CCNA Certification – Core Vocabulary

Key CCNA terms with concise definitions to aid exam preparation.

Router

Network device that forwards data packets between computer networks based on routing tables.

Switch

Layer-2 device that filters and forwards frames between LAN segments using MAC addresses.

Network Controller

Centralised, programmable platform used to manage, monitor and troubleshoot virtual or physical network infrastructure.

Endpoint

Host device (e.g., laptop, phone) that acts as the source or destination of network communication and often requires security controls.

Firewall

Hardware- or software-based security device that permits, denies, or drops traffic according to predefined rules.

Intrusion Prevention System (IPS)

Security application that detects, reports, and actively blocks malicious network or system activity.

Access Point (AP)

Device that connects wireless clients to a wired network, forming a WLAN.

Server

Computer dedicated to providing specific services or resources to other hosts; designed for long-term, reliable operation.

LAN (Local Area Network)

Network covering a small geographical area such as a building or campus.

MAN (Metropolitan Area Network)

Network that interconnects multiple LANs across a city-sized area.

WAN (Wide Area Network)

Network that spans large geographic distances by interconnecting multiple LANs or MANs.

SOHO Network

Small Office/Home Office network designed for entrepreneurs or small businesses operating from limited space.

Cloud Storage

Service that stores data on Internet-accessible servers, allowing access from multiple devices anywhere online.

Single-Mode Fiber (SMF)

Fiber-optic cable that carries one light mode over long distances with minimal attenuation.

Multimode Fiber (MMF)

Fiber-optic cable with a larger core that carries multiple light modes, suited for shorter distances.

Copper Cable

Data-transmission medium using electrical signals; includes coaxial, UTP, and STP types.

Ethernet

IEEE 802.3 LAN technology providing flexible, inexpensive, and widely adopted networking.

Power over Ethernet (PoE)

Technique that delivers electrical power to devices over Ethernet data cables.

Class A IP Address

Addresses whose first octet ranges 1-126 (0 and 127 reserved); binary prefix 0xxxx.

Class B IP Address

Addresses whose first octet ranges 128-191; binary prefix 10xxx.

Class C IP Address

Addresses whose first octet ranges 192-223; binary prefix 110xx.

Class D IP Address

Multicast addresses 224-239; binary prefix 1110x.

Class E IP Address

Experimental addresses 240-254; binary prefix 1111x.

Loopback Address

127.0.0.1; used by a host to send traffic to itself for testing.

Broadcast Address

All host bits set to 1 (e.g., 192.168.1.255) to reach every host on a subnet.

ARP Table

Cache holding MAC-to-IP mappings; viewed with arp -a or show ip arp.

Ping

ICMP echo utility that tests reachability of a host.

Traceroute

Tool that reveals each hop on the path to a destination.

Port Security

Switch feature limiting learned MAC addresses per port and providing violation actions (protect, restrict, shutdown).

VLAN (Virtual LAN)

Logical segmentation of Layer-2 networks into separate broadcast domains on the same switch.

Trunk Port

Switch port that carries multiple VLANs using tagging protocols such as IEEE 802.1Q.

Native VLAN

Untagged VLAN on an 802.1Q trunk; frames for this VLAN are sent without tags.

DTP (Dynamic Trunking Protocol)

Cisco protocol that negotiates trunk formation between switches.

VTP (VLAN Trunking Protocol)

Cisco protocol that distributes VLAN information between switches (server, client, transparent modes).

STP (Spanning Tree Protocol)

Layer-2 protocol preventing loops by placing switch ports into forwarding or blocking states.

BPDU Guard

STP feature that disables a port when unexpected BPDUs are received, protecting PortFast ports.

EtherChannel

Technology that aggregates up to eight physical links into one logical link for higher bandwidth and redundancy.

Access Control List (ACL)

Ordered set of permit/deny rules that filter traffic based on criteria such as source, destination, and protocol.

Inside Local Address

Private IP assigned to an internal host before NAT translation.

Inside Global Address

Public (routable) IP representing an internal host after NAT translation.

SNAT (Source NAT)

Translation that changes the source IP of outbound traffic, typically private-to-public.

DNAT (Destination NAT)

Translation that changes the destination IP of inbound traffic, commonly for port forwarding.

PAT (Port Address Translation)

Many-to-one NAT that differentiates sessions by unique TCP/UDP port numbers (NAT overload).

DHCP

Protocol that dynamically assigns IP configuration to hosts; uses UDP 67/68.

HSRP (Hot Standby Router Protocol)

Cisco redundancy protocol that presents a virtual default gateway; routers assume active/standby roles.

IP SLA

Cisco feature that generates traffic to measure network performance (e.g., ICMP-echo tests).

Telnet

Unencrypted TCP-based virtual terminal protocol used for remote CLI access (port 23).

SSH (Secure Shell)

Encrypted remote-access protocol that replaces Telnet; uses TCP 22.

TACACS+

AAA protocol providing centralised authentication, authorisation, and accounting for network devices.

SNMP

Application-layer protocol (UDP 161/162) for monitoring and managing network devices.

CDP (Cisco Discovery Protocol)

Cisco proprietary Layer-2 protocol that advertises device information to directly connected Cisco equipment.

LLDP

Open standard (IEEE 802.1AB) Layer-2 discovery protocol similar to CDP.

PPP (Point-to-Point Protocol)

Layer-2 protocol suite for point-to-point links supporting authentication (PAP/CHAP) and multilink.

PAP (Password Authentication Protocol)

Simple two-way handshake authentication method used by PPP; credentials sent in clear text.

CHAP (Challenge Handshake Authentication Protocol)

PPP authentication that uses a three-way challenge-response to avoid sending passwords in clear text.

RIP (Routing Information Protocol)

Distance-vector routing protocol using hop count; AD 120; UDP 520.

EIGRP

Cisco proprietary hybrid routing protocol (protocol 88) that calculates metrics using bandwidth and delay.

OSPF

Link-state routing protocol that uses SPF algorithm; supports areas and has AD 110.

Area Border Router (ABR)

OSPF router with interfaces in backbone area 0 and at least one non-backbone area.

Autonomous System Boundary Router (ASBR)

OSPF router that redistributes external routes into the OSPF domain.

Backbone Router

OSPF router with at least one interface in area 0.

Internal Router (OSPF)

Router with all OSPF interfaces within the same area.