Suppose a device is connecting to the UWaterloo campus network and requests www.google.com.

Device must first connect to the internet.

• Connecting laptop needs its own IP address + adress of first-hop router + address of DNS server
  • Information is obtained via DHCP
• DHCP request is encapsulated in UDP → encapsulated in IP → encapsulated in 802.3 Ethernet
• Ethernet frame is broadcasted (i.e. dest: FFFFFFFFFFF) on LAN and received at the router running the DHCP server
• Frame is demuxed back to DHCP
• DHCP server formulates DHCP ACK containing:
  • client IP address
  • IP address of first-hop router for client
  • name, IP address of DNS server
• DHCP server encapsulates data in frame and is forwarded (switch learning) through LAN
• Response is demux’d at client
  • Client now has IP address, name + address of DNS server, IP address of its first-hop router

Next, we need ARP to get MAC address of first-hop router for DNS.

• DNS query is created, encapsulated in UDP → encapsulated in IP → encapsulated in Ethernet
• As the MAC address of first-hop router is not known, ARP query is broadcast
• Broadcast is received by router ⇒ ARP reply gives MAC address of router interface
• Client now has MAC address of first-hop router ⇒ can send frame with DNS