A day in life network

People use the network everywhere. 

Today, I learned about the scenario in real world network.

 

This picture shows us how network make us use the internet in daily life.

 

 

 

• Connecting laptop needs to get its own IP address, address of first-hop router, address of DNS server.
  • DNS server: use DHCP
  • DHCP request encapsulated in UDP, encapsulated in IP, encapsulated in 802.3 Ethernet
  • Ethernet frame broadcast(destination: FFFFFFFFFFFF) on LAN received at router running DHCP server
  • Ethernet demuxed to IP demuxed, UDP demuxed to DHCP
   

 

 

• DHCP server formulates DHCP ACK 
  • DHCP ACK containing client's IP address, IP address of first-hop router for client
  • Name & IP address of DNS server
  • Encapsulation at DHCP server, frame forwarded (switch learning) through LAN, demultiplexing at client
  • DHCP client receives DHCP ACK reply
  •  --> Client now has IP address, knows name & address of DNS server, IP address of its first-hop router.
   

 

 

 

• Before sending HTTP request, need IP address of www.~: DNS
• DNS query created, encapsulated in UDP, encapsulated in IP, encapsulated in Eth
• To send frame to router, need MAC address of router interface: APR
• APR query broadcast, received by router, which replies with APR reply giving MAC address of router interface
• Client now knows MAC address of first hop router, so can now send frame containing DNS query

 

 

 

• IP datagram containing DNS query forwarded via LAN switch from client to first hop router
• IP datagram forwarded from campus network into Comcast network, routed (tables created by RIP, OSPF, IS-IS and/or BGP routing protocols) to DNS server.
• Demuxed to DNS server
• DNS server replies to client with IP address of www.~.com.

 

 

 

 

• To send HTTP request client first opens TCP socket to web server
• TCP SYN segment (step 1 in 3-way handshake) inter-domain routed to web server
• Web server responds with TCP SYNACK (step 2 in 3-way handshake)
• TCP connection established!

 

 

 

 

• HTTP request sent into TCP socket
• IP datagram containing HTTP request routed to www.~.com
• Web server responds with HTTP reply (containing web page)
• IP datagram containing HTTP reply routed back to client