L2 — Data Link

Ethernet frames, MAC addresses, switching. Broadcast domains live here.

What lives at L2

• Ethernet
• VLAN (802.1Q)
• 802.1X — port authentication
• Spanning Tree (STP/RSTP/MSTP)
• LACP / port channels
• MACsec
• ARP (strictly bridges L2/L3)

Key identifiers

• MAC address (48-bit)
• VLAN ID (12-bit)