Understanding IRules and Syntax

when LTM receive a HTTP Request, do the following code

when HTTP_REQUEST {

execute the command HTTP::header exists "x-forwarded-for"

Inserting this command between brackets allow to retreive the result of the command.

the command [HTTP::header exists "x-forwarded-for"] will return 0 if doesn't exist (for false), 1 if exist (for true)

Then [string tolower [HTTP::header exists "x-forwarded-for"]] convert the result of command to lowercase... doesn't make sense because lowercase of a number stay the same...

and finally, if the result is a number different than 0, execute the code between curly brackets

if { [string tolower [HTTP::header exists "x-forwarded-for"]] } {

log in /var/log/ltm the line XFF_HEADER=W.X.Y.Z where W.X.Y.Z is the value of HTTP header X-Forwarded-For

log local0. "XFF_HEADER=[HTTP::header values "X-Forwarded-For"] " } }