This networking glossary explains essential terms for CCNA study, technical interviews, and day-to-day network troubleshooting. Use it as a quick reference, then follow the linked guides for deeper explanations and examples.
Network Hardware
Network Interface Card (NIC)
A NIC connects a host to a wired or wireless network. It operates primarily at the physical and data-link layers and uses a hardware address for local Ethernet communication.
Repeater
A repeater regenerates a weakened signal so it can travel farther. It does not examine IP addresses or make forwarding decisions.
Hub
An Ethernet hub repeats incoming bits out every other port. All connected devices share one collision domain, which is why hubs have largely been replaced by switches.
Bridge
A bridge learns MAC addresses and forwards frames between LAN segments. A modern Ethernet switch performs the same basic function across many ports.
Switch
A switch learns source MAC addresses, builds a MAC address table, and forwards frames to the appropriate port. Managed switches can also support VLANs, trunks, spanning tree, link aggregation, security, and monitoring.
Router
A router forwards packets between IP networks. It selects a path using connected routes, static routes, or routes learned through routing protocols.
Addressing and Network Services
MAC Address
A MAC address identifies a network interface for local data-link communication. Ethernet switches use destination MAC addresses to make forwarding decisions.
IP Address
An IPv4 or IPv6 address identifies an interface at the network layer. Its prefix separates the network portion from the host or interface portion.
Subnet Mask and Prefix Length
A subnet mask, such as 255.255.255.0, or a prefix length, such as /24, defines how many address bits represent the network.
Default Gateway
A host sends traffic for remote networks to its default gateway, normally a router interface or virtual gateway address on the local subnet.
ARP
Address Resolution Protocol maps an IPv4 address to a MAC address on the local network. IPv6 uses Neighbor Discovery instead.
DNS
The Domain Name System translates names into IP addresses and stores other records used by applications and network services. Read the DNS guide for more detail.
DHCP
Dynamic Host Configuration Protocol assigns addressing information such as an IP address, prefix, default gateway, and DNS servers to clients.
Switching Terms
VLAN
A virtual LAN creates a logical Layer 2 broadcast domain on a switch. Devices in different VLANs require Layer 3 routing to communicate.
Access Port
An access port normally carries traffic for one VLAN and connects an endpoint such as a computer, phone, printer, or server.
Trunk Port
A trunk carries traffic for multiple VLANs, commonly using IEEE 802.1Q tags between switches, routers, firewalls, or virtualization hosts.
Spanning Tree Protocol
STP prevents Layer 2 loops by electing a root bridge and placing redundant paths into forwarding or blocking roles.
EtherChannel
EtherChannel combines compatible physical links into one logical link to increase capacity and provide redundancy. LACP is the standards-based negotiation protocol.
Routing Terms
Routing Table
A routing table contains destination prefixes and information used to select a next hop or outgoing interface.
Static Route
A static route is manually configured. It is predictable and simple but does not automatically learn a new path when the topology changes.
RIP
Routing Information Protocol is a distance-vector protocol that uses hop count as its metric. Compare versions in the RIPv1 vs RIPv2 guide.
OSPF
Open Shortest Path First is a link-state interior gateway protocol. Routers build a topology database and calculate shortest paths within an OSPF domain.
BGP
Border Gateway Protocol exchanges reachability information between autonomous systems and is the principal interdomain routing protocol of the internet.
Administrative Distance
Administrative distance ranks the trustworthiness of routes learned from different sources on a Cisco device. The lowest value is preferred when routes have the same prefix length.
Routing Metric
A metric lets a routing protocol compare multiple paths it has learned. Examples include hop count, cost, bandwidth, delay, or a composite calculation.
Traffic Delivery
Unicast
Unicast is one-to-one delivery between a sender and a receiver.
Broadcast
Broadcast is one-to-all delivery within an IPv4 broadcast domain.
Multicast
Multicast is one-to-many delivery to receivers that join a group. See IP multicast explained.
Security and Troubleshooting
ACL
An access control list matches traffic using criteria such as protocol, address, and port, then permits or denies it according to ordered rules.
Firewall
A firewall enforces security policy between network zones. Stateful firewalls track connection state and can make decisions using application and threat context.
IDS and IPS
An IDS detects and alerts on suspicious activity. An IPS is normally inline and can block malicious traffic. Read our IDS vs IPS guide.
Ping
Ping uses ICMP echo messages to test IP reachability and measure round-trip response time. A failed ping does not always prove a host is down because ICMP may be filtered.
Traceroute
Traceroute shows the Layer 3 hops toward a destination by sending probes with increasing time-to-live or hop-limit values.
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