8. New transport-layer protocols will work across the Internet
IP was designed to support new transport protocols underneath it, but increasingly this isn't true, Thaler says. Most NATs and firewalls only allow Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) for transporting packets. Newer Web-based applications only operate over Hypertext Transfer Protocol (HTTP).
9. If one stream between you and me can get through, so can another one
Some applications open multiple connections -- one for data and another for control -- between two systems for communications. The problem is that middle-boxes such as NATs and firewalls block certain ports and may not allow more than one connection. That's why applications such as File Transfer Protocol (FTP) and the Real-time Transfer Protocol (RTP) don't always work, Thaler says.
10. Internet communications are not changed in transit
Thaler cites several assumptions about Internet security that are no longer true. One of them is that packets are unmodified in transit. While it may have been true at the dawn of the Internet, this assumption is no longer true because of NATs, firewalls, intrusion-detection systems and many other middle-boxes. IPsec solves this problem by encrypting IP packets, but this security scheme isn't widely used across the Internet.
11. Internet communications are private
Another security-related assumption Internet developers and users often make is that packets are private. Thaler says this was never true. The only way for Internet users to be sure that their communications are private is to deploy IPsec, which is a suite of protocols for securing IP communications by authenticating and encrypting IP packets.
12. Source addresses are not forged
Many Internet applications assume that a packet is coming from the IP source address that it uses. However, IP address spoofing has become common as a way of concealing the identity of the sender in denial of service and other attacks. Applications built on this assumption are vulnerable to attack, Thaler says.