CCNA key terms

A seven-layer reference framework that describes how data moves from an application on one host to an application on another, separating functions such as addressing, routing, and reliable delivery into named layers.

A connection-oriented transport protocol that uses a three-way handshake, sequence numbers, and acknowledgments to deliver a reliable, ordered byte stream between applications.

A connectionless transport protocol that sends datagrams without handshakes, acknowledgments, or retransmission, making it fast and low-overhead but unreliable.

A 32-bit value of contiguous ones followed by zeros that tells a device which bits of an IPv4 address identify the network and which bits identify the host.

A shorthand way to write an IPv4 or IPv6 prefix, where the address is followed by a slash and a number showing how many leading bits are the network portion.

A 48-bit hardware address assigned to a network interface, written as six hexadecimal bytes, used by Ethernet to deliver frames to a device on the local segment.

A logically separate Layer 2 broadcast domain created on switches, letting devices on different ports behave as if they were on separate physical networks.

A switch port configured for a single VLAN that connects to an end device and sends and receives untagged Ethernet frames.

A switch port that carries traffic for multiple VLANs between switches or to a router, tagging frames with 802.1Q headers so VLAN membership is preserved.

A Layer 2 protocol that builds a loop-free topology by electing a root bridge, choosing root and designated ports, and blocking redundant links.

A configuration that bundles several physical switch links into one logical link, increasing bandwidth and providing redundancy while spanning tree sees a single port.

The name that identifies a wireless network, carried in beacon frames so that client devices can discover and associate with the correct WLAN.

A device or software that centrally manages many access points, handling configuration, roaming, and wireless security policy in one place instead of per access point.

The IP address of a router interface on the local subnet that hosts send packets to when the destination lies outside their own network.

A list kept by a router showing known destination networks, the next hop or exit interface for each, and the metric or source of the route.

A number from 0 to 255 that rates how trustworthy a route source is; lower values win when different protocols offer a route to the same network.

A route manually entered by an administrator that tells the router where to send traffic for a specific destination, and that does not adapt automatically to topology changes.

An open-standard link-state interior routing protocol that floods link information, builds a common topology database, and runs the shortest-path-first algorithm to select routes.

A protocol that resolves a known IPv4 address to an unknown MAC address on the local link by broadcasting a request and caching the unicast reply.

A protocol that automatically supplies hosts with an IP address, subnet mask, default gateway, and DNS servers through a discover, offer, request, and acknowledge exchange.

A hierarchical naming system that translates human-readable domain names into IP addresses so applications can reach servers without hard-coded addresses.

A technique that rewrites IP addresses in packet headers as traffic crosses a router, commonly letting many private hosts share a few public addresses.

A protocol that synchronizes clocks across devices to a common time source, keeping log timestamps consistent and supporting certificate and authentication validity checks.

A management protocol in which an agent on a device reports status and sends traps to a central manager, using a tree of object identifiers.

A standard for sending event messages from network devices to a logging server, with each message carrying a facility and a severity level.

A simple, connectionless file transfer protocol over UDP that network devices use to save and load configurations and operating system images.

An encrypted protocol for remote command-line access to network devices, replacing insecure Telnet by protecting credentials and session data in transit.

An ordered list of permit and deny statements applied to an interface or line that matches traffic by addresses, ports, or protocol to filter packets.

A framework that separates authentication of users, authorization of what they may do, and accounting of what they did, often using a central server such as RADIUS or TACACS+.

A switch feature that limits which and how many MAC addresses may use a port, and can shut down or restrict the port when a violation occurs.

A switch feature that marks ports as trusted or untrusted and drops DHCP server messages arriving on untrusted ports, preventing rogue servers and address spoofing.

A wireless security standard using AES-CCMP encryption with either a pre-shared key or 802.1X authentication to protect traffic sent over the air.

An interface style where clients use HTTP methods such as GET, POST, PUT, and DELETE on resource URLs, usually exchanging data in JSON or XML.

A lightweight text format for structured data using objects, arrays, strings, numbers, booleans, and null, widely used by APIs and automation tools.

An agentless automation tool that pushes configuration to network devices over SSH using plain-text playbooks written in YAML.

An architecture that separates the control plane, which decides where traffic goes, from the data plane, which forwards it, letting a central controller program devices.