Junior Network Administrator key terms

A seven-layer reference framework describing how data moves from an application on one host to an application on another, with each layer handling a distinct job such as addressing, routing, or framing.

The four-layer stack actually used on the Internet: network access, internet, transport, and application. It maps loosely onto the OSI layers but merges several of them together.

The process of wrapping data with a new header at each layer as it moves down the stack, so a segment gains an IP header to become a packet and then a frame header before transmission.

Protocol data unit: the name for data at a given layer, such as segment at transport, packet at network, and frame at data link. Naming the PDU clarifies which headers are present.

Maximum transmission unit, the largest payload a link will carry in one frame, typically 1500 bytes on Ethernet. Oversized packets must be fragmented or dropped, which breaks some applications.

Splitting an IP packet into smaller pieces so it fits a link with a smaller MTU. Reassembly happens at the destination, and a single lost fragment discards the whole original packet.

A 32-bit value of contiguous ones followed by zeros that tells a host which portion of an IPv4 address identifies the network and which portion identifies the host.

Writing a network as an address followed by a slash and the count of network bits, such as 192.168.10.0/24. The prefix length replaces the dotted-decimal mask and allows arbitrary boundaries.

The address formed by setting all host bits to zero, which names the subnet itself and cannot be assigned to a device. It is the first address in the range.

The address with all host bits set to one, used to reach every host on the local subnet. It is the last address in the range and cannot be assigned to a single device.

The router address a host sends traffic to when the destination is outside its own subnet. Without a correct gateway, a host can reach local peers but nothing beyond them.

Variable length subnet masking: dividing a block into subnets of different sizes so each segment gets only the addresses it needs, conserving space on point-to-point and small links.

A list of known destinations with the next hop or interface used to reach each one. The router picks the most specific matching entry, using prefix length as the tiebreaker.

A route an administrator configures by hand rather than learning from a routing protocol. It is predictable and simple but does not adapt automatically when a link fails.

A preference value a router uses to rank routes to the same destination learned from different sources. Lower values win, so connected routes beat static routes, which usually beat dynamic protocols.

A Layer 2 device that forwards frames between ports based on learned MAC addresses. It creates separate collision domains per port and supports VLANs for logical segmentation.

A Layer 3 device that forwards packets between different IP networks, choosing a path from its routing table and rewriting link-layer headers at each hop.

A wireless device that bridges Wi-Fi clients onto a wired network, advertising a service set identifier and handling association, authentication, and encryption for connected stations.

The arrangement of links and nodes in a network, such as star, mesh, or hub-and-spoke. Physical topology describes cabling while logical topology describes how traffic actually flows.

Unshielded twisted pair copper cabling whose four pairs are twisted to reduce interference. Common categories support 1 Gbps to 100 m, and higher categories support 10 Gbps over shorter runs.

Cabling that carries data as pulses of light through glass or plastic strands. It supports far longer distances and higher bandwidth than copper and is immune to electromagnetic interference.

The rating that defines a twisted-pair cable's supported frequency and data rate, such as Cat5e, Cat6, or Cat6a. The rating must match the speed the connected equipment expects.

A pluggable module that converts signals between a switch port and a specific media type, such as copper or fiber. Matching the module to the cable and distance is a common deployment check.

A switch's mapping of learned source MAC addresses to the ports they arrived on. Unknown destinations are flooded to all ports in the VLAN until the table learns the location.

A logical grouping of switch ports that behaves as its own broadcast domain regardless of physical location. Traffic between VLANs requires a Layer 3 device to route it.

A switch link that carries frames for multiple VLANs at once, tagging each one so the far end knows which VLAN it belongs to. Typically connects switches or a switch to a router.

A switch port assigned to a single VLAN that sends untagged frames to an end device such as a workstation or printer. The device is unaware of any VLAN tagging.

The set of devices that receive a broadcast frame sent by any one of them. Routers and VLAN boundaries stop broadcasts, keeping broadcast traffic from spreading network-wide.

The name a wireless network advertises so clients can find and join it. Multiple access points can share one SSID to let clients roam between them.

A wireless client moving its association from one access point to another with the same SSID while keeping its session. Overlapping coverage and matched security settings make it work smoothly.

Interference that occurs when nearby access points use overlapping frequency ranges, forcing them to share airtime. Choosing non-overlapping channels in the same band avoids the slowdown.

A protocol that automatically supplies clients with an IP address, subnet mask, default gateway, and DNS servers from a configured pool, removing the need for manual configuration.

The time-limited assignment of an address to a client, which renews before expiry and returns to the pool if the client disappears. Short leases suit guest networks; long leases reduce churn.

The system that resolves human-readable names into IP addresses through a hierarchy of servers. Queries walk from root to top-level domain to authoritative server unless a cache answers first.

Network address translation rewrites private source addresses to a public address as traffic leaves a network, tracking the mapping so replies return to the right internal host.

Port address translation, a NAT variant that lets many internal hosts share one public address by tracking each connection with a unique source port number.

A protocol that synchronizes device clocks to a reference time source over the network. Accurate time matters for log correlation, certificate validation, and authentication protocols.

The 169.254.0.0/16 range a Windows host self-assigns when no DHCP server answers. Seeing such an address on a client is a strong hint that DHCP is unreachable.

A standard for sending log messages from network devices to a central collector at a chosen severity level. Central logging preserves evidence and makes correlation across devices possible.

A protocol for reading and polling device statistics and status through structured object identifiers. Traps push alerts to a manager, while polling pulls counters on a schedule.

A recorded snapshot of normal performance and traffic patterns used as a comparison point. Without it, an administrator cannot tell whether current behavior is abnormal or expected.

A device or host feature that permits or blocks traffic according to rules about addresses, ports, and protocols. Stateful firewalls track connections so return traffic is allowed automatically.

An ordered list of permit and deny statements applied to interfaces or traffic flows. The first matching entry decides the outcome, so placement and order determine the result.

A tool that sends ICMP echo requests to test whether a host is reachable and to measure round-trip time. A failed ping may mean filtering rather than a dead host.

A tool that reveals the routers along a path by sending packets with increasing hop limits and collecting the replies. It shows where traffic stops or slows.

A handheld tool that checks continuity, pinout, and sometimes length or faults on copper links. It confirms wiring problems before time is spent investigating higher layers.

A record of what was altered on a network, when, by whom, and why, plus the rollback plan. It shortens future troubleshooting by explaining why the configuration looks as it does.

A labeled drawing of devices, links, addresses, and VLANs that reflects the current design. Accurate diagrams speed fault isolation and are essential during outages and handovers.