If you've lost the manual, or acquired a secondhand unit that doesn't have one with it, never fear. Under the Help tab there are links to the PDF and to the Linksys corporate website.
Unfortunately, you're in trouble if you have to call Linksys tech support. On the one occasion that I called them, the first tech I raised couldn't even speak English, and the second was barely competent at it. Both were complete and utter idiots whose response to any nontrivial question was to put me on infinite hold while they went off to query someone else — and then garbled the answer.