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L4.3 — Ethernet by Kirk Martinez. This lecture dives deeper into Ethernet — the protocol that underpins virtually all modern local area networking. It covers the Ethernet frame structure in detail (preamble, octets, CRC, inter-frame gap, jumbo frames), MAC addresses and vendor prefixes, how to read link-layer stats with ip link, the Address Resolution Protocol (ARP) and how IPv4 machines discover each other's MAC addresses, ARP caching, ARP spoofing attacks, gratuitous ARP, IPv6 Neighbour Discovery Protocol (NDP) as the modern replacement for ARP, broadcast domains and subnetting, network masks and default routers, IPv4 vs IPv6 router discovery, campus and building network design using switches and high-speed fibre, bonding, home networks, spanning tree algorithm, and VLANs with QoS priorities.

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📋 At a Glance

• [ ] Know that Wi-Fi still uses Ethernet frames — Ethernet is everywhere at the edge of the network
• [ ] Understand the Ethernet frame structure field by field: preamble, dest MAC, src MAC, optional tags, payload, CRC, inter-frame gap
• [ ] Know that networking people call bytes "octets" — each MAC address is 6 octets
• [ ] Explain the purpose of the preamble (synchronisation — tells the receiver a frame is arriving)
• [ ] Know that the standard payload is up to 1500 bytes; jumbo frames allow larger payloads (special setting)
• [ ] Know that CRC (4 bytes) at the end allows the receiver to detect corrupted frames
• [ ] Understand inter-frame gap (12 bytes of silence between frames for resynchronisation)
• [ ] Explain how MAC address vendor prefixes work — manufacturers manage their own MAC address blocks
• [ ] Use ip link / ip -s link to view MAC addresses, broadcast address, and link-layer statistics
• [ ] Know the loopback interface (127.0.0.1) — always present, used for local inter-process communication
• [ ] Explain ARP (Address Resolution Protocol) — how IPv4 maps IP addresses to MAC addresses
• [ ] Describe the ARP request/reply cycle: broadcast "who has IP X?", unicast reply "I do, here's my MAC"
• [ ] Know that ARP only resolves local (LAN) addresses — never used to find internet IPs
• [ ] Know the difference: unicast (one-to-one), broadcast (one-to-all-on-LAN), multicast (one-to-subscribers), anycast (one-to-nearest)
• [ ] Explain the ARP packet format: sender MAC, sender IP, target MAC (blank in request), target IP
• [ ] Know that ARP results are cached (dynamic — can expire or change)
• [ ] Explain ARP spoofing — an attacker replies with a fake MAC to intercept or redirect traffic