LCPE key terms

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

A four-layer architectural model (application, transport, internet, network access) that describes the protocols actually used on modern networks, including IP, TCP, UDP, and Ethernet.

The process of wrapping data with protocol-specific headers (and trailers) as it moves down the stack, so each layer adds the information its peer layer needs to deliver the payload.

The named chunk of data at a given layer: frame at the data link layer, packet at the network layer, and segment (TCP) or datagram (UDP) at the transport layer.

A 48-bit hardware identifier burned into a network interface, written as six hexadecimal octets, used by Ethernet to deliver frames to a specific NIC on the local segment.

Address Resolution Protocol; a host broadcasts a request asking which MAC address owns a given IPv4 address, and the owner replies so frames can be built for local delivery.

A logical Layer 2 segmentation of a switch into separate broadcast domains, configured per port or by tagging, letting one physical switch carry isolated groups of devices.

A link that carries multiple VLANs by inserting a 4-byte tag into each Ethernet frame, with the VLAN ID identifying which logical network the frame belongs to.

The VLAN whose frames travel untagged on an 802.1Q trunk. Both ends must agree on it, otherwise traffic leaks between VLANs or is dropped.

The set of devices that receive a single broadcast frame. Routers and VLAN boundaries stop broadcasts, while switches and hubs forward them to every port in the domain.

Spanning Tree Protocol; switches elect a root bridge and block redundant links so that Layer 2 topologies stay loop-free while still providing backup paths.

The switch elected as the reference point of a spanning tree, chosen by lowest bridge ID (priority plus MAC address); all path costs are measured from it.

Bundling several physical switch links into one logical link to increase bandwidth and provide redundancy, with LACP or PAgP negotiating the bundle.

Link Aggregation Control Protocol, an IEEE standard (802.3ad) that negotiates which physical links join an EtherChannel bundle and monitors their health.

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 identify the host.

Writing an IPv4 prefix length after a slash, such as /24, to state how many leading bits are the network portion, replacing dotted-decimal subnet masks.

The router address a host sends traffic to when the destination is not on its own subnet; without a correct gateway, off-subnet communication fails.

The list of known destinations, next hops, outgoing interfaces, and metrics a router or host consults to decide where to forward each packet.

A trust ranking (0-255) used by a router to choose between routes to the same prefix learned from different sources; lower values win, and 255 is never installed.

The forwarding rule that, among all routes matching a destination address, the router uses the one with the most specific (longest) prefix length.

Open Shortest Path First; a link-state interior gateway protocol that floods link information within an area and runs Dijkstra's algorithm to compute lowest-cost paths.

Advertising one aggregate prefix that covers many more-specific networks, shrinking routing tables and limiting the scope of topology changes.

Dynamic Host Configuration Protocol; a server leases IPv4 addresses, masks, gateways, and DNS servers to clients, using the DORA exchange of discover, offer, request, and acknowledge.

Domain Name System; a hierarchical, distributed database that resolves human-readable names into IP addresses, using record types such as A, AAAA, CNAME, and MX.

Network Address Translation; a router rewrites source or destination IP addresses (and often ports) as packets cross between networks, commonly letting many private hosts share one public address.

Port Address Translation, also called NAT overload; many internal hosts share one public IP address, distinguished by unique source port numbers in the translation table.

Network Time Protocol; synchronizes device clocks to a reference time source over UDP port 123, which keeps log timestamps, certificates, and authentication consistent.

A standard for sending event messages from network devices to a central collector, with severity levels from 0 (emergency) to 7 (debugging) and UDP port 514 by default.

Simple Network Management Protocol; managers poll or receive traps from agents about device health, reading and writing variables organized in a management information base.

Access Control List; an ordered set of permit and deny rules applied to an interface or line that filters traffic by addresses, protocols, and ports, stopping at the first match.

Authentication, Authorization, and Accounting; the framework that verifies who a user is, what they may do, and records what they did, often via a RADIUS or TACACS+ server.

A UDP-based protocol that centralizes authentication and authorization for network access, commonly used for VPN, wireless, and device login, and it encrypts only the password.

A switch feature that limits which and how many MAC addresses may appear on an access port, and can shut down, restrict, or protect the port on violation.

A switch safeguard that marks ports as trusted or untrusted and drops DHCP server messages arriving on untrusted ports, preventing rogue servers from handing out addresses.

A suite of protocols that encrypts and authenticates IP traffic, using IKE to negotiate security associations, AH for integrity, and ESP for confidentiality and integrity.

An encrypted logical path between two endpoints across an untrusted network, encapsulating original packets so they appear as ordinary payload to intermediate devices.

An interface style where clients use HTTP methods such as GET, POST, PUT, and DELETE on resource URLs, typically exchanging JSON, to read or change device configuration.

JavaScript Object Notation; a text format of key-value pairs, objects, and arrays that is widely used for configuration data and API request and response bodies.

A data modeling language that defines the structure and constraints of configuration and state data, used by NETCONF and RESTCONF to describe device models.

An architecture where a central controller computes and pushes policy and forwarding intent to many devices, giving a network-wide view instead of per-device configuration.

Managing networks and servers through version-controlled, machine-readable definition files that tools apply automatically, making deployments repeatable and auditable.

An agentless automation tool that connects over SSH or API calls and runs playbooks written in YAML to configure devices in a defined order.