Why proxies can still leak your true ISP / ASN

Quick answer

You route through a residential or SOCKS5 proxy, the site sees a different IP — and yet sophisticated anti-fraud systems still flag you or link the session to your real network. How? The proxy can leak signals about your true ISP or ASN even while masking the IP itself. Here’s how that happens.

IP masked, network exposed

Changing the visible IP is only part of the picture. Anti-fraud systems cross-check many signals, and several can betray the real network behind a proxy: a WebRTC leak revealing your true IP (and thus your real ASN), DNS requests resolving through your real ISP’s servers, an IPv6 path bypassing an IPv4-only proxy, and timing or latency patterns inconsistent with the claimed location. Any of these can expose the network you’re actually on.

The WebRTC and DNS paths

The two biggest culprits are the same that plague VPNs. WebRTC can hand a site your real public IP straight past the proxy — from which your true ISP and ASN are trivially derived. DNS leaks send your lookups via your real ISP’s resolvers, revealing the network even if web traffic goes through the proxy. Confirm both are sealed with our WebRTC Leak Test.

The ASN-mismatch tell

Fraud systems look at consistency. If your visible IP claims to be a residential connection in one country but other signals (timing, a leaked address, DNS) point to a datacenter or a different carrier, the mismatch itself is the red flag. A residential proxy that leaks a datacenter ASN underneath looks exactly like what it is. You can inspect the ASN/network owner of any address with our Bulk IP Audit tool to understand what these systems see.

Why do residential proxies still get caught?

Residential proxies are sold on the promise that their IPs look like real homes — and the IP may. But if the setup leaks your true ASN through any side channel, the trusted-looking residential IP is undermined by the contradictory signal. The proxy’s reputation can also already be flagged if it’s been abused by others sharing it.

Sealing the leaks

Treat a proxy like a VPN for leak purposes: disable or restrict WebRTC (Chrome/Brave/Edge, Firefox), ensure DNS routes through the proxy, handle IPv6, and verify with our WebRTC Leak Test. A proxy is only as private as its leakiest channel.