or blend in with shared IPs, making your IP-based limits mostly ineffective against real threats.

A Better Approach for Public or Unauthenticated Routes

For unauthenticated routes — like login endpoints, registration forms, or open APIs — you still need some kind of protection. But relying purely on IPs is crude.

A better alternative is fingerprinting. Techniques like JA3/JA4 use characteristics of the client’s TLS handshake or network behavior to create a semi-stable identity. It’s not perfect, but it’s significantly harder to spoof or rotate than IPs.

This helps you:

• More accurately distinguish between users
• Reduce collateral damage from shared IPs
• Catch bots and scrapers that try to cycle through IPs

If fingerprinting is off the table, IP-based limits can still act as a fallback, but should be:

• Short-lived (e.g., 10 requests per 10 seconds, not 100/hour)
• Generous enough to avoid punishing normal users
• Combined with other signals (e.g., user agent, behavior patterns)

For Authenticated Routes: Ditch IPs Completely

Once you’ve identified the user — via an account, token, or API key — IP-based limiting should be thrown out.

At that point, you can (and should) use:

• User ID or API key as the rate limit key
• Granular scopes or tiers (e.g., different limits for free vs. paid users)
• Per-endpoint limits (e.g., stricter on sensitive actions)

This gives you way more control, and avoids blocking legitimate traffic just because a few people are on the same network.

Practical Guidelines

Here’s a cleaner breakdown of what works:

• ✅ Use user ID or API key for any authenticated requests
• ✅ Use fingerprinting (JA3/JA4) for unauthenticated routes
• ✅ Combine multiple signals when needed: fingerprint + IP + behavior
• ✅ Keep limits short-term and generous for public endpoints
• ❌ Don’t treat IPs as user identities — they’re not

Final Thoughts

IP-based rate limiting is easy to implement, which is why it’s so common. But in most cases, it’s also lazy and inaccurate. With better tools like fingerprinting and user-based keys available, there’s no good excuse to keep relying on IPs as your primary rate-limiting strategy.