1. TCP/IP Networking An Example
Introductory material.
This module illustrates the interactions of the protocols of the TCP/IP protocol suite with the help of an example. The example intends to motivate the study of the TCP/IP protocols.

2. A simple TCP/IP Example
A user on host “Argon” makes a web access to a URL on host:
What actually happens in the network?

3. HTTP Request and HTTP response
Web browser runs an HTTP client program
HTTP client sends an HTTP request to HTTP server
Web server runs an HTTP server program
HTTP server responds with HTTP response

4. From HTTP Request to Response
At Argon:
HTTP - > find the server: DNS (Neon name to Neon IP address)
HTTP - > TCP (set up a connection to port on server (Neon) to send request)
TCP -> IP (forward request across Internet – after connection setup)
IP -> DataLink (send data hop by hop, across routers, over network links)
DataLink -> IP (accept received data on link)
IP -> TCP (extract user data)
TCP -> HTTP (receive response, process user data)
At Neon:
IP -> TCP (extract user data, check integrity, ACK)
TCP -> HTTP (process user data: create response to send to Argon)
HTTP - > TCP (take response and forward back to client)
TCP -> IP (send data to IP to forward across Internet) 1 2
Sending Data 5
Receiving Data 3 4

5. Data Path across the Network
Http Request
Http Response

6. Snapshot at Argon’s side
tcpdump: listening on fxp0
16:54: > : 1+ A? neon.cs. (25)
16:54: > : 1 NXDomain* 0/1/0 (98) (DF)
16:54: > : 2+ (41)
16:54: > : 2 NXDomain* 0/1/0 (109) (DF)
16:54: > : 3+ (38)
16:54: > : 3* 1/1/2 (122) (DF)
16:54: arp who-has tell
16:54: arp reply is-at 0:e0:f9:23:a8:20
16:54: > : S :607568(0) win 8192
<mss 1460> (DF)
16:54: > : S : (0)
ack win <mss 1460> (DF)
16:54: > : . ack 1 win 8760 (DF)
16:54: > : P 1:60(59)
ack 1 win (DF) [tos 0x10]
16:54: > : . ack 60 win 8701 (DF)
DNS
IP to h/w (DataLink)
TCP Connection setup to port on server
HTTP Request