BIG-IP LTM and ASM - Read xml package to extract information and redirect traffic

in a normal forwarding or proxying scenario, in order to get the XML response, the bigip already made a load balancing decision. You can inspect the traffic and pick up the reference id, the easiest would be to parse the HTTP::payload. Examples here: link text

 

Once you made the decision on where to forward the traffic next, you can chose the node via the "node" commmand and rerun the request through the proxy using the HTTP::retry command. link text

 

An alternative is to use a sideband connection to probe the server and analyze the response before the BigIP makes an LB decision: examples can be found by searching on this site.

 

HTH.

 

If I may add, the XML Content Based Routing feature in LTM can also do this. It's an XML profile and associated iRule. The XPath configuration in the profile can be a little tricky, but once you have it capturing the right value, the iRule is fairly straight forward. here's an example:

when XML_CONTENT_BASED_ROUTING {
    switch $XML_values(0) {
        "12345" {
            pool pool_a
        }
        "67890" {
            pool pool_b
        }
    }
}

As John alludes, depending on when the XML data presents itself in the request, you may have already made a load balancing decision, and/or may need to add some additional persistence tracking if the request is part of a larger session.