Ethernet and Switching

Switch Learning and Forwarding

Learn how a Layer 2 switch learns MAC addresses, chooses forwarding paths, handles unknown destinations, and manages table entries over time.

Intermediate12 min read
Ethernet and Switching lessonNetworkingPractice

UNTIMED COACHING

Practice before the pressure

Use feedback to correct the model, not merely memorize an option position.

GUIDED PRACTICE

Practice the lesson questions

Answer normal lesson questions without a timer. Every answer includes an explanation, and incorrect answers can be tried again before continuing.

CONCEPT MODELS

See the lesson as a system

Use these visual guides to connect the key ideas before answering the questions.

How a Switch Learns LocationsA switch records source locations and uses the table to guide later forwarding.
How a Switch Learns LocationsFrames enter a switch; source information updates a table containing MAC address, port, and VLAN relationships.
Incoming frameCarries source and destination MACs
Source MACIdentifies the frame sender
MAC address tableMaps MAC addresses to ports
Port and VLANRecords sender location and VLAN
Separating Learning From ForwardingSource inspection updates knowledge; destination lookup determines frame treatment.
Separating Learning From ForwardingA received frame branches into source learning and destination lookup before directed forwarding or same VLAN flooding.
Received frameEnters through one switch port
Learn sourceAdd or revise observed location
Look up destinationSearch the MAC address table
Known destinationUse the matching port and VLAN
Table Maintenance And PressureAging removes inactive entries, while limits and flooding can broaden forwarding.
Table Maintenance And PressureInactive entries age out; learned MAC pressure and deliberate unique sources can lead to unknown unicast flooding.
Learned entriesRepresent observed source MACs
AgingRemoves inactive associations
Learned MAC limitLimits additional learned addresses
Same VLAN floodingSends unknown unicast to VLAN ports