Memory hook: Match medium, distance, power and failure domain.
Must remember
Copper twisted pair commonly uses RJ45 connectors; telephone cabling uses smaller RJ11. Fiber connectors include LC, SC, ST and multifiber MPO. Coaxial systems may use F-type or BNC. Connector fit alone does not prove the correct medium, wavelength, speed or polarity.
Single-mode fiber supports long-distance optical paths with suitable optics; multimode fiber serves shorter links under its own distance/speed limits. DAC cables connect nearby compatible equipment economically. Match transceiver form factor, wavelength, fiber type and supported standard at both ends. Dirty fiber, reversed transmit/receive pairs, excessive bend radius, bad termination and electromagnetic interference have distinct symptoms.
PoE supplies power over compatible Ethernet links. Check per-port standard/class and the switch's total power budget; enough data connectivity does not prove enough power for an AP or phone. Racks need appropriate airflow, grounding, cable management, labeling, temperature and humidity. UPS provides short-term continuity; generators and diverse feeds address longer/different failures.
Cloud networking includes virtual networks/subnets, security groups/policies, gateways, load balancers and virtual appliances. IaaS, PaaS and SaaS shift operational responsibility. NFV implements network functions in software; SDN programs/control-separates networking. SD-WAN steers overlay paths using policy; SASE combines distributed access and security capabilities.
Hybrid connectivity joins cloud and on-premises environments; overlapping CIDRs complicate routing. VPN encryption and private circuits solve different transport requirements. Elasticity changes resources with demand; scalability is the ability to grow. Cloud data-transfer and public-address costs can dominate an apparently cheap design.
Document physical and logical diagrams, rack elevation, cable maps, circuits and IP allocations. Label both ends so future troubleshooting starts with evidence instead of guesswork.
Choose under exam pressure
| Requirement | Choice and reason |
|---|---|
| Long optical distance | Compatible single-mode optics/fiber and verified link budget. |
| AP reboots under load | Check PoE negotiation/budget and physical power conditions. |
| Hybrid routing conflict | Inspect overlapping address ranges before adding routes. |
Traps
- Two fiber connectors mating does not guarantee compatible optics.
- A private circuit is not automatically encrypted.
Active recall
1. Why check both per-port and total PoE capacity?
A port may support a device while the whole switch lacks remaining power budget.
2. Single-mode versus multimode?
They use different optical propagation/media characteristics and supported distances/optics.
3. What does SD-WAN add?
Policy-based management/selection of WAN paths through an overlay architecture.
4. Why are overlapping cloud and on-premises ranges troublesome?
A destination may not be uniquely routable without redesign or translation.
5. What documentation helps trace a physical fault?
Accurate cable labels/maps, rack diagrams and device/port inventory.