iRule – Altering Header Information

This iRULE example will alter the incoming URI before passing the request to the servers:

when HTTP_REQUEST { switch -glob [HTTP::uri] { /old_URI/* { HTTP::uri /new_URI[HTTP::uri] } } }

In this case, for any incoming request that starts with the URI “/old_URI/” (, the “/old_URI/” will be replaced with “/new_URI/old_URI” and this will be passed to the servers (

The various interpretations within the switch statement:

/old_URI/      – URI equals /old_URI/
/old_URI/*    – URI starts with /old_URI/
*/old_URI/* – URI contains /old_URI/

Instead of the “switch” statement, we can also use an “if-statement” like this:

when HTTP_REQUEST { if { [HTTP::uri] starts_with "/old_URI/" } { HTTP::uri /new_URI[HTTP::uri] } }

A slightly more complex version of the URI function alteration is provided here:

when HTTP_REQUEST { set HOST [string tolower [HTTP::host]] set URI [string tolower [HTTP::uri]] if { $URI contains "/NEW_Session_ID=" } {HTTP::uri [string map {/NEW_Session_ID= /OLD_Session_ID=} [HTTP::uri]] pool POOL-WEB-Server } } when HTTP_RESPONSE { if { [HTTP::header values Location] contains "/OLD_Session_ID=" } { HTTP::header replace Location [string map {/OLD_Session_ID= /NEW_Session_ID=} [HTTP::header value Location]] } }

For any incoming HTTP Request, “/NEW_Session_ID=” within the URI is replaced with “/OLD_Session_ID=” and passed to the servers in the pool “POOL-WEB-Server”.

For any HTTP Response from the server to the client that contains the HTTP Header Location, “/OLD_Session_ID=” is replaced with “/NEW_Session_ID=”

This can be used to “mask” the URI or any other header information between the client and the server.

The following iRule will remove “/m/” in the incoming URI and send a redirect:

set URI [string tolower [HTTP::uri]]
if {$URI starts_with "/m/" }{ 
set NEW_URI [string map {"/m/" "/"} [HTTP::uri]] 
HTTP::respond 301 Location "$NEW_URI"


$ curl -I
HTTP/1.0 301 Moved Permanently
Server: BigIP
Connection: Keep-Alive
Content-Length: 0

The “/m/” in the URI is replaced with “/” as seen in the “Location” header.

This has been tested in production environment on 10.x code of F5 LTM

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