ACK

In data networking, an acknowledgement (or acknowledgment) is a signal passed between communicating processes or computers to signify acknowledgement, or receipt of response, as part of a communications protocol. For instance, ACK packets are used in the Transmission Control Protocol (TCP) to acknowledge the receipt of SYN packets when establishing a connection, data packets while a connection is being used, and FIN packets when terminating a connection.

Checksum

A checksum is a small-sized datum from a block of digital data for the purpose of detecting errors which may have been introduced during its transmission or storage. It is usually applied to an installation file after it is received from the download server. By themselves, checksums are often used to verify data integrity but are not relied upon to verify data authenticity.

Classless Inter-Domain Routing (CIDR)

Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and routing Internet Protocol packets. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous addressing architecture of classful network design in the Internet. Its goal was to slow the growth of routing tables on routers across the Internet, and to help slow the rapid exhaustion of IPv4 addresses.

CIDR notation is a syntax for specifying IP addresses and their associated routing prefix. It appends a slash character to the address and the decimal number of leading bits of the routing prefix, e.g., 192.168.2.0/24 for IPv4, and 2001:db8::/32 for IPv6.

Default Gateway

A default gateway in computer networking is the node that is assumed to know how to forward packets on to other networks. Typically in a TCP/IP network, nodes such as servers, workstations and network devices each have a defined default route setting, (pointing to the default gateway), defining where to send packets for IP addresses for which they can determine no specific route. The gateway is by definition a router.

Encapsulation (networking)

In computer networking, encapsulation is a method of designing modular communication protocols in which logically separate functions in the network are abstracted from their underlying structures by inclusion or information hiding within higher level objects.

Loopback Interface

The Internet Protocol (IP) specifies a loopback network with the (IPv4) address 127.0.0.0/8. Most IP implementations support a loopback interface (lo0) to represent the loopback facility. The most commonly used loopback IP address is 127.0.0.1 for IPv4 and ::1 for IPv6.

Maximum Transmission Unit (MTU)

A maximum transmission unit (MTU) is the largest size packet or frame, specified in octets (eight-bit bytes), that can be sent in a packet- or frame-based network such as the Internet. The Internet's Transmission Control Protocol (TCP) uses the MTU to determine the maximum size of each packet in any transmission.

For example, over Ethernet TCP MTU is 1500 bytes.

Network Address Translation (NAT)

Network Address Translation (NAT) is a method of remapping one IP address space into another by modifying network address information in Internet Protocol (IP) datagram packet headers while they are in transit across a traffic routing device.

Neighbor Discovery Protocol (NDP)

The Neighbor Discovery Protocol (NDP) is a protocol in the Internet protocol suite used with Internet Protocol Version 6 (IPv6). It operates in the Link Layer of the Internet model (RFC 1122) and is responsible for address autoconfiguration of nodes, discovery of other nodes on the link, determining the link layer addresses of other nodes, duplicate address detection, finding available routers and Domain Name System (DNS) servers, address prefix discovery, and maintaining reachability information about the paths to other active neighbor nodes (RFC 4861).

Node

In communication networks, a node (Latin nodus, ‘knot’) is either a redistribution point (e.g. data communications equipment), or a communication endpoint (e.g. data terminal equipment). The definition of a node depends on the network and protocol layer referred to. A physical network node is an active electronic device that is attached to a network, and is capable of creating, receiving, or transmitting information over a communications channel.

Port Forwarding

Port forwarding is the process of forwarding requests for a specific port to another host, network, or port. As this process modifies the destination of the packet in-flight, it is considered a type of NAT operation.

Reverse Proxy

In computer networks, a reverse proxy is a type of proxy server that retrieves resources on behalf of a client from one or more servers. These resources are then returned to the client as though they originated from the proxy server itself.

Subnet

A subnetwork, or subnet, is a logical, visible subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting.

The routing prefix is expressed in CIDR notation (Classless Inter-Domain Routing notation). It is written as the first address of a network, followed by a slash character (/), and ending with the bit-length of the prefix. For example, 192.168.1.0/24 is the prefix of the Internet Protocol Version 4 network starting at the given address, having 24 bits allocated for the network prefix, and the remaining 8 bits reserved for host addressing.