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| This glossary uses network terms from the OSI model. Click on one of the categories on the left or on the image below. Click the View All link to see all terms. Use the alphabet to jump to that letter. Some of the terms could be used on multiple layers, but they are grouped in the most common layer. |
Network
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C
Circuit-switched network |
| A telephony or wide area network (WAN) link that provides a temporary connection over a dedicated pathway through the service provider’s network core. (Network Layer) Top |
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G
Gateway |
| A classic term for a router; a router at the edge of a network or enterprise internet; a multi-layer protocol converter. Before the term router was settled upon, routers were called gateways, which is the source of the still common term “default gateway,” meaning the default router on a subnetwork, used by local hosts when transmitting packets to remote networks not found in their own routing tables. The term gateway eventually came to refer to a system capable of translating each layer of all or a portion of the protocol stack of inbound data to protocols in the corresponding layers of a different stack before transmitting the data out through a different interface. (Network Layer) Top |
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H
Host |
| A networked device with an IP address; a mainframe computer system; the operating system on which a hypervisor runs. IP hosts are named after the mainframes of legacy and modern centralized networking environments. (Network Layer) Top |
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I
ICMP |
| Stands for "Internet Control Message Protocol." When information is transferred over the Internet, computer systems send and receive data using the TCP/IP protocol. If there is a problem with the connection, error and status messages regarding the connection are sent using ICMP, which is part of the Internet protocol. (Network Layer) Top |
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IGMP |
| nternet Group Management Protocol (IGMP; Defined in RFC 1112) is a protocol that allows a host to advertise its multicast group membership to neighboring switches and routers. IGMP is a standard protocol used by the TCP/IP protocol suite to achieve dynamic multicasting. (Network Layer) Top |
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Internetwork |
| A network of networks. An internetwork, or internet for short, is created when two or more autonomous networks are interconnected, usually with one or more Layer-3 devices in between. For instance, two fully established LANs connected to one another by a single router constitutes a simple internet. The “internet” refers to the global internetwork that exists by virtue of autonomous networks from around the world being interconnected. (Network Layer) Top |
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IPsec (Internet Protocol Security) |
| A framework of protocols designed to secure IP traffic between two endpoints. IPsec creates virtual private networks (VPNs) by comprising protocols that can exchange security keys privately as part of the confidential negotiation of a security association between endpoints joined by an insecure network such as the internet. (Network Layer) Top |
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IPv4 |
| The primary Layer-3 protocol in use on the internet and private intranets. Internet Protocol version 4 (IPv4), like many Layer-3 protocols, provides end-to-end logical identifiers—32-bit IPv4 addresses, represented as four, eight-bit decimal numbers separated by periods (dotted decimal notation), such as 192.168.10.1. IPv4 addresses have a hierarchical address structure that lends itself to routing. (Network Layer) Top |
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IPv6 |
| The Layer-3 protocol designed to replace IPv4. Internet Protocol version 6 (IPv6) features 128-bit addresses that provide 296 times the number of addresses possible with IPv4. Unlike the decimal-based notation used to represent IPv4 addresses, eight fields of four hexadecimal (hex, for short) digits—a total of 32— are used to represent IPv6 addresses. An example IPv6 address is 2001:0db8:1234:5678:02ab:cdff:feef:1234. (Network Layer) Top |
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P
Packet switched network |
| A network characterized by constantly variable pathways, created on demand or permanently established, through a group of switches. Unlike with circuit-switched networks, packet-switched networks require each frame of information sent have its own independent addressing information that can be used by the switching devices to forward the frame over an arbitrarily chosen pathway. Because the pathway can change from frame to frame, packet-switched networks require that the more expensive circuit emulation be used or that the user subscribes to a circuit-switched network instead. (Network Layer) Top |
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Packet |
| The data structure often associated with Layer-3 protocols. It is common to refer to an IP datagram as an IP packet. Packets are often only a portion of an entire application message that has been broken into smaller pieces to fit within the smaller limits imposed by lower-layer data structures, such as frames. (Network Layer) Top |
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Ping |
| The act of, or the utility used in, testing the availability of a remote IP host. The Internet Control Message Protocol (ICMP) is used by the ping utility to send an echo request to the remote host in question. The expectation is that an echo reply will be returned by the remote host, indicating that it is powered on and operational. If no reply is received, more troubleshooting must be performed because only a successful ping provides definitive information. (Network Layer) Top |
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R
Router |
| A Layer-3 device used in forwarding traffic from one logical segment to another to send the traffic toward the intended recipient. In TCP/IP internetworks, routers are used to forward IP traffic based on reachability information stored in the router’s routing table. (Network Layer) Top |
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Routing protocol |
| A protocol that helps to build a routing table. In addition to dynamic routing protocols, such as OSPF, EIGRP, RIP, IS-IS, and BGP, you can consider the configuration of static routes and configuring IP addresses on a device’s networking interfaces to be routing protocols in that the syntax involved in these configurations is an agreed-upon set of rules, as are all protocols. (Network Layer) Top |
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Routing table |
| A database of known network and host destinations from the perspective of the device that uses it. Each entry in a routing table contains, at a minimum, the destination to be reached, a subnet mask to allow comparison of the destination address in an IP header to the relevant portion of the destination in the table’s entry, an interface to exit through to get to the destination or to the next router in the path, the IP address of the next device to pass the packet to, and a metric to act as a final tie-breaker should there be two entries that match the intended destination. Should there be multiple matches with no way to decide which is best, the default behavior of most routers is to use up to the maximum number of paths allowed simultaneously, increasing overall available bandwidth. (Network Layer) Top |
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S
Subnetting |
| The act of splitting a larger IP address space into smaller broadcast domains known as subnetworks or subnets (not to be confused with subnet masks, or masks for short). Subnetting is especially necessary with IPv4 to save precious address blocks by splitting them into more appropriately sized segments based on the expected number of hosts present on a given subnet and on any potential future growth of that subnet. (Network Layer) Top |
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