A day in the life… ARP (before DNS, before HTTP)
before sending HTTP request, need IP address of
www.google.com: DNS
DNS query created, encapsulated in UDP,
encapsulated in IP, encapsulated in Eth. To
send frame to router, need MAC address of
router interface: ARP
ARP query broadcast, received by router,
which replies with ARP reply giving MAC
address of router interface
client now knows MAC address of first hop
router, so can now send frame containing
DNS query