Network Infrastructure

What this unit covers

The topics below follow the published Networking course framework for Unit 2. Networking publishes no per-unit weighting, so there is no percentage to chase here.

Lessons in this unit

• Switching and VLANs18 min · 3 objectivesExplain Layer 2 forwarding and logical segmentation · Apply the idea to evidence from a realistic technology scenario · Justify a decision using security, reliability, cost, and user impact
• Routing and Path Selection18 min · 3 objectivesExplain routing tables, next hops, and path decisions · Apply the idea to evidence from a realistic technology scenario · Justify a decision using security, reliability, cost, and user impact
• Wireless Infrastructure and Coverage18 min · 3 objectivesExplain wireless design, channels, roaming, and capacity · Apply the idea to evidence from a realistic technology scenario · Justify a decision using security, reliability, cost, and user impact

Every term in Unit 2

All 40 terms we publish for Network Infrastructure, with definitions. Reading them through is the fastest way to find the ones you cannot define — then drill those in cram mode until you can produce them without the prompt.

VLAN

Logically splits one physical switch into separate broadcast domains. Inter-VLAN traffic must cross a router, which is where access control can be enforced.

NAT

Rewrites private addresses to a public one at the boundary, letting many internal hosts share one public address. It also incidentally hides internal structure.

MAC address table

The switch's record of which MAC address is reachable through which port, learned from the source address of arriving frames.

Flooding an unknown frame

When a switch has no table entry for a destination, it sends the frame out every port except the one it arrived on — then learns from the reply.

Access port vs trunk port

An access port belongs to one VLAN and carries untagged traffic to an end device. A trunk carries several VLANs between switches, tagging each frame.

802.1Q tagging

Inserts a VLAN identifier into the Ethernet frame so a trunk can carry many VLANs on one link and the far end can separate them again.

Inter-VLAN routing

A router or layer 3 switch moving traffic between VLANs. Without it VLANs are isolated, which is often exactly the point.

Spanning Tree Protocol

Detects redundant switch paths and blocks all but one, preventing loops. Without it, a single loop floods broadcasts until the network stops.

Broadcast storm

Broadcast frames circulating a switching loop endlessly, consuming all capacity. The failure STP exists to prevent.

Link aggregation

Bonding several physical links into one logical link for more throughput and redundancy.

Power over Ethernet

Supplies power over the data cable, so access points, cameras and phones need no separate outlet. Power budget becomes a switch specification.

Port security

Restricting which MAC addresses may use a switch port, and what happens on violation. A layer 2 control against unauthorized devices.

Routing table

The list of known destination networks and the next hop toward each. A router consults it for every packet.

Longest prefix match

When several routes could carry a packet, the most specific one wins — a /24 beats a /16 for an address inside both.

Default route

The 0.0.0.0/0 entry used when nothing more specific matches. On most networks it points at the internet.

Static vs dynamic routing

Static routes are configured by hand: predictable and unresponsive to failure. Dynamic protocols share reachability automatically and adapt when a link drops.

Routing metric

The cost a protocol uses to compare routes — hop count, bandwidth, delay. Different protocols choose differently, so "shortest" depends on who is measuring.

RIP

A distance-vector protocol using hop count, capped at 15 hops. Simple, slow to converge, and largely historical.

OSPF

A link-state interior protocol using cost derived from bandwidth. Each router builds a full map of the area and computes its own shortest paths, so convergence is fast.

BGP

The exterior protocol that routes between autonomous systems and holds the internet together. Chooses on policy as much as on distance.

Interior vs exterior gateway protocol

Interior protocols route inside one administrative domain; exterior protocols route between them. OSPF is interior, BGP exterior.

Convergence

The time after a change until every router agrees on the topology again. Traffic can loop or blackhole during it.

PAT (NAT overload)

The common form of NAT, using port numbers to distinguish many internal sessions behind a single public address.

Port forwarding

A NAT rule sending inbound traffic on a given port to a specific internal host, so an internal service can be reached from outside.

802.11 standards

Wi-Fi generations differ in band, modulation and throughput: 802.11n added dual band, 802.11ac pushed 5 GHz throughput, 802.11ax (Wi-Fi 6) improved performance in dense environments.

2.4 GHz vs 5 GHz

2.4 GHz travels further and through more walls, carries less, and is crowded. 5 GHz is faster and shorter-ranged. 6 GHz adds more clean spectrum where supported.

Non-overlapping channels

In 2.4 GHz only channels 1, 6 and 11 do not overlap. Neighboring access points on adjacent channels interfere with each other and with everyone else.

SSID

The network name a wireless network advertises. Several access points share one SSID to let clients roam.

Wireless roaming

A client moving between access points on the same SSID without losing its session. Requires overlapping coverage and consistent configuration.

Site survey and heat map

Measuring actual signal coverage before and after deployment. The way access-point placement stops being guesswork.

Interference and attenuation

Microwaves, cordless phones and other networks interfere; walls, floors and distance attenuate. Both reduce usable throughput without breaking the link.

Cloud service models

IaaS provides virtual infrastructure, PaaS a managed platform to deploy onto, SaaS finished software. Each moves more responsibility to the provider.

Cloud deployment models

Public, private, hybrid and community — who owns and who may use the infrastructure, independently of the service model.

Edge computing

Processing data near where it is produced rather than shipping it to a central cloud. Cuts latency and bandwidth, and suits sensors and video.

Software-defined networking

Separates the control plane deciding where traffic goes from the data plane forwarding it, so behavior is programmable centrally.

Virtualization

Running many logical machines or networks on shared physical hardware. The reason a data center topology no longer matches its cabling.

Network topologies

Star, mesh, bus and ring describe how devices interconnect. Star dominates in practice; mesh appears where redundancy justifies the cost.

Redundancy vs fault tolerance

Redundancy is having spare capacity or paths; fault tolerance is continuing to work when something fails. Redundancy makes fault tolerance possible and does not guarantee it.

Quality of service (QoS)

Prioritizing some traffic over other traffic when capacity is short. Voice and video need it; bulk file transfer is what gets deprioritized.

Structured cabling and patch panels

Terminating runs in a documented, labeled panel rather than device to device. Makes moves and changes routine instead of archaeological.

What examiners penalize here

• For a scenario about **Layer 2 forwarding and logical segmentation**, identify the decisive evidence before naming a response. A defensible conclusion here is: VLANs provide segmentation, but policy at the routed boundary determines what communication is allowed.
• For a scenario about **routing tables, next hops, and path decisions**, identify the decisive evidence before naming a response. A defensible conclusion here is: The router forwards through gateway B using the /24 route.
• For a scenario about **wireless design, channels, roaming, and capacity**, identify the decisive evidence before naming a response. A defensible conclusion here is: Treat this as a capacity and airtime problem, then validate the redesign under realistic load.

Practice Networking

Our practice bank is drawn from across the whole course rather than filtered to one unit, which is closer to how the exam asks anyway — it will not tell you which unit a question is testing.

Questions about this unit

All 5 units of AP Networking

1. Unit 1 · Network Foundations
2. Unit 2 · Network Infrastructure
3. Unit 3 · Network Services
4. Unit 4 · Network Operations
5. Unit 5 · Network Security