• Ethernet framing and PHY
• Switching and MAC learning
• Loop prevention: STP/RSTP/MST
• VLANs and trunking (802.1Q)
• Link aggregation (LACP), MLAG
• Design tips and troubleshooting
• Exercises

• Frame fields: dest/src MAC, EtherType/length, payload, FCS (CRC32).
• Minimum/maximum sizes (64–1518 bytes without VLAN tag; jumbo frames optional).
• PHY/Media: copper (1000BASE-T), fiber, auto-negotiation, duplex.

[DA][SA][EthType][Payload][FCS]

• Bridges learn source MAC → port; forward/filter based on destination MAC.
• Flood unknown unicast/broadcast; aging to prune stale entries.
• Multicast handling (IGMP/MLD snooping).

CAM/FIB: MAC 00:11:22:33:44:55 → port 5 (VLAN 10)

• Spanning Tree builds a loop-free tree: root election, port roles, states.
• RSTP accelerates convergence; MST groups VLANs into instances.
• Tuning: portfast/edge, BPDU guard, root guard, uplinkfast.

Root Bridge → Designated/Root/Alternate ports; BPDUs maintain tree

• 802.1Q adds a 4-byte tag (TPID 0x8100) with VLAN ID and PCP priority.
• Access vs trunk ports; native VLAN; QinQ (802.1ad) for provider stacking.
• Inter-VLAN routing via L3 SVI or router-on-a-stick.

[DA][SA][0x8100][TCI: VID, PCP, DEI][EthType][Payload][FCS]

• 802.1AX/LACP bundles links for bandwidth and redundancy.
• Hashing choices (L2/L3/L4 fields) affect flow distribution.
• MLAG provides multi-chassis LAG using vendor-specific protocols.

• Use a clear L2 domain design; avoid accidental loops; monitor STP events.
• Document VLAN plans; avoid native VLAN mismatches; secure trunks.
• Tools: LLDP/CDP, spanning-tree show, MAC table, packet captures.

1. Draw a small L2 topology and simulate STP root election and port roles.
2. Configure VLAN trunking and verify tagging/untagging with a packet capture.
3. Create an LACP bundle on a lab switch/router and test failover behavior.