Intel 1520 manual Another invalid hostname message to the user

Option	Description (Continued)
Background	Specifies how long DNS entries can remain in the database
timeout	before they are flagged as entries to refresh in the
	background. These entries are still fresh, so they can be
	refreshed after they are served, rather than before. You can
	choose from the following:
	❚ 3 hours
	❚ 6 hours
	❚ 12 hours
	❚ 24 hours
	❚ 48 hours
	For example, the foreground refresh timeout interval is
	24 hours and the background timeout is 12 hours. In this
	situation a user requests an object from my.com and
	16 hours later a user makes a second request for an object
	from my.com. The DNS entry for my.com has not been
	refreshed in the foreground because the entry is not yet
	24 hours old. But since the background timeout has expired,
	the appliance will first serve the user’s request and then
	refresh the entry in the background.
Invalid host	Specifies how long the proxy software should remember that
timeout	a hostname is invalid. This is often called negative DNS
	caching. You can choose from the following:
	❚ Immediate
	❚ 15 minutes
	❚ 30 minutes
	❚ 1 hour
	❚ 1.5 hours
	❚ 2 hours
	For example, if a user specifies an invalid hostname, the
	appliance informs the user that it could not resolve the
	hostname and the appliance gets another request for the
	same hostname. If the appliance still remembers the bad
	hostname, it will not try to look it up again but will simply send
	another invalid hostname message to the user.
Re-DNS on	Enables or disables the appliance’s ability to re-resolve
Reload	hostnames whenever clients reload pages.

46Intel NetStructure Cache Appliance Administrator’s Guide