Stage 2 · Lesson 1 of 8
How a switch learns and forwards
A connects devices in one local network and forwards by . It learns by reading the source MAC of every frame and noting the port it came in on, building its . For each frame it then looks up the destination MAC: if it is known, the frame goes out of that one port; if it is unknown, or a , the frame is flooded out of every other port in the same VLAN.
Entries age out after a few minutes of silence. Reading the table with show mac address-table is how you find which port a device is plugged into, a question behind many access-layer tickets.
Common trapexpecting a device to appear in the table before it has sent anything: switches learn only from traffic.
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Resources for this stage
Start with· follow one of these
- VideoFreeJeremy's IT Lab: CCNA 200-301 Complete Course
Jeremy's IT Lab · Beginner
The VLAN, spanning tree and EtherChannel days, each with a Packet Tracer lab to do straight after
- PlatformFreeCisco Networking Academy
Cisco · Beginner
The switching and VLAN modules of the CCNA courses, if your university or institute runs them