Networking Glossary
A comprehensive reference of networking terms and definitions to help you understand CCNA concepts and terminology.
A
Access Control List (ACL)
A set of rules that control network traffic and may permit or deny packets at router interfaces based on specified criteria.
Access Layer
The layer in the hierarchical network design model that provides connectivity to end devices and users.
Address Resolution Protocol (ARP)
A protocol used to map an IP address to a MAC address on a local network.
Administrative Distance (AD)
A value assigned to routing protocols to determine preference when multiple routes to the same destination exist.
Autonomous System (AS)
A collection of networks under a common administrative domain.
Authentication
The process of verifying the identity of a user, device, or system.
B
Bandwidth
The maximum data transfer rate of a network or internet connection.
Border Gateway Protocol (BGP)
An exterior gateway protocol designed to exchange routing information between autonomous systems.
Broadcast Domain
A logical division of a computer network where all nodes can reach each other by broadcast at the data link layer.
Broadcast Address
A network address used to transmit to all devices on a multiple-access network.
C
CIDR (Classless Inter-Domain Routing)
A method for allocating IP addresses and routing IP packets that replaced the previous classful network addressing architecture.
Cisco Discovery Protocol (CDP)
A proprietary protocol that allows Cisco devices to share information about other directly connected Cisco equipment.
Collision Domain
A network segment where data packets can collide with one another when sent simultaneously.
Core Layer
The backbone of the network in the hierarchical network design model, responsible for fast and reliable data transport.
D
Default Gateway
A node (usually a router) that serves as an access point to other networks.
DHCP (Dynamic Host Configuration Protocol)
A network protocol that automatically assigns IP addresses and other network configuration parameters to devices.
Distance Vector Routing Protocol
A class of routing protocols that use the Bellman-Ford algorithm to calculate paths, such as RIP.
DNS (Domain Name System)
A hierarchical and decentralized naming system for computers, services, or other resources connected to the Internet or a private network.
Duplex
A communication mode where data can be transmitted in both directions on a signal carrier.
E
EGP (Exterior Gateway Protocol)
A routing protocol used to exchange routing information between different autonomous systems.
Encapsulation
The process of adding headers and trailers to data as it moves down the OSI model layers.
Ethernet
A family of computer networking technologies commonly used in LANs, MANs, and WANs.
EtherChannel
A port link aggregation technology that groups multiple physical Ethernet links into one logical link for increased bandwidth and redundancy.
F
Firewall
A network security device that monitors and filters incoming and outgoing network traffic based on predetermined security rules.
Frame
A data packet at the Data Link Layer (Layer 2) of the OSI model.
Frame Relay
A standardized wide area network technology that specifies the physical and logical link layers of digital telecommunications channels.
FTP (File Transfer Protocol)
A standard network protocol used for transferring files between a client and server on a computer network.
G
Gateway
A networking device that connects networks with different protocols or architectures.
GRE (Generic Routing Encapsulation)
A tunneling protocol developed by Cisco that can encapsulate a wide variety of network layer protocols inside virtual point-to-point links.
H
HSRP (Hot Standby Router Protocol)
A Cisco proprietary redundancy protocol that allows multiple routers to present a single virtual router to the hosts on a LAN.
HTTP (Hypertext Transfer Protocol)
An application protocol for distributed, collaborative, hypermedia information systems.
Hub
A basic networking device that connects multiple Ethernet devices together, making them act as a single network segment.
I
ICMP (Internet Control Message Protocol)
A network layer protocol used by network devices to diagnose network communication issues.
IGP (Interior Gateway Protocol)
A routing protocol used within an autonomous system.
IP Address
A numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
IPv4
The fourth version of the Internet Protocol, using 32-bit addresses.
IPv6
The most recent version of the Internet Protocol, using 128-bit addresses.
ISAKMP (Internet Security Association and Key Management Protocol)
A protocol for establishing security associations and cryptographic keys in an Internet environment.
J
Jitter
The variation in the delay of received packets in a network.
L
LAN (Local Area Network)
A computer network that interconnects computers within a limited area such as a residence, school, or office building.
LACP (Link Aggregation Control Protocol)
A protocol for the collective handling of multiple physical ports that can be seen as a single channel.
Link-State Routing Protocol
A routing protocol that uses Dijkstra's algorithm to determine the shortest path, such as OSPF.
M
MAC Address
A unique identifier assigned to a network interface controller for use as a network address in communications within a network segment.
MAN (Metropolitan Area Network)
A computer network that interconnects users with computer resources in a geographic area larger than a LAN but smaller than a WAN.
MTU (Maximum Transmission Unit)
The size of the largest protocol data unit that can be communicated in a single network layer transaction.
Multicast
A group communication where data transmission is addressed to a group of destination computers simultaneously.
N
NAT (Network Address Translation)
A method of remapping one IP address space into another by modifying network address information.
NETCONF (Network Configuration Protocol)
A network management protocol developed and standardized by the IETF to install, manipulate, and delete the configuration of network devices.
NTP (Network Time Protocol)
A networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks.
O
OSPF (Open Shortest Path First)
A routing protocol for IP networks that uses a link-state routing algorithm and falls into the group of interior gateway protocols.
OSI Model
A conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology.
P
PAT (Port Address Translation)
A type of NAT that maps multiple private IP addresses to a single public IP address using different ports.
Ping
A computer network administration software utility used to test the reachability of a host on an Internet Protocol network.
PoE (Power over Ethernet)
A technology that allows electrical power to pass along with data on Ethernet cabling.
PPP (Point-to-Point Protocol)
A data link protocol used to establish a direct connection between two nodes.
Q
QoS (Quality of Service)
The description or measurement of the overall performance of a service, particularly the performance seen by the users of the network.
R
RADIUS (Remote Authentication Dial-In User Service)
A networking protocol that provides centralized Authentication, Authorization, and Accounting management for users who connect and use a network service.
RIP (Routing Information Protocol)
One of the oldest distance-vector routing protocols which uses hop count as a routing metric.
Router
A networking device that forwards data packets between computer networks.
Routing Table
A data table stored in a router or a network host that lists the routes to particular network destinations.
S
STP (Spanning Tree Protocol)
A network protocol that builds a loop-free logical topology for Ethernet networks.
Subnet
A logical subdivision of an IP network.
Subnet Mask
A 32-bit number that masks an IP address and divides the IP address into network address and host address.
Switch
A networking device that connects devices on a computer network by using packet switching to receive and forward data to the destination device.
T
TCP (Transmission Control Protocol)
A connection-oriented protocol that provides reliable, ordered, and error-checked delivery of a stream of bytes between applications.
Telnet
A protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communication facility.
TFTP (Trivial File Transfer Protocol)
A simple, lockstep, file transfer protocol which allows a client to get a file from or put a file onto a remote host.
Traceroute
A computer network diagnostic tool for displaying the route and measuring transit delays of packets across an IP network.
U
UDP (User Datagram Protocol)
A connectionless protocol that provides a simple but unreliable message service.
Unicast
A one-to-one transmission from one point in the network to another point.
V
VLAN (Virtual Local Area Network)
A logical subnetwork that groups a collection of devices from different physical LANs.
VPN (Virtual Private Network)
A technology that creates a safe and encrypted connection over a less secure network, such as the internet.
VRF (Virtual Routing and Forwarding)
A technology that allows multiple instances of a routing table to co-exist within the same router at the same time.
VTP (VLAN Trunking Protocol)
A Cisco proprietary protocol that propagates the definition of VLANs on the whole local area network.
W
WAN (Wide Area Network)
A telecommunications network that extends over a large geographical area for the primary purpose of computer networking.
Wildcard Mask
A mask used in Cisco IOS to specify which IP addresses should be matched in access control lists and routing protocols.
Wireless LAN
A wireless computer network that links two or more devices using wireless communication to form a local area network within a limited area.