In the F5 XC Distributed Cloud some client information is saved to variables that can be inserted in HTTP headers similar to how F5 Big-IP saves some data that can after that be used in a iRule or Local Traffic Policy. By default XC will insert XFF header with the client IP address but what if the end servers want an HTTP header with another name to contain the real client IP.
Under the HTTP load balancer under "Other Options" under "More Options" the "Header Options" can be found.
Then the the predefined variables can be used for this job like in the example below the $[client_address] is used.
There is $[user] variable and maybe in the future if F5 XC does the authentication of the users this option will be insert the user in a proxy chaining scenario but for now I think that this just manipulates data in the XAU (X-Authenticated-User) HTTP header.
2. Matching of the real client ip HTTP headers
You can also match a XFF header if it is inserted by a proxy device before the F5 XC nodes for security bypass/blocking or for logging in the F5 XC.
For User logging from the XFF Under "Common Security Controls" create a "User Identification Policy". You can also match a regex that matches the ip address and this is in case there are multiple IP addresses in the XFF header as there could have been many Proxy devices in the data path and we want see if just one is present.
For Security bypass or blocking based based on XFF Under "Common Security Controls" create a "Trusted Client Rules" or "Client Blocking Rules". Also if you have "User Identification Policy" then you can just use the "User Identifier" but it can't use regex in this case.
To match a regex value in the header that is just a single IP address, even when the header has many ip addresses, use the regex (1\.1\.1\.1) as an example to mach address 220.127.116.11.
To use the client IP address as a source Ip address to the backend Origin Servers in the TCP packet after going through the F5 XC (similar to removing the SNAT pool or Automap in F5 Big-IP) use the option below:
The same way the XAU (X-Authenticated-User) HTTP header can be used in a proxy chaining topology, when there is a proxy before the F5 XC that has added this header.