The Number One Answer: A Sit-Down VPN
The answer that helps administrators sleep most securely is a fixed Virtual Private Network (VPN). A VPN uses end-to-end encryption to carve out a private tunnel over the public network.
The most secure VPN is the traditional arrangement with the telecommuter coming from a fixed site, ideally using a managed, corporate device, and terminating in a secure, private network on either side. Quite a bit of effort can go into setting up this arrangement; you need to see that hardware, software, and settings, as well as authentication, are set up perfectly and maintained on both ends, despite user changes to software, firmware, and hardware, but the security can be worth the trouble.
Don't let this next bit scare you away: After the act with all the acronyms, you'll have the secret of the monster sneaking past the alarms, and everything lightens up.
Let's throw out some protocols -- literally. There are three or four at this end of the pool. Only one from this group is secure enough to take seriously: IPSec, especially in conjunction with L2TP.
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