Exam AZ-700 topic 3 question 56 discussion

The X-Forwarded-For client request header field with the client_ip variable (see explanation later in this table) appended to it in the format IP1, IP2, IP3, and so on. If the X-Forwarded-For field isn't in the client request header, the add_x_forwarded_for_proxy variable is equal to the $client_ip variable. This variable is particularly useful when you want to rewrite the X-Forwarded-For header set by Application Gateway so that the header contains only the IP address without the port information. https://learn.microsoft.com/en-us/azure/application-gateway/rewrite-http-headers-url

Agreed: Application Gateway inserts an X-Forwarded-For header into all requests before it forwards the requests to the backend. This header is a comma-separated list of IP ports. There might be scenarios in which the backend servers only need the headers to contain IP addresses. You can use header rewrite to remove the port information from the X-Forwarded-For header. One way to do this is to set the header to the add_x_forwarded_for_proxy server variable. Alternatively, you can also use the variable client_ip