Hole punching is a computer networking technique for establishing communications between two parties in separate organizations who are both behind restrictive firewalls. Used for applications such as online gaming, P2P

Peer-to-peer

Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...

 and VoIP

Voice over IP

Voice over Internet Protocol is a family of technologies, methodologies, communication protocols, and transmission techniques for the delivery of voice communications and multimedia sessions over Internet Protocol networks, such as the Internet...

, both clients establish a connection with an unrestricted third-party server that uncovers external and internal address information for them. Since each client initiated the request to the server, the server knows their IP addresses and port numbers assigned for that session, which it shares one to the other. Having valid port numbers causes the firewalls to accept the incoming packets from each side. ICMP hole punching

ICMP hole punching

ICMP hole punching is a technique employed in network address translator applications for maintaining Internet Control Message Protocol packet streams that traverse the NAT...

, UDP hole punching

UDP hole punching

UDP hole punching is a commonly used technique employed in network address translator applications for maintaining User Datagram Protocol packet streams that traverse the NAT...

 and TCP hole punching

TCP hole punching

TCP hole punching is a commonly-used NAT traversal technique, for sending 2-way messages between nodes in an Internet computer network. The term "NAT traversal" is a general term for techniques that establish and maintain TCP/IP network and/or TCP connections traversing network-address-translation ...

 respectively use Internet Control Message

Internet Control Message Protocol

The Internet Control Message Protocol is one of the core protocols of the Internet Protocol Suite. It is chiefly used by the operating systems of networked computers to send error messages indicating, for example, that a requested service is not available or that a host or router could not be...

, User Datagram

User Datagram Protocol

The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...

 and Transmission Control Protocol

Transmission Control Protocol

The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...

s.

See also

• Firewall pinhole
  Firewall pinhole
  In computer networking, the term firewall pinhole is used to describe a port that is opened through a firewall to allow a particular application to gain controlled access to the protected network....
  
  
• Hamachi - software example
• ICMP hole punching
  ICMP hole punching
  ICMP hole punching is a technique employed in network address translator applications for maintaining Internet Control Message Protocol packet streams that traverse the NAT...
  
  
• UDP hole punching
  UDP hole punching
  UDP hole punching is a commonly used technique employed in network address translator applications for maintaining User Datagram Protocol packet streams that traverse the NAT...
  
  
• TCP hole punching
  TCP hole punching
  TCP hole punching is a commonly-used NAT traversal technique, for sending 2-way messages between nodes in an Internet computer network. The term "NAT traversal" is a general term for techniques that establish and maintain TCP/IP network and/or TCP connections traversing network-address-translation ...
  
  
• Universal Plug and Play
  Universal Plug and Play
  Universal Plug and Play is a set of networking protocols for primarily residential networks without enterprise class devices that permits networked devices, such as personal computers, printers, Internet gateways, Wi-Fi access points and mobile devices to seamlessly discover each other's presence...