Part 1 · 1 chapters · ~8 min

Ethernet and Switching

Frames and MAC addresses, the MTU, ARP and its cache, learning switches and flooding, broadcast domains and VLANs, spanning tree, Wi-Fi differences, and how cloud VPCs virtualise all of it.

3

Frames, ARP and switches

code
ip link show                 # interfaces, MAC addresses, MTU
arp -a                       # the ARP cache (ip neigh on Linux)
ping -D -s 1472 10.0.0.9     # 1472 + 8 ICMP + 20 IP = 1500: tests the path MTU (-D sets don't fragment on macOS; -M do on Linux)
ETHERNET AND SWITCHING
frames, MAC addresses, learning switches and ARP
host A10.0.0.5, MAC aa:..switchMAC tablehost B10.0.0.9, MAC bb:..ARPwho has 10.0.0.9?VLANsseparate broadcast domains
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frames
Ethernet carries frames with source and destination MAC addresses (48-bit, burned into or assigned to network interfaces), a type field and a checksum, up to 1,500 bytes of payload by default (the MTU).
frames with MAC addresses, MTU 1,500jumbo frames up to ~9,000 inside data centres