As I discussed in a previous post, simply redirecting a user to a “friendly” 404 page isn’t the best option. First, the user might not remember what they clicked/typed to get them to the page and also, simply clicking the back button might not be an option, especially if they submitted form data. Fortunately, as F5 LTMs are “Strategic Points of Control,” we can use them to better handle the situation.


First off, let’s determine the desired behavior when a user request induced an error code. In our case, let’s choose 404 as the error code to watch for. If we detect this error code being sent to the user, let’s redirect them to our Home Page ( rather than simply keeping them at an error page. To make their experience better, let’s also hold the user at an custom page for a few seconds while explaining their issue as well as the request that caused the problem.


Since we’re looking for error codes sent by the servers, we’ll need to run our commands from within the “HTTP_RESPONSE” event. As you’ll see from the DevCentral wiki page for HTTP_RESPONSE, there are examples for using the “HTTP::status” command to detect error codes and redirect users. For some, the rule below is perfectly acceptable.



if { [HTTP::status] eq “404” } {

HTTP::redirect “” }



Unfortunately, that rule would result in the user being sent to the redirect page without any explanation as to what they did wrong. So, we’re going to beef the rule up a bit. As you’ll recall from this post, we can set variables from the HTTP_REQUEST event and then reference them from our HTTP_RESPONSE event in order to show the user the link that caused the error.

Here’s a nice sample rule I just whipped up. We’re using “HTTP::respond” so the response comes directly from LTM. Also, I’m setting a variable “delay” to the amount of seconds to keep the user at the hold page.



set hostvar [HTTP::host]

set urivar [HTTP::uri]

set delay 4



if { [HTTP::status] eq “404 } {

HTTP::respond 200 content \ “<html><head><title>Custom Error Page</title></head><body><meta http-equiv=’REFRESH” content=$delay;url=></head>\<p><h2>Unfortunately, your request for $hostvar$urivar casued a 404 error. After 4 seconds, you’ll automatically be redirected to our home page. If you feel you’ve tried a valid link, please contact Sorry for this inconvenience.</h2></p></body></html>” “Content-Type” “text/html”




So, with that rule, the user requests a page that causes a 404 error. LTM will detect the 404 error, and instead of sending it to the user, it will respond with a 200 status code and HTML showing the user the link the requested as well as apologizing and telling them to contact your webmaster if there’s an issue. I was too lazy to use the HTML to make the e-mail address clickable, maybe next time. Also, by using “Meta Refresh,” we’re holding the user at the page for 4 seconds and then sending them to our error page. As you can see, HTTP::respond is a very powerful command. It’s pretty cool being able to use LTM to send HTML to a user.