Normally Squid tries to use parents for most requests. If you for some
	reason like it to first try going direct and only use a parent if
	going direct fails set this to on.

	By combining nonhierarchical_direct off and prefer_direct on you
	can set up Squid to use a parent as a backup path if going direct
	fails.

	Note: If you want Squid to use parents for all requests see
	the never_direct directive. prefer_direct only modifies how Squid
	acts on cacheable requests.