CNPA key terms

A seven-layer conceptual framework describing how data moves from an application on one host to an application on another, separating physical transmission, addressing, routing, and application concerns.

A four-layer architectural model (link, internet, transport, application) that describes the protocol suite actually used on modern networks and underpins how hosts and routers are configured.

The process of wrapping data with protocol headers as it moves down the stack, so each layer adds its own control information and the receiver can strip it back off in reverse order.

The named chunk of data at a given layer, such as a frame at the data link layer, a packet at the network layer, or a segment at the transport layer.

A 48-bit hardware identifier burned into a network interface, written as six hex octets, used for delivery on a single local network segment rather than across routers.

The data link layer container that carries a source and destination MAC address, a type field, the payload, and a frame check sequence used to detect transmission errors.

A device that learns which MAC addresses live on which ports and forwards frames only out the port leading to the destination, dividing a network into separate collision domains.

A logical grouping of switch ports that behaves like a separate broadcast domain, letting one physical switch carry traffic for multiple isolated networks.

A switch link that carries frames for several VLANs at once, tagging each frame so the receiving device knows which logical network it belongs to.

The standard that inserts a four-byte tag into an Ethernet frame to identify its VLAN, including priority bits and the VLAN identifier used on trunk links.

A layer 2 protocol that blocks redundant switch links to prevent frame loops, electing a root bridge and choosing a loop-free path through the topology.

The set of devices that receive a single broadcast frame, normally bounded by routers and by VLAN boundaries on switches.

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

A shorthand that writes an IP network as an address followed by a slash and the number of leading network bits, such as 192.168.10.0/24.

A contiguous block of IP addresses carved out of a larger network by borrowing host bits, creating a smaller broadcast domain with its own network and broadcast addresses.

The highest address in an IPv4 subnet, reserved to reach every host on that subnet and therefore unusable as an address for a single interface.

An address from the ranges 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16 that is not routed on the public internet and requires translation to reach outside networks.

The address 127.0.0.1 (or any address in 127.0.0.0/8) that refers to the local host itself, used to test whether the IP stack is working.

A 128-bit address written as eight groups of hexadecimal digits, with shortened zero notation and built-in support for autoconfiguration and vastly larger address space.

An address valid only on a single local segment, such as IPv4 169.254.0.0/16 or IPv6 fe80::/10, used when no DHCP server is reachable or for local-only communication.

A device that forwards packets between different IP networks by consulting a routing table and rewriting the layer 2 headers for each hop.

The IP address of the router a host sends traffic to when the destination is not on its own subnet, making it the exit point from the local network.

A list of destination networks, next hops, and metrics that a router uses to choose the best path for each packet it forwards.

A forwarding entry an administrator configures by hand for a destination network, which does not adapt automatically to topology changes unless it is removed or replaced.

A method where routers exchange reachability information using a protocol such as OSPF or RIP, automatically recalculating paths when links fail or change.

A trust ranking a router assigns to the source of a route, so that when two protocols offer the same destination the lower value is installed in the table.

A protocol that automatically leases IP addresses, subnet masks, default gateways, and DNS servers to clients, using a four-message exchange of discover, offer, request, and acknowledge.

A hierarchical naming system that resolves human-readable hostnames to IP addresses, using recursive resolvers and cached records with time-to-live values.

A protocol that maps a known IPv4 address to the corresponding MAC address on the local segment by broadcasting a request and caching the reply.

The IPv6 protocol suite that replaces ARP for address resolution, discovers routers, and performs stateless address autoconfiguration using ICMPv6 messages.

A technique that rewrites IP addresses and ports as packets cross a router, letting many private hosts share one public address and hiding internal addressing from outside networks.

The name that identifies a wireless network, broadcast in beacon frames so clients can discover and associate with the correct access point.

A device that bridges wireless clients onto a wired network, managing association, authentication, and radio channel usage for the stations in its coverage area.

A Wi-Fi security standard using AES-based encryption with either a pre-shared key or an enterprise authentication server, replacing the weaker WEP and original WPA.

A centralized authentication, authorization, and accounting server protocol commonly used with enterprise Wi-Fi so users authenticate with individual credentials rather than a shared key.

The process of a wireless client moving its association from one access point to another while keeping its session, which depends on overlapping coverage and consistent security settings.

A device or software filter that permits or denies traffic based on rules about addresses, ports, and protocols, often tracking connection state to allow return traffic.

An ordered list of permit and deny statements applied to an interface or resource, evaluated top to bottom until the first match determines the action.

A screened network segment that hosts services reachable from the internet while keeping them separated from the internal trusted network.

A utility that sends ICMP echo requests to test whether a host is reachable and to measure round-trip time, revealing basic connectivity and latency problems.

A diagnostic tool that reveals each router along a path by sending packets with increasing time-to-live values and recording where they expire.

The largest payload a link can carry in one frame, which constrains packet size and causes fragmentation or dropped traffic when exceeded without proper handling.

A flood of broadcast or multicast frames that circulates through a looped layer 2 topology, consuming bandwidth until the loop is broken.