Residential vs. Datacenter vs. Mobile Proxies:
A Defender's Guide

Not all IP addresses are created equal. When your server receives a request, the IP address tells a story about where that request came from. But in the world of fraud and abuse, that story is often a lie fabricated by a proxy.

To defend your application effectively, you need to understand the three main categories of proxies used by attackers: Datacenter, Residential, and Mobile.

1. Datacenter Proxies

What they are: IPs owned by cloud hosting providers like AWS, DigitalOcean, or obscure hosting companies. They physically reside in a server rack in a data center.

The Threat: Speed and volume. Attackers use these for high-volume brute force attacks, credential stuffing, or basic scraping. They are cheap and fast.

Defense: This is the "easy mode" of defense. Since real human users almost never browse from a datacenter IP, you can safely block or challenge traffic from these ASNs (Autonomous System Numbers).

2. Residential Proxies

What they are: IP addresses assigned by ISPs (Internet Service Providers) like Comcast, AT&T, or Verizon to actual homeowners. These IPs serve real families.

How attackers get them: Unknowing users install free VPNs, browser extensions, or infected apps that turn their device into a proxy node. The attacker routes traffic through Grandma's iPad in Ohio.

The Threat: Evasion. Because the request looks like it's coming from a legitimate user, traditional "blacklists" fail here. You can't block the IP permanently because tomorrow it belongs to a valid customer.

Defense: This is where it gets hard. You cannot rely on static lists. You need strictly real-time intelligence to catch when an IP is currently being used as a proxy exit node.

3. Mobile Proxies (4G/5G)

What they are: IPs assigned to mobile devices on cellular networks.

The "CGNAT" Problem: Mobile carriers use Carrier-Grade NAT (CGNAT). This means thousands of distinct mobile users might share the same public IP address simultaneously.

The Threat: Account Takeover and targeted scraping. Attackers love mobile proxies because you are terrified to block them. If you blacklist a T-Mobile IP, you might accidentally block 5,000 legitimate iPhone users in Downtown Los Angeles.

Defense: Blocking is rarely an option. You must rely on browser fingerprinting, behavioral analysis, and specialized IP reputation scores that understand CGNAT dynamics.

Why Traditional Blacklists Fail

The old way of "downloading a blacklist once a week" is dead.

• Stale Data: Residential IPs rotate constantly. A list from Monday is useless by Wednesday.
• Collateral Damage: Blocking a shared mobile IP kills revenue.

The Solution: You need an API that determines IP reputation in milliseconds, answering the question: "Is this specific IP acting like a proxy right now?"

That is exactly what we built at IPASIS.