Technology - IP Techniques 2 - Network Address Translation

Synopsis

Network Address Translation (NAT) firewalls are ubiquitous in residential and most commercial Internet connections, but are necessary due to the shortage of IPv4 address space. This report discusses the operation of NAT firewalls, the problems they create by preventing any-to-any connectivity, and NAT traversal techniques including STUN, (Simple Traversal of UDP over NAT), TURN (Traversal Using Relay NAT) and ICE (Interactive Connectivity Establishment).

Table of Contents

• 1. Synopsis
• 2. Introduction
• 3. Implementation and lack of standards
  • 3.1 Deployment in ADSL and HFC cable modems
  • 3.2 BEHAVE
  • 3.3 NAT discouraged for IPv6
  • 3.4 NAT for security
  • 3.5 Multiple hosts behind one IP address
• 4. Operation with TCP
  • 4.1 Example of NAT handling a TCP session
    • 4.1.1 Establishing the session
    • 4.1.2 Address translation
    • 4.1.3 Translating the TCP port number
  • 4.2 NAT typically precludes running local servers
  • 4.3 TCP is easily handled by NAT
• 5. UDP packets and NAT
  • 5.1 Multicast streaming media and NAT
  • 5.2 Deep packet inspection
• 6. NAT breaks fundamental requirements for Internet communications
  • 6.1 Difficulties with Application Level Gateways
  • 6.2 The pressure for NAT adoption
• 7. NAT Traversal Techniques
  • 7.1 Universal Plug and Play
  • 7.2 Middlebox Communications (MIDCOM)
  • 7.3 Simple Traversal of UDP over NAT (STUN)
    • 7.3.1 Simple Traversal Underneath NAT (STUN-bis)
    • 7.3.2 Types of NAT firewall
    • 7.3.3 STUN operation
  • 7.4 Traversal Using Relay NAT (TURN)
  • 7.5 Interactive Connectivity Establishment (ICE)
• 8. Related reports