ClientIP

ClientIP refers to the IP address of the client that initiated a network connection or request as observed by a server. In simple deployments, ClientIP is the source address of the TCP connection. In modern architectures that sit behind proxies, load balancers, or content delivery networks, the value presented to the backend may come from headers inserted by those intermediaries, rather than the actual end user.

In practice, ClientIP is used for logging, access control, rate limiting, and geolocation. It helps servers distinguish requests from different clients, enforce security policies, and tailor responses based on location. However, it relies on trust in the network path: if proxies are not trusted, or headers are spoofed, the reported ClientIP may be incorrect or misleading.

Common methods to determine the true client address include inspecting headers such as X-Forwarded-For, X-Real-IP, and the Forwarded header (RFC 7239), in combination with a trusted-proxy configuration. When using these headers, software should only trust them from known, secure proxies and avoid treating untrusted headers as definitive. Backends may preserve a chain of IPs to show the path a request took, but this adds complexity.

Limitations include the presence of NAT, CGNAT, VPNs, shared proxies, and dynamic IPs, all of which can obscure the actual client. Privacy considerations are also important, as IP addresses can be personal data under various regulations; data collection should follow data minimization and relevant legal requirements.