A10 — X-forwarded-for

If your A10 is configured to append the client IP (the default), the header becomes: X-Forwarded-For: 127.0.0.1, 203.0.113.5

X-Forwarded-For: <client>, <proxy1>, <proxy2>

If a backend server receives requests from multiple clients over the same persistent connection from the A10, the XFF header will change per request . Your backend application code must be designed to parse the XFF header on every HTTP request, not just at the TCP connection establishment. Java HttpServletRequest.getRemoteAddr() will still return the A10’s IP; you must explicitly call getHeader("X-Forwarded-For") . Blindly trusting the first XFF value you see is a common and dangerous anti-pattern.

When a client connects to an A10 VIP (Virtual IP), the A10 establishes a separate TCP connection to the backend server. From the server’s perspective, the source IP of every single packet is the A10’s own LAN IP—not the remote user. This breaks logging, geo-location, rate-limiting, and security rules.

A10 provides a configuration option to prevent this. Instead of appending, you can configure the ADC to or replace the XFF header.

A malicious client sends an HTTP request directly to your A10 with a forged header: GET /admin HTTP/1.1 X-Forwarded-For: 127.0.0.1