A Layer 2 device that forwards frames between devices on a LAN using MAC addresses.
A switch is a Layer 2 device that learns MAC addresses by inspecting incoming frames and populates a MAC address table (also called a CAM table) to make forwarding decisions. Because each port is its own collision domain, switches eliminate the half-duplex contention that plagued hubs, allowing full-duplex operation per port. The key exam distinction is broadcast versus collision domains: a switch breaks up collision domains per port, but all ports on the same VLAN still share one broadcast domain. Configuring VLANs segments that broadcast domain, and Spanning Tree Protocol (STP) prevents the loops that form when redundant switch links exist.
A Layer 3 device that forwards packets between different networks based on IP addresses.
A router is a Layer 3 device that uses IP addresses to forward packets between distinct networks, maintaining a routing table that maps destination prefixes to outgoing interfaces or next-hop addresses. Unlike a switch, which forwards frames within a single broadcast domain using MAC addresses, a router creates a boundary between broadcast domains, stopping broadcasts from propagating across segments. On the N10-009 exam, distinguish static routing, where an admin manually enters routes, from dynamic protocols such as OSPF or EIGRP, which automatically exchange routing information. Also contrast routers with Layer 3 switches, which route in hardware optimized for high-speed intra-network traffic rather than WAN edge connections.
A Virtual LAN that logically segments a switch into separate broadcast domains.
A VLAN (Virtual LAN) partitions a physical switch into multiple logical broadcast domains using IEEE 802.1Q tagging, so frames carry a 12-bit VLAN ID (1–4094 usable) as they traverse trunk links between switches. Devices in different VLANs cannot communicate directly even if they share the same physical hardware, which contains broadcast storms and confines sensitive traffic — such as voice or management traffic — to its own segment.
The critical exam distinction is that VLANs operate at Layer 2 and provide isolation, but routing between VLANs still requires a Layer 3 device. A common trap: adding a host to a different VLAN on the same switch does not automatically grant it network access — the router or Layer 3 switch must have a corresponding interface or subinterface configured for that VLAN.
Carrying traffic for multiple VLANs over a single switch link using 802.1Q tagging.
Trunking uses IEEE 802.1Q to insert a 4-byte tag into each Ethernet frame, identifying its VLAN, so one physical link between two switches — or a switch and a router — can carry many VLANs at once. The native VLAN is the exception: its frames travel untagged, so both ends must share the same native VLAN ID or traffic is misassigned. Do not confuse a trunk with an access port, which belongs to one VLAN and strips tagging. VLAN 1 is the default native VLAN on Cisco-style switches, and leaving it so is a known security concern.
A protocol that prevents switching loops by blocking redundant paths while keeping a backup ready.
Spanning Tree Protocol (STP), defined in IEEE 802.1D, prevents Layer 2 switching loops by electing a single root bridge and placing redundant switch ports into a blocking state. Every non-root switch picks a root port (lowest-cost path to the root), each segment elects a designated port, and all other ports block. Classic STP converges in roughly 30 to 50 seconds, moving through Listening and Learning states before Forwarding. Rapid STP (RSTP, 802.1w) adds Alternate and Backup port roles and converges in seconds by negotiating transitions. Network+ expects you to know both versions plus their port states and roles.
Manually configured routes that do not change unless an administrator updates them.
Static routing uses manually entered routing-table entries to forward packets along fixed, administrator-defined paths. Since the table never updates itself, the router uses no bandwidth on protocol messages and resists route injection. The key exam distinction is against dynamic protocols such as OSPF or EIGRP, which detect link failures and recalculate paths automatically. A static route stays until manually removed, so a failed link can create a black hole where packets are silently dropped. It therefore suits stub networks with one exit point, or a default route of last resort (0.0.0.0/0) sending unmatched traffic upstream.
Routing in which protocols automatically learn and update routes as the network changes.
Dynamic routing protocols let routers automatically discover neighbors, exchange reachability information, and recalculate best paths whenever the topology changes. Examples on N10-009 include OSPF (a link-state protocol that builds a full topology map) and BGP (used between autonomous systems on the internet). Unlike static routing, it adapts to link failures without administrator intervention, making it the standard choice for larger networks. The key exam contrast is convergence: link-state protocols like OSPF reconverge faster than older distance-vector protocols, which propagate changes hop by hop. Pair “self-healing” or “automatic failover” with a dynamic protocol, not a static route.
Open Shortest Path First — a link-state interior gateway protocol that computes shortest paths by cost.
OSPF (Open Shortest Path First) is a link-state interior gateway protocol. Each router floods link-state advertisements through an autonomous system, then runs Dijkstra’s Shortest Path First algorithm on the topology database to compute loop-free routes. Because every router holds an identical map, OSPF reconverges much faster than distance-vector protocols like RIP, which rely on hop count and periodic updates. For the exam, OSPF’s metric is cost (derived from bandwidth), not hop count. Both OSPF and EIGRP are classless IGPs, but EIGRP is Cisco-proprietary, while OSPF is an open standard — RFC 2328 for OSPFv2, RFC 5340 for OSPFv3 (IPv6).
Border Gateway Protocol — the path-vector protocol that routes traffic between autonomous systems on the internet.
Border Gateway Protocol (BGP) is the Exterior Gateway Protocol (EGP) that exchanges routing information between autonomous systems (ASes) — the independently administered networks that make up the internet. Unlike interior protocols such as OSPF or EIGRP, which optimize for shortest path within one organization, BGP is a path-vector protocol that selects routes using policy attributes: AS-path length, origin type, local preference, and MED. It runs over TCP port 179 with manually configured peers. eBGP connects separate ASes, while iBGP carries those routes within an AS. Recognize BGP as internet-scale routing, not a typical enterprise LAN protocol.
Enhanced Interior Gateway Routing Protocol — a Cisco advanced distance-vector protocol with fast convergence.
EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco-proprietary advanced distance-vector protocol that uses the Diffusing Update Algorithm (DUAL) to calculate loop-free paths and keep backup routes in a topology table, enabling near-instant failover when a primary path fails. It sends partial, bounded updates rather than full routing-table broadcasts, conserving bandwidth versus RIP. The exam often contrasts EIGRP with OSPF: both are interior gateway protocols with fast convergence, but OSPF is an open standard using link-state flooding, while EIGRP is Cisco-only and forms neighbor relationships over multicast 224.0.0.10. On mixed-vendor networks, choose OSPF.