Networking Acronyms – A–Z Reference

Every acronym you will encounter in CCNA study and real-world networking, listed alphabetically with a one-line definition and a direct link to the full explanation page. Use the jump-bar below to skip to any letter instantly.

A ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
AAA	Authentication, Authorisation, Accounting	Security framework that verifies identity, controls access rights, and logs activity	AAA Overview
ACL	Access Control List	Ordered list of permit/deny rules applied to router or switch interfaces to filter traffic	ACL Overview
AD	Administrative Distance	Trustworthiness rating (0–255) used by a router to choose between routes from different sources	Administrative Distance
AES	Advanced Encryption Standard	Symmetric block cipher used in WPA2/WPA3 and IPsec ESP; 128, 192, or 256-bit key lengths; the current gold-standard for wireless and VPN encryption	Wi-Fi Security
AP	Access Point	Wireless device that connects Wi-Fi clients to a wired LAN	Access Points & WLC
ARP	Address Resolution Protocol	Layer 2 protocol that maps a known IPv4 address to an unknown MAC address on the local segment	ARP Cache (arp -a)
AS	Autonomous System	Collection of IP prefixes under a single administrative domain that presents a unified routing policy to the Internet; identified by an ASN	BGP Overview
ASN	Autonomous System Number	Unique number identifying an autonomous system for BGP routing	BGP Overview

B ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
BDR	Backup Designated Router	OSPF backup router that takes over if the DR fails on a multi-access segment	OSPF DR/BDR
BGP	Border Gateway Protocol	Exterior path-vector routing protocol used to exchange routes between autonomous systems on the Internet	BGP Overview
BPDU	Bridge Protocol Data Unit	STP control frame exchanged between switches to elect the root bridge and determine port roles	PortFast & BPDU Guard
BUM	Broadcast, Unknown-unicast, Multicast	Three traffic types that must be flooded in overlay networks such as VXLAN	VLANs

C ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
CAM	Content Addressable Memory	Hardware table in a switch that stores MAC-address-to-port mappings for fast frame forwarding	CAM Table
CDP	Cisco Discovery Protocol	Cisco-proprietary Layer 2 protocol that advertises device identity, platform, and capability to directly connected neighbours	show cdp neighbors
CIDR	Classless Inter-Domain Routing	IP addressing scheme that replaces class-based addressing with variable-length prefix notation (e.g. /22)	Subnetting
CLI	Command Line Interface	Text-based interface used to configure and manage Cisco IOS devices	Cisco IOS Modes
CoS	Class of Service	3-bit field in the 802.1Q VLAN tag (also called PCP) used to mark frames for QoS prioritisation at Layer 2; values 0–7	QoS Marking
CRC	Cyclic Redundancy Check	Error-detection algorithm used in the Ethernet FCS field to detect frame corruption	show interfaces
CSMA/CD	Carrier Sense Multiple Access / Collision Detection	Legacy Ethernet access method where devices detect and recover from collisions on shared media	Ethernet Standards

D ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
DAI	Dynamic ARP Inspection	Switch security feature that validates ARP packets against the DHCP snooping binding table to prevent ARP spoofing	Dynamic ARP Inspection
DHCP	Dynamic Host Configuration Protocol	Application-layer protocol that automatically assigns IP addresses, subnet masks, gateways, and DNS servers to hosts	DHCP
DMZ	Demilitarised Zone	Network segment between the internet and the internal LAN that hosts publicly accessible servers	Firewall
DMVPN	Dynamic Multipoint VPN	Cisco WAN architecture that builds dynamic spoke-to-spoke tunnels on demand over a hub-and-spoke GRE/IPsec overlay	DMVPN
DNS	Domain Name System	Hierarchical distributed database that resolves human-readable hostnames (e.g. netstuts.com) to IP addresses	DNS How It Works
DR	Designated Router	OSPF router elected on a multi-access segment to reduce the number of adjacencies by acting as a hub for LSA flooding	OSPF DR/BDR
DSCP	Differentiated Services Code Point	6-bit field in the IP header used to mark packets for QoS treatment (e.g. EF for voice, AF41 for video)	QoS Marking
DTP	Dynamic Trunking Protocol	Cisco-proprietary protocol that automatically negotiates trunk links between switches	Access & Trunk Ports

E ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
EAP	Extensible Authentication Protocol	Authentication framework used in 802.1X that supports multiple credential methods (certificates, tokens, passwords)	802.1X
EIGRP	Enhanced Interior Gateway Routing Protocol	Cisco advanced distance-vector routing protocol using DUAL algorithm; supports unequal-cost load balancing	EIGRP Overview
ESP	Encapsulating Security Payload	IPsec protocol that provides confidentiality, integrity, and optional authentication by encrypting the IP packet payload; protocol number 50	IPsec Basics
EtherChannel	EtherChannel (branded term)	Logical bundling of multiple physical links into one high-bandwidth, redundant logical interface	EtherChannel Config

F ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
FCS	Frame Check Sequence	4-byte CRC trailer appended to every Ethernet frame for error detection; discarded and recalculated at each router hop	Frame Forwarding
FHRP	First Hop Redundancy Protocol	Family of protocols (HSRP, VRRP, GLBP) that provide a virtual default gateway IP shared between multiple routers	HSRP
FLSM	Fixed-Length Subnet Masking	Subnetting method where all subnets use the same prefix length, wasting addresses on small segments	Subnetting
FTP	File Transfer Protocol	Application-layer protocol for transferring files between hosts; uses TCP ports 20 (data) and 21 (control); sends credentials in plaintext	FTP

G ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
GLBP	Gateway Load Balancing Protocol	Cisco FHRP that provides both gateway redundancy and load balancing across multiple active routers	VRRP & GLBP
GRE	Generic Routing Encapsulation	Tunnelling protocol that encapsulates any Layer 3 protocol inside IP packets, commonly used with IPsec or DMVPN	GRE Tunnels

H ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
HSRP	Hot Standby Router Protocol	Cisco FHRP where one active router forwards traffic and a standby router takes over if the active router fails	HSRP
HTTP	HyperText Transfer Protocol	Application-layer protocol for web communication; operates over TCP port 80; transfers data in plaintext	HTTP & HTTPS
HTTPS	HyperText Transfer Protocol Secure	HTTP encrypted with TLS; operates over TCP port 443; standard for secure web browsing and REST APIs	HTTP & HTTPS

I ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
ICMP	Internet Control Message Protocol	Layer 3 protocol used for error reporting and diagnostics; underpins ping and traceroute	Ping
IDS	Intrusion Detection System	Passive security system that monitors traffic and alerts on suspicious activity without blocking it	Firewall
IETF	Internet Engineering Task Force	Standards organisation that publishes RFCs defining Internet protocols (IP, TCP, BGP, YANG models, etc.)	JSON, XML & YANG
IGP	Interior Gateway Protocol	Routing protocol that exchanges routes within a single autonomous system; examples include OSPF, EIGRP, and RIP	Administrative Distance
IGRP	Interior Gateway Routing Protocol	Obsolete Cisco distance-vector IGP superseded by EIGRP	EIGRP Overview
IKE	Internet Key Exchange	Protocol used in IPsec VPNs to authenticate peers and negotiate encryption keys; IKEv2 is the modern standard	IPsec Basics
IOS	Internetwork Operating System	Cisco's proprietary network operating system that runs on routers and switches	Cisco IOS Modes
IP	Internet Protocol	Layer 3 connectionless protocol responsible for logical addressing and packet routing between networks	IP Addresses
IPAM	IP Address Management	Tools and practices for planning, tracking, and managing IP address space across a network	Network Baseline
IPsec	Internet Protocol Security	Suite of protocols (AH, ESP, IKE) that provides authentication and encryption for IP packets; used in VPNs	IPsec Basics
IPFIX	IP Flow Information Export	IETF-standard flow export protocol (RFC 7011) based on NetFlow v9; vendor-neutral traffic analysis	NetFlow
IPS	Intrusion Prevention System	Inline security system that monitors traffic and actively blocks suspicious or malicious flows	Firewall
IS-IS	Intermediate System to Intermediate System	Link-state IGP used primarily in service provider networks; similar to OSPF but runs directly over Layer 2	Administrative Distance

J ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
JSON	JavaScript Object Notation	Lightweight key-value data format used in REST APIs and RESTCONF for encoding network configuration data	JSON, XML & YANG

L ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
LACP	Link Aggregation Control Protocol	IEEE 802.3ad open-standard protocol that negotiates EtherChannel formation between switches	EtherChannel PAgP & LACP
LAN	Local Area Network	Network confined to a single building or campus, typically using Ethernet and Wi-Fi	LAN
LLDP	Link Layer Discovery Protocol	IEEE 802.1AB vendor-neutral neighbour discovery protocol equivalent to CDP	show lldp neighbors
LSA	Link State Advertisement	OSPF control packet that describes a router's links and their costs; flooded to all routers to build the topology database	OSPF Areas & LSAs
LSDB	Link State Database	OSPF table containing all received LSAs; each router in an area has an identical LSDB	OSPF Areas & LSAs

M ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
MAC	Media Access Control	48-bit hardware address burned into a NIC that identifies a device at Layer 2; local-link scope only	MAC Address
MAN	Metropolitan Area Network	Network spanning a city or large campus, larger than a LAN but smaller than a WAN	MAN
MIB	Management Information Base	Hierarchical database of OIDs defining the variables an SNMP-managed device exposes for monitoring	SNMP
MPLS	Multiprotocol Label Switching	WAN forwarding technology that uses short fixed-length labels instead of IP lookups for high-speed packet switching	MPLS
MTU	Maximum Transmission Unit	Largest packet size (in bytes) that can be transmitted on a link without fragmentation; 1500 bytes for standard Ethernet	Packet Flow
MQC	Modular QoS CLI	Cisco three-step QoS framework: class-map (classify) → policy-map (act) → service-policy (apply)	QoS Overview

N ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
NAT	Network Address Translation	Router function that translates private IP addresses to a public IP (or vice versa) at the network boundary	NAT Overview
NDP	Neighbor Discovery Protocol	IPv6 protocol (RFC 4861) that replaces ARP; uses ICMPv6 messages for address resolution, router discovery, and duplicate address detection	IPv6 Neighbor Discovery
NETCONF	Network Configuration Protocol	IETF management protocol (RFC 6241) that transports XML-encoded YANG data over SSH port 830	NETCONF & RESTCONF
NIC	Network Interface Card	Hardware component that connects a device to a network; contains a burned-in MAC address	MAC Address
NMS	Network Management System	Software platform (e.g. PRTG, LibreNMS) that polls devices via SNMP and graphs performance metrics over time	SNMP
NTP	Network Time Protocol	Protocol that synchronises clocks across network devices; accurate time is essential for log correlation and certificates	NTP

O ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
OID	Object Identifier	Hierarchical numeric address in the MIB that uniquely identifies a specific SNMP-manageable variable	SNMP
OSI	Open Systems Interconnection	ISO 7-layer reference model (Physical through Application) used to describe network protocol functions	OSI Model
OSPF	Open Shortest Path First	Open-standard link-state IGP that uses Dijkstra's SPF algorithm and cost as its metric; organised into areas	OSPF Config
OUI	Organisationally Unique Identifier	First 24 bits of a MAC address assigned by IEEE to a vendor to identify the NIC manufacturer	MAC Address

P ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
PAgP	Port Aggregation Protocol	Cisco-proprietary protocol that automatically negotiates EtherChannel formation between Cisco switches	EtherChannel PAgP & LACP
PAN	Personal Area Network	Very short-range network (Bluetooth, USB) connecting personal devices around an individual	PAN
PAT	Port Address Translation	NAT variant that maps many private IP:port combinations to a single public IP with different port numbers; also called NAT overload	PAT
PDU	Protocol Data Unit	Generic term for data at each OSI layer: segment (L4), packet (L3), frame (L2), bits (L1)	OSI Model
PoE	Power over Ethernet	IEEE 802.3af/at/bt standard that delivers DC power to devices (APs, IP phones, cameras) over the same UTP cable used for data	Cable Types
PPPoE	Point-to-Point Protocol over Ethernet	Encapsulation method used by many ISPs to deliver broadband over Ethernet with authentication	WAN Technologies
PVST	Per-VLAN Spanning Tree	Cisco STP variant that runs a separate STP instance for each VLAN, enabling per-VLAN load balancing	PVST

Q ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
QoS	Quality of Service	Set of techniques (classification, marking, queuing, policing, shaping) that prioritise latency-sensitive traffic such as voice and video	QoS Overview

R ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
RADIUS	Remote Authentication Dial-In User Service	Client/server AAA protocol (UDP 1812/1813) that combines authentication and authorisation; used with 802.1X and VPNs	AAA Local & RADIUS
REST	Representational State Transfer	Architectural style for APIs using HTTP methods (GET, POST, PUT, DELETE) to manage resources identified by URIs	REST API Overview
RESTCONF	REST Configuration Protocol	IETF protocol (RFC 8040) that exposes YANG-modelled device data over HTTPS using REST semantics; supports JSON and XML	NETCONF & RESTCONF
RFC	Request for Comments	Numbered IETF document that defines Internet standards, best practices, and informational specifications	Protocols
RIP	Routing Information Protocol	Simple distance-vector IGP using hop count as its metric; maximum 15 hops; largely replaced by OSPF and EIGRP	RIP Concepts
RPC	Remote Procedure Call	NETCONF operation envelope; wraps commands such as <get-config> and <edit-config> in XML	JSON, XML & YANG
RSTP	Rapid Spanning Tree Protocol	IEEE 802.1w enhancement to STP that converges in seconds rather than ~50 seconds by using proposal/agreement handshakes	RSTP
RTT	Round-Trip Time	Time for a packet to travel from source to destination and back; measured by ping and used in network baselining	Ping

S ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
SD-WAN	Software-Defined Wide Area Network	WAN architecture that uses a centralised controller to manage and optimise traffic across multiple transport links	SD-WAN Overview
SDN	Software-Defined Networking	Architecture that separates the control plane from the data plane, centralising network intelligence in a controller	Controller-Based Networking
SLA	Service Level Agreement	Contractual or operational commitment defining acceptable thresholds for availability, latency, and loss	Network Baseline
SLAAC	Stateless Address Autoconfiguration	IPv6 mechanism allowing hosts to generate their own global unicast address using the router's advertised prefix and their EUI-64	SLAAC
SMTP	Simple Mail Transfer Protocol	Application-layer protocol for sending email between mail servers; uses TCP port 25	SMTP
SNMP	Simple Network Management Protocol	Application-layer protocol that polls MIB variables on managed devices for monitoring; SNMPv3 adds authentication and encryption	SNMP
SPAN	Switched Port Analyser	Cisco feature that mirrors traffic from one or more source ports or VLANs to a destination port connected to a packet analyser such as Wireshark	Wireshark
SPF	Shortest Path First	Dijkstra's algorithm used by OSPF and IS-IS to calculate the loop-free shortest path tree from the LSDB	OSPF Config
SSH	Secure Shell	Encrypted remote management protocol (TCP port 22) that replaces insecure Telnet for device access	SSH
SSID	Service Set Identifier	The broadcast name of a wireless network (Wi-Fi network name) that clients use to identify and associate with an AP	Wi-Fi Overview
STP	Spanning Tree Protocol	IEEE 802.1D protocol that prevents Layer 2 switching loops by placing redundant ports in blocking state	STP Overview
SVI	Switched Virtual Interface	Layer 3 logical interface on a multilayer switch representing a VLAN, used for inter-VLAN routing and management	Inter-VLAN Routing
SysLog	System Logging Protocol	Standard protocol for forwarding event messages from network devices to a centralised logging server; eight severity levels 0–7	Syslog

T ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
TACACS+	Terminal Access Controller Access-Control System Plus	Cisco AAA protocol (TCP 49) that separates authentication, authorisation, and accounting into independent transactions; encrypts the full payload	AAA Overview
TCP	Transmission Control Protocol	Connection-oriented Layer 4 protocol providing reliable, ordered, error-checked delivery via 3-way handshake and acknowledgements	Protocols
TDR	Time Domain Reflectometer	Cable testing tool that sends a signal and measures reflections to locate opens, shorts, and impedance mismatches	Cable Testing Tools
TLS	Transport Layer Security	Cryptographic protocol that provides authentication and encryption over TCP; used by HTTPS, SSH negotiation, and RESTCONF	HTTP & HTTPS
TTL	Time to Live	IP header field decremented by 1 at each router; when it reaches 0 the packet is dropped to prevent infinite routing loops	Packet Flow
TFTP	Trivial File Transfer Protocol	Simplified file transfer protocol using UDP port 69; used to back up and restore Cisco IOS images and configurations	FTP

U ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
UDP	User Datagram Protocol	Connectionless Layer 4 protocol offering low-overhead, best-effort delivery; used by DNS, DHCP, SNMP, and VoIP	Protocols
URI	Uniform Resource Identifier	String that uniquely identifies a resource; RESTCONF uses URIs to address specific YANG data nodes on a device	REST API Overview
URL	Uniform Resource Locator	Subset of URI that specifies both the resource identity and the means to access it (e.g. https://netstuts.com/ospf); every URL is a URI but not every URI is a URL	HTTP & HTTPS
UTP	Unshielded Twisted Pair	Most common copper LAN cabling; twisted wire pairs reduce crosstalk without metallic shielding; categories range from Cat 5e (1 Gbps) to Cat 8 (40 Gbps)	Cable Types

V ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
VLAN	Virtual Local Area Network	Logical segmentation of a switch into separate broadcast domains, identified by a VLAN ID (1–4094)	VLANs
VLSM	Variable-Length Subnet Masking	Subnetting method that allows different prefix lengths within the same major network to minimise address waste	Subnetting
VPN	Virtual Private Network	Encrypted tunnel that extends a private network securely over a public network such as the Internet	IPsec VPN
VRF	Virtual Routing and Forwarding	Technology that creates multiple independent routing table instances on a single router, enabling network segmentation	VRF-Lite Lab
VRRP	Virtual Router Redundancy Protocol	IEEE open-standard FHRP (RFC 5798) similar to HSRP that provides a virtual IP gateway shared between routers	VRRP & GLBP
VTP	VLAN Trunking Protocol	Cisco proprietary protocol that propagates VLAN database changes from a VTP server to all switches in the same VTP domain	VLANs

W ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
WAN	Wide Area Network	Network spanning large geographic areas — cities, countries, or the globe — typically using service-provider circuits	WAN
WLC	Wireless LAN Controller	Centralised device that manages multiple lightweight APs, handling roaming, RF management, and security policies	WLC
WPA2	Wi-Fi Protected Access 2	Wireless security standard using AES-CCMP encryption; supports Personal (PSK) and Enterprise (802.1X) modes	Wi-Fi Security
WPA3	Wi-Fi Protected Access 3	Latest wireless security standard adding SAE handshake, forward secrecy, and 192-bit encryption for Enterprise mode	Wi-Fi Security

X ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
XML	Extensible Markup Language	Tag-based structured data format; native encoding format for NETCONF and an alternative for RESTCONF	JSON, XML & YANG

Y ↑ Top

Acronym	Stands For	One-Line Definition	Full Page
YANG	Yet Another Next Generation	Data modelling language (RFC 6020 / RFC 7950) that defines the structure, types, and constraints for network device configuration schemas used with NETCONF and RESTCONF	JSON, XML & YANG

Practice Quiz – Networking Acronyms

1. What does EIGRP stand for, and what type of routing protocol is it?

A. Exterior Interior Gateway Routing Protocol — a link-state protocol B. Enhanced Interior Gateway Routing Protocol — an advanced distance-vector protocol developed by Cisco using the DUAL algorithm C. Enhanced Internet Gateway Routing Protocol — an exterior routing protocol D. Extended Interior Gateway Routing Protocol — a path-vector protocol

Correct answer is B. EIGRP stands for Enhanced Interior Gateway Routing Protocol. It is a Cisco advanced distance-vector (sometimes called "hybrid") IGP that uses the DUAL (Diffusing Update Algorithm) to guarantee loop-free paths and fast convergence. It supports unequal-cost load balancing, making it unique among IGPs. EIGRP is an Interior (not Exterior) protocol — it operates within a single autonomous system, unlike BGP which operates between autonomous systems.

2. What is the difference between NAT and PAT?

A. NAT translates MAC addresses; PAT translates IP addresses B. They are identical — PAT is just the Cisco name for NAT C. NAT translates IP addresses (one-to-one or pool); PAT (Port Address Translation) maps many private IP:port pairs to a single public IP using different port numbers — also called NAT overload D. NAT is used for IPv6; PAT is used for IPv4

Correct answer is C. NAT (Network Address Translation) broadly refers to translating IP addresses — static NAT maps one private IP to one public IP, and dynamic NAT maps a pool of private IPs to a pool of public IPs. PAT (Port Address Translation), also known as NAT overload, is the most common form used in homes and enterprises: it maps thousands of private IP:source-port combinations to a single public IP address by tracking each session via unique port numbers. PAT is a subset of NAT.

3. Which two acronyms refer to protocols used to automatically negotiate an EtherChannel between switches, and which is vendor-neutral?

A. PAgP (Cisco-proprietary) and LACP (IEEE 802.3ad — vendor-neutral) B. STP and RSTP — both vendor-neutral C. LACP (Cisco) and CDP (IEEE) — CDP is vendor-neutral D. DTP and VTP — both Cisco-proprietary

Correct answer is A. PAgP (Port Aggregation Protocol) is Cisco-proprietary and only works between Cisco switches. LACP (Link Aggregation Control Protocol) is defined in IEEE 802.3ad and works between switches from any vendor. Both negotiate the bundling of multiple physical links into a single logical EtherChannel interface for increased bandwidth and redundancy. In modern networks, LACP is preferred for its interoperability.

4. What does DSCP stand for and where is it found?

A. Differentiated Services Control Plane — found in the TCP header B. Dynamic Service Class Protocol — found in the Ethernet header C. Data Service Coding Point — found in the UDP header D. Differentiated Services Code Point — a 6-bit field in the IP header's ToS byte used to mark packets for QoS treatment at each hop

Correct answer is D. DSCP stands for Differentiated Services Code Point. It occupies the upper 6 bits of the 8-bit ToS (Type of Service) byte in the IPv4 header (called the Traffic Class byte in IPv6). Routers and switches read the DSCP value to determine the forwarding treatment — for example, EF (Expedited Forwarding, DSCP 46) is used for voice traffic and receives the lowest latency and jitter, while AF41 is used for interactive video. DSCP marking is the primary QoS classification mechanism in enterprise networks.

5. What does LSDB stand for and which routing protocol uses it?

A. Local Switching Database — used by STP to track port states B. Link State Database — used by OSPF (and IS-IS); contains all received LSAs and must be identical on all routers in an area C. Layer Switch Data Block — used by switches for MAC learning D. Link Service Data Broadcast — used by BGP for route propagation

Correct answer is B. LSDB stands for Link State Database. It is the topology table maintained by link-state routing protocols — primarily OSPF and IS-IS. Each router floods its LSAs (Link State Advertisements) to all other routers in the same area, and every router builds an identical LSDB from the received LSAs. Each router then independently runs Dijkstra's SPF (Shortest Path First) algorithm on the LSDB to build its routing table. Identical LSDBs across all routers in an area guarantee loop-free, consistent routing decisions.

6. RADIUS and TACACS+ are both AAA protocols. What is a key difference between them?

A. RADIUS uses TCP; TACACS+ uses UDP B. RADIUS is Cisco-proprietary; TACACS+ is an open standard C. RADIUS uses UDP and combines authentication and authorisation; TACACS+ uses TCP, separates all three AAA functions, and encrypts the entire payload — making it preferred for device administration D. They are functionally identical — the choice depends only on vendor preference

Correct answer is C. RADIUS (UDP ports 1812/1813) combines authentication and authorisation into a single process and encrypts only the password field. TACACS+ (TCP port 49) is Cisco-proprietary and separates authentication, authorisation, and accounting into independent transactions, giving granular per-command authorisation control. TACACS+ also encrypts the entire payload. RADIUS is typically used for network access control (802.1X, VPN users); TACACS+ is preferred for device administration (controlling which commands a network engineer can run).

7. What does SLAAC stand for and what problem does it solve?

A. Stateless Address Autoconfiguration — allows IPv6 hosts to generate their own global unicast address from the router's advertised prefix and their interface identifier, without needing a DHCPv6 server B. Static Link Address Auto-Completion — automates IPv4 static routing C. Secure Layer Address Assignment Control — a Wi-Fi security protocol D. Switch Link Aggregation and Access Control — combines LACP and port security

Correct answer is A. SLAAC (Stateless Address Autoconfiguration) is an IPv6 mechanism defined in RFC 4862 that allows a host to automatically configure a valid global unicast IPv6 address without a DHCP server. The host listens for Router Advertisement (RA) messages from a local router, extracts the advertised /64 prefix, and appends its own EUI-64 identifier (derived from the MAC address) or a random interface ID to form a complete 128-bit address. This eliminates the need for DHCPv6 in simple networks while maintaining unique addressing.

8. What does the acronym FHRP stand for, and which three protocols fall under this category?

A. Frame Header Relay Protocol — RIP, OSPF, and EIGRP B. Fast Hop Redundancy Protocol — STP, RSTP, and PVST C. Forwarding Host Routing Protocol — BGP, OSPF, and IS-IS D. First Hop Redundancy Protocol — HSRP (Cisco), VRRP (IEEE open standard), and GLBP (Cisco, adds load balancing)

Correct answer is D. FHRP stands for First Hop Redundancy Protocol — a family of protocols that provide a virtual default gateway IP address shared between two or more routers. If the active router fails, another router takes over the virtual IP transparently. The three CCNA protocols are: HSRP (Hot Standby Router Protocol — Cisco proprietary, active/ standby model), VRRP (Virtual Router Redundancy Protocol — IEEE open standard, RFC 5798, similar active/backup model), and GLBP (Gateway Load Balancing Protocol — Cisco proprietary, active/active model that load-balances across multiple routers simultaneously).

9. What does OSPF stand for, and what algorithm does it use to calculate the best path?

A. Open Shortest Path First — uses the Bellman-Ford algorithm to calculate shortest paths B. Open Shortest Path First — uses Dijkstra's SPF algorithm on an identical LSDB shared by all routers in the same area C. Open Secure Path Forwarding — uses the DUAL algorithm developed by Cisco D. Optimised Shortest Path Framework — uses a distance-vector algorithm with hop count as the metric

Correct answer is B. OSPF stands for Open Shortest Path First. It is a link-state IGP defined in RFC 2328 (OSPFv2 for IPv4) and RFC 5340 (OSPFv3 for IPv6). Every OSPF router floods LSAs throughout its area so all routers build an identical LSDB. Each router then independently runs Dijkstra's SPF algorithm on that LSDB to compute a loop-free shortest-path tree to every destination. OSPF uses cost (based on interface bandwidth) as its metric and is the most widely deployed IGP in enterprise networks.

10. What does VTP stand for, and what is the risk of running it in Server mode across your network?

A. Virtual Trunk Protocol — the only risk is increased CPU usage on switches B. VLAN Tagging Protocol — it can accidentally enable 802.1Q on all trunk links C. VLAN Trunking Protocol — a Cisco-proprietary protocol that synchronises VLAN databases; a new switch with a higher revision number can overwrite and delete all existing VLANs on every switch in the domain D. Virtual Transfer Protocol — it encrypts VLAN traffic but can cause trunk negotiation failures

Correct answer is C. VTP stands for VLAN Trunking Protocol. It is Cisco-proprietary and propagates VLAN configuration from a VTP Server to all Client switches in the same domain over trunk links. The classic danger is the revision-number attack: all switches accept the advertisement with the highest revision number — even from a newly added switch. If that switch carries a higher revision with fewer VLANs, it wipes the VLAN database on every switch, causing a network-wide outage. Best practice is VTP Transparent mode or VTP version 3.

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