“There’s a certain amount of vulnerability involved with being a network on the Internet. When two networks connect, they have to trust each other—which also means trusting everyone the other one trusts. Internet networks are promiscuous, but their promiscuity is out in the open. It’s free love. Jon Postel, the longtime administrator of the Internet Assigned Numbers Authority, put this into a koan, a golden rule for network engineers: “Be conservative in what you send, be liberal in what you accept.”