Use this alongside the lessons. The short definition introduces the idea; the lesson supplies its limits and examples.
- ACL
- Access control list: ordered rules that match traffic and decide an action.
- API
- A defined interface that lets one program ask another program for data or an action.
- ARP
- IPv4 local-link address resolution: finding the link-layer address of a next hop.
- Accounting
- Recording activity for later review.
- Address
- A value used to identify a destination or interface in a particular addressing system.
- Administrative distance
- A local preference used when selecting between route sources offering the same prefix.
- Authentication
- Checking an identity.
- Authorisation
- Deciding which actions an identity may perform.
- Bandwidth
- The data-carrying capacity of a link; it differs from actual application throughput.
- Broadcast
- A message intended for all recipients in the relevant broadcast domain; IPv6 uses other mechanisms instead.
- CIDR prefix
- The slash-number notation indicating how many leading address bits identify a network.
- Cloud
- Provider-operated computing services accessed through networks, with provider-specific resource and billing rules.
- Container
- An isolated application process environment, commonly sharing the host environment’s kernel.
- Control plane
- The logic that decides how forwarding should work.
- DHCP
- A service/protocol that can lease addresses and supply other host network settings.
- DNS
- A distributed naming system that answers questions about records, including address records.
- Data plane
- The part of the system that forwards packets.
- Default gateway
- The next-hop router a host uses for destinations without a more specific route.
- Encapsulation
- Wrapping information in another protocol’s headers so it can be carried.
- EtherChannel
- Compatible physical links combined into a logical port-channel.
- Firewall
- A system enforcing traffic policy; its exact inspection and state behaviour depend on the product and configuration.
- Frame
- A link-layer unit of data, such as an Ethernet frame.
- Hypervisor
- Software that creates and manages virtual machines.
- ICMP
- An IP-related control and diagnostic protocol family; ping uses echo messages.
- IP address
- A network-layer address assigned to an interface or used to identify an IP destination.
- Idempotence
- A property where repeating an operation does not keep changing the intended end state.
- Interface
- A physical or logical connection point on a device.
- JSON
- A text data format using objects, arrays and defined value types.
- LACP
- A protocol that negotiates supported link aggregation.
- LLDP
- An industry-standard protocol for advertising information to directly connected neighbours.
- Latency
- Time taken for delivery or response; specify whether a measurement is one-way or round-trip.
- Lease
- A time-bounded allocation, such as an address assigned by DHCP.
- MAC address
- A link-layer address used in local delivery. It is not a reliable human identity.
- MTU
- Maximum transmission unit: the largest packet size a link/interface carries without the relevant fragmentation or size-handling mechanism.
- Metric
- A routing protocol’s measure for comparing paths according to that protocol.
- NAT
- Network address translation: changing addressing according to a mapping rule, not encrypting traffic.
- NDP
- IPv6 Neighbor Discovery, using ICMPv6 messages for local-link functions including address resolution and router discovery.
- OSPF
- A link-state routing protocol that exchanges network information and calculates paths using cost.
- PAT
- Port address translation, often called NAT overload, allowing conversations to share translated addressing.
- Packet
- A network-layer unit of information, such as an IP packet.
- PoE
- Power over Ethernet on supported equipment and cable connections.
- Port
- A physical connection on a device, or a transport-layer number identifying a service/conversation; the context matters.
- QoS
- Quality of service: mechanisms for classifying and handling traffic, especially under contention.
- Route
- An instruction describing how to reach a destination prefix.
- Router
- A device/function that forwards IP packets between networks.
- SLAAC
- IPv6 stateless address autoconfiguration using information from router advertisements.
- SSH
- An encrypted protocol commonly used for remote command access.
- SSID
- The name identifying a wireless LAN.
- STP
- Spanning Tree Protocol: mechanisms that prevent Layer 2 forwarding loops while permitting redundant paths.
- Subnet
- An address range defined by a prefix within a network design.
- Switch
- A device/function forwarding local link-layer frames; multilayer switches can also route.
- TCP
- A transport protocol providing an ordered byte stream with reliability mechanisms.
- Trunk
- A link configured to carry multiple VLANs in this switching context.
- UDP
- A datagram transport without TCP’s built-in ordering and retransmission mechanisms.
- VLAN
- A virtual LAN: a separate Layer 2 broadcast domain.
- VM
- Virtual machine: a guest operating system running on virtualised hardware.
- VPN
- A virtual private network; the security properties depend on the protocol and configuration.
- VRF
- A separate routing context, not encryption by itself.
- WLC
- Wireless LAN controller: a system managing supported access points and wireless policies.
Sources & content checks
Technical references checked on 25 October 2026. These are original teaching explanations, not official Cisco course material. See how content and lab validation are described.