2.3 Link Aggregation, Power over Ethernet (PoE) & Port Mirroring
Focuses on LACP link bundling, Power over Ethernet wattage classes, and non-intrusive traffic monitoring with SPAN.
🎯 Key CompTIA Network+ Exam Takeaways
- LACP (802.3ad/802.1ax) bundles physical links; at least one side must be in Active mode to establish a dynamic port channel.
- PoE standards: 802.3af (15.4W), 802.3at PoE+ (30W), and 802.3bt PoE++ (60W Type 3, 90W Type 4).
- SPAN (Port Mirroring) duplicates ingress/egress frames to an analysis port without disrupting production traffic.
Link aggregation bundles multiple physical Ethernet interfaces into a single high-bandwidth logical trunk, providing both bandwidth aggregation and link-level failover. The open standard Link Aggregation Control Protocol (LACP) actively exchanges control packets to monitor link health.
Power over Ethernet (PoE) transmits direct current power alongside data over standard twisted-pair copper cables. High-draw devices like motorized PTZ surveillance cameras, multi-radio Wi-Fi 6 access points, and video endpoints require 802.3bt (PoE++), which delivers up to 60W or 90W.
Switched Port Analyzer (SPAN) duplicates frames from specified source ports, VLANs, or port channels to a dedicated destination port connected to an IDS/IPS or packet capture appliance.
⚠️ Common Pearson VUE Exam Traps
- Configuring both ends of an LACP bundle as Passive, which results in negotiation deadlock where no channel forms.
- Deploying 802.3at (PoE+) for high-power PTZ cameras or digital signage requiring over 30 Watts.
Knowledge Checkpoint
An IT department is deploying motorized pan-tilt-zoom (PTZ) IP surveillance cameras with integrated heaters that consume 55 Watts of continuous power. Which PoE standard must the access switch ports support to power these devices over standard Cat 6 cabling?