Intel 1520 manual Option Description

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The following table describes the options:

Option	Description
Lookup Timeout	Specifies the timeout period in seconds for the IP address
	lookup operation in the host database.
Foreground	Specifies how long DNS entries can remain in the
Timeout	database before they are flagged as stale. For example, if
	foreground timeout is 24 hours, and a user requests an
	entry that has been in the database for 24 hours or longer,
	the entry is refreshed before being served.
	You can set the background timeout (see next item) to
	refresh entries in the background, before objects become
	stale.
	Be careful that you don’t set the foreground timeout too
	low as you might slow response time. Also, setting this
	time too high risks accumulation of incorrect information.
	Setting the foreground timeout to greater than or equal to
	the background timeout disables background refresh.
Background	Specifies how long DNS entries can remain in the
Timeout	database 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.
	For example, suppose the foreground timeout is 24 hours
	and the background timeout is 12 hours. 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, then refresh the entry in the
	background.
Invalid Host	Specifies how long the proxy software should remember
Timeout	that a host name is invalid. This is often called negative
	DNS caching.
	For example, if a user specifies an invalid host name, the
	appliance informs the user that it could not resolve the
	name, and the appliance gets another request for the
	same host name. If the appliance still remembers the bad
	name, it won’t try to look it up again, but will send another
	“invalid host name” message to the user.
Re-DNS On	Re-resolves host names whenever clients reload pages.
Reload

Chapter 5 Using the Command-Line Interface 97