Name Based Hosting iRule not working

By the way, if you are using at least 11.4, you may consider using Local Traffic Policies for this:

• SOL15085: Overview of the Local Traffic Policies feature

If you are using a version before 11.4, Traffic Classes can be used:

• SOL7280: Overview of the HTTP Class profile

An example of a Local Traffic Policy to direct queries for www.abc.com to pool1 and www.xyz.com to pool2:

ltm policy policy-hostname-redirect {
    controls { forwarding }
    requires { http }
    rules {
        www.abc.com {
            actions {
                0 {
                    forward
                    select
                    pool pool01
                }
            }
            conditions {
                0 {
                    http-host
                    values { www.abc.com }
                }
            }
            ordinal 1
        }
        www.xyz.com {
            actions {
                0 {
                    forward
                    select
                    pool pool02
                }
            }
            conditions {
                0 {
                    http-host
                    values { www.xyz.com }
                }
            }
            ordinal 2
        }
    }
    strategy first-match
}

Naturally, this can be done via the Web UI, as well.