Wildcard for Host Subdomains inside a Switch?

Thanks for the advice - I will give that a try!

Just to check I understand, are the "log.local0." entries just so I can check the logic is working in the LTM log?

So, if all looks good on testing, the actual rule would look something like this?

when HTTP_REQUEST {
    switch -regexp [string tolower [HTTP::host]] {
        .*\.a.com {
            do something
         }
        .*\.b.com {
            do something
         }
        default {
            do something
        }
}

Thanks again!