What are the common Data Link protocols used on LANs and WANs?

LANs use Ethernet and 802.11 wireless; WANs use PPP, HDLC, and Frame-Relay.

The logical topology and physical media determine the data link protocol used:

LAN Protocols:

• Ethernet - Most common LAN protocol
• 802.11 Wireless - Wi-Fi

WAN Protocols:

• PPP (Point-to-Point Protocol)
• HDLC (High-Level Data Link Control)
• Frame-Relay

Key point: Each protocol performs media access control for specified logical topologies.

Go deeper:

• Data link layer (Wikipedia) — lists both groups explicitly: LAN (Ethernet, 802.11) using MAC/LLC; WAN (Frame Relay, HDLC, PPP).
• Point-to-Point Protocol (Wikipedia) — the representative WAN protocol, contrasting the LAN examples.