When using squid,
HTTP_VIA=1.1 sheldows-vista:80 (squid/2.7.STABLE4)
HTTP_X_FORWARDED_FOR=96.48.192.227
LOCAL_ADDR=127.0.0.1
REMOTE_ADDR=127.0.0.1
REMOTE_HOST=127.0.0.1
HTTP_X_FORWARDED_FOR is the ip address of the client connected to the proxy, or if squid made a request for multiple clients, then sometime X-FORWARDED-FOR may contain multiple ip addresses seperated by "," such as:
HTTP_X_FORWARDED_FOR = x.x.x.x,y.y.y.y, z.z.z.z
REMOTE_ADDR will be the ip address of the proxy
REMOTE_HOST will be either the ip address of the proxy or the name of the proxy machine