I'm sorry. I'm crossing my realities.
For normal browsing (without the LTM or any iRules) then the case does not matter for what the LTM picks up as [HTTP::host].
When you are processing the [HTTP::host] value through an iRule then the case IS sensitive and needs to be put in a known comparative state, so you should use the "string tolower". I apologize for the mistake and confusion.
when HTTP_REQUEST {
switch -glob [string tolower [HTTP::host]] {
"www.website1.com" { HTTP::respond 301 Location "http://www.google.com" }
"www.website2.com" { HTTP::redirect "http://www.yahoo.com" }
"www.website3.com" { pool website3pool }
}
}