HTTP requests and responses often include header fields that provide contextual information about the message. RFC 2616 defines a standard set of HTTP header fields. Some non-standard header fields, which begin with X-, are common.The Load Balancing service adds or modifies the following X-headers when it passes requests to your servers.
The Host header is an HTTP header needed when multiple sites share a single IP address. See also http-headers. SQL Injection through HTTP Headers - Infosec Resources Mar 30, 2012 Spoof HTTP Headers Using Squid Proxy Server - Jajo
General headers and entity headers are the same for both the server and client. All headers in HTTP messages contain the header name followed by a colon (:), then a space, and the value of the header. Header names are case-insensitive (thus, Content-Type is the same as Content-type). The value of a header can extend over multiple lines by The Host request header specifies the host and port number of the server to which the request is being sent. If no port is included, the default port for the service requested (e.g., 443 for an HTTPS URL, and 80 for an HTTP URL) is implied. A Host header field must be sent in all HTTP/1.1 request
The Host property can be used to set the Host header value to use in an HTTP request independent from the request URI. The Host property can consist of a hostname and an optional port number. A Host header without port information implies the default port for the service requested (port 80 for an HTTP URL, for example).
AskF5 | Manual Chapter: HTTP Profiles You can insert headers into HTTP requests. The HTTP header being inserted can include a client IP address. Including a client IP address in an HTTP header is useful when a connection goes through a secure network address translation (SNAT) and you need to preserve the original client IP address.