--- title: "Proxy detection API: trusted IPs, IPv6 and integration" description: "Integrate a proxy detection API with trusted client IPs, IPv6 handling and missing results. Distinguish Tor, relays and proxy labels before taking action." status: published author: Michael Delgado datePublished: 2026-10-21 dateModified: 2026-10-21 --- # Proxy detection API: trusted IPs, IPv6 and integration *By Michael Delgado · Published 2026-10-21 · Last updated October 21, 2026.* A proxy detection API assesses a network address or connection using the service’s defined categories and evidence. A reliable integration starts by identifying the correct client address, preserving the IP family and attaching the result to the protected event. Unknown, failed and unsupported results should remain separate from an evaluated negative finding. ## Establish the trusted client-IP boundary A website behind a CDN or reverse proxy can receive several addresses and forwarding headers. Identify which component is trusted to supply the original client context and prevent arbitrary public requests from setting that field as authoritative. [Cloudflare’s HTTP header reference](https://developers.cloudflare.com/fundamentals/reference/http-headers/) documents its forwarding fields and related configuration. Use the contract for your actual deployment. Do not copy a header name from an example and trust it at every unrelated network boundary. Record the address used for the assessment and the relevant event reference under your data practices. This makes it possible to investigate whether a surprising result came from the detector or from incorrect attribution. ## Keep IPv4 and IPv6 behavior explicit Confirm supported IP families, address parsing and any network-layer transformations. An address representation chosen by another component should not silently change which endpoint the API evaluates. Ask what happens when a client address is unavailable or unsupported. The application needs a visible state for that result rather than silently substituting the origin server’s address or an unrelated default. | Input or result state | What to preserve | Response to define | | --- | --- | --- | | Valid supported address | IP family, event and observation time | Apply the documented policy | | Unavailable client context | The attribution failure | Retry or use an alternate path | | Unsupported input | The parsing or service limit | Avoid a misleading clean result | | Unknown classification | The provider’s stated uncertainty | Review according to the action | | API unavailable | Failure reference and timing | Use the chosen fallback | ## Distinguish Tor, privacy relays and generic proxies Request the definition of each returned field. A Tor-related observation, a hosting-network classification and a privacy-relay category do not all describe the same claim. A numeric score may combine observations in a provider-specific way. [Apple’s Private Relay guidance](https://developer.apple.com/icloud/prepare-your-network-for-icloud-private-relay/) includes information for networks and web servers that encounter that service. Verify the current official publication if your policy needs to recognize its ranges. Do not turn an old copied list into an indefinite account identity. The [VPN and proxy buyer guide](/blog/vpn-proxy-detection-tools/) covers provider selection. The [IP fraud-score article](/blog/ip-fraud-score/) explains why thresholds and score direction must come from the chosen service’s documentation. ## Bind the assessment to the business event Keep the network assessment, authenticated account if one exists, action reference and decision time together. A later lookup can provide different context from the result available when the original action was evaluated. For a hypothetical payment flow, inspect when the network assessment arrives relative to the order decision. Define whether a delayed result can still affect the action, whether it creates a review case or whether it is retained only as later evidence. Do not allow a late callback to create a duplicate business operation. The [fraud API guide](/blog/fraud-detection-api/) covers server credentials, integrity and safe retries for the wider integration. ## Scope caching and retries carefully Use the provider’s documented caching and update contract. A cached assessment can reduce repeated requests, but the business should know what event and observation time it represents. Avoid treating it as a permanent verdict on a customer. Separate retrying an assessment from retrying the protected operation. The first may return another result; the second must not accidentally grant another benefit or submit another payment. Keep the business-action identifier stable. Monitor request volume by journey. Repeated collection loops and integration retries can produce a usage spike that looks like new traffic. Check those causes before reporting an attack or changing the purchased allowance. ## Apply proportionate action and review Use network evidence with account history, authentication and the protected rule. Legitimate customers can use relays, shared networks and mobile connections. The [residential-proxy guide](/blog/residential-proxy-detection/) explains how to test those cases. Keep a correction owner and a safe fallback for an API outage. Support should be able to distinguish an unavailable assessment from a customer restriction based on reviewed evidence. That distinction matters more than a clean-looking dashboard full of default scores. ## FAQ ### Can I trust any X-Forwarded-For header? Only within the trusted forwarding contract of your deployment. A public caller must not be able to choose the authoritative client address arbitrarily. ### Should IPv6 be converted into an unrelated default IPv4 address? Do not silently substitute another endpoint. Follow the actual network and service contract and preserve unsupported or missing states. ### Does a Tor or proxy result identify a person? No. It contributes network context to an event. Account identity and authorization require their own evidence. ## Sources - [Cloudflare: HTTP headers](https://developers.cloudflare.com/fundamentals/reference/http-headers/). - [Apple: Private Relay network and server guidance](https://developer.apple.com/icloud/prepare-your-network-for-icloud-private-relay/). - [OWASP: REST security](https://cheatsheetseries.owasp.org/cheatsheets/REST_Security_Cheat_Sheet.html).