CompTIA Network+ key terms

A seven-layer reference model describing how data travels from an application on one device to an application on another, with each layer handling a distinct job such as framing, addressing, routing, or delivery.

The process of wrapping data with protocol headers as it moves down a network stack, so each layer receives the information it needs to deliver and decode the payload correctly.

A 32-bit value that tells a host which portion of an IPv4 address identifies the network and which portion identifies the host, letting devices decide whether traffic is local or must be routed.

A shorthand for writing an IP network using a slash and a prefix length, such as /24, where the number states how many leading bits belong to the network portion of the address.

A logical grouping of switch ports or devices that behaves like its own separate network, keeping broadcast traffic contained without requiring dedicated physical hardware for each group.

The router address a host sends traffic to when the destination is not on the local subnet; without a correct gateway, a device reaches local peers but nothing beyond them.

A technique that rewrites IP addresses in packet headers as traffic crosses a router, letting many private hosts share one public address and hiding internal addressing from outside networks.

A hierarchical, distributed naming system that translates human-readable host names into IP addresses so clients can locate servers without knowing their numeric addresses in advance.

A protocol that automatically supplies clients with an IP address, subnet mask, default gateway, and DNS servers from a pool, removing the need to configure each device by hand.

A protocol used on IPv4 local networks to map a known IP address to the hardware MAC address of the device that owns it, so frames can be delivered on the segment.

Every device that receives a frame sent to the broadcast address of a network segment; routers and VLANs create boundaries that stop broadcasts from spreading further.

A network switch that administrators can configure and monitor, offering features such as VLANs, port mirroring, link aggregation, and spanning tree control that unmanaged switches lack.

A Layer 2 protocol that prevents switching loops by electing a root bridge and blocking redundant paths, keeping a loop-free topology that can still fail over when a link drops.

An IEEE standard that lets two devices negotiate bundling several physical links into one logical link, adding bandwidth and redundancy while avoiding the forwarding problems of accidental loops.

A feature that delivers both data and electrical power over a standard Ethernet cable, letting devices such as access points, cameras, and phones run without a separate power outlet.

A device that bridges wireless clients onto a wired network, broadcasting one or more SSIDs and managing radio channels, security settings, and client associations for its coverage area.

Optical cable with a very narrow core that carries a single light path, supporting long distances and high bandwidth; it typically uses laser optics rather than cheaper LED transmitters.

A software-defined approach to wide area networking that centrally manages traffic across multiple links such as broadband, MPLS, and cellular, steering each application over the best available path.

A protocol for polling and receiving alerts from network devices, where an agent on each device reports values from a management information base to a central monitoring station.

A standard for sending log messages from network devices to a central server, giving administrators one place to search events, retain records, and trigger alerts on patterns.

A feature that summarizes traffic flows through a router or switch, recording source, destination, ports, and byte counts so analysts can see who is talking to whom and how much.

A recorded snapshot of normal performance and configuration captured when a system is healthy, used later to judge whether current behavior is a real fault or ordinary variation.

Paired recovery targets: the recovery point objective is the maximum tolerable data loss measured in time, while the recovery time objective is the maximum acceptable time to restore service after an outage.

A formal agreement between a provider and a customer that states expected service levels, such as uptime percentages, latency limits, and the remedies owed when those targets are missed.

A controlled process for proposing, reviewing, scheduling, and documenting modifications to network systems, intended to reduce outages caused by unplanned or untested alterations.

A security device that tracks active connections and permits return traffic automatically, deciding on packets using session state, addresses, ports, and configured policy rather than judging each packet alone.

A monitoring system that inspects traffic for attack signatures or anomalies; an IDS only alerts, while an IPS sits inline and can block the traffic it flags.

A set of protocols that encrypts and authenticates traffic between sites or remote users over an untrusted network, commonly using IKE for key exchange and ESP for the protected payload.

A port-based access control standard that keeps a switch port or wireless association closed until the connecting device proves its identity to an authentication server.

A central authentication protocol that verifies user or device credentials for network access and returns authorization attributes, commonly paired with 802.1X on switches and wireless controllers.

A segmented network sitting between the internet and the internal network, hosting public-facing servers so that a compromise there does not give attackers direct access to internal systems.

A security model that grants no implicit trust based on network location; every request is authenticated, authorized, and logged, and access is limited to the minimum required.

The practice of giving each user, service, or device only the permissions it needs to do its job, limiting the damage that a stolen credential or compromised account can cause.

A utility that sends ICMP echo requests to a target and reports whether replies arrive and how long they take, giving a quick test of basic reachability and round-trip time.

A tool that reveals the routers along the path to a destination by sending packets with increasing hop limits and recording where each probe expires, helping locate where traffic is lost.

The recording of actual frames or packets on an interface for later analysis, showing protocol details, retransmissions, and errors that summary statistics alone cannot reveal.

A copper cable test that sends a pulse down the wire and measures reflections to estimate the distance to a break or short, helping technicians locate a fault rather than merely confirm one.

An instrument that injects light pulses into a fiber link and analyzes reflected and scattered light to measure loss, locate splices and breaks, and report distance along the cable.

A condition where two connected interfaces disagree about full- versus half-duplex operation, producing collisions, late collisions, and poor throughput that worsen as traffic rises.

Variation in the delay between packets arriving at a destination; small amounts are harmless to file transfers but cause choppy voice and video where timing matters.