# Special Purpose Environment Variables

Interoperability problems have led to the introduction of mechanisms to modify the way Apache behaves when talking to particular clients. To make these mechanisms as flexible as possible, they are invoked by defining environment variables, typically with BrowserMatch, though SetEnv and PassEnv could also be used, for example.

## downgrade-1.0

This forces the request to be treated as a HTTP/1.0 request even if it was in a later dialect.

## force-no-vary

This causes any `Vary` fields to be removed from the response header before it is sent back to the client. Some clients don't interpret this field correctly (see the known client problems page); setting this variable can work around this problem. Setting this variable also implies force-response-1.0.

## force-response-1.0

This forces an HTTP/1.0 response when set. It was originally implemented as a result of a problem with AOL's proxies. Some clients may not behave correctly when given an HTTP/1.1 response, and this can be used to interoperate with them.

## nokeepalive

This disables KeepAlive when set. Because of problems with Netscape 2.x and KeepAlive, we recommend the following directive be used:

        BrowserMatch Mozilla/2 nokeepalive