COMS 3157 Advanced Programming

12 - Introduction to TCP/IP networking

Pipes

simplest form of one-way interprocess communication

• created by pipe() system call (see man 2 pipe)

• usually called by a process before it forks in order to setup a communication channel between child processes

• example:

  echo | ~jae/cs3157-pub/lab4/mdb-lookup-cs3157 | grep '{}'
  

TCP/IP networking

Sockets are similar to pipes, but:

• two way
• connects remote processes

5 protocol layers of TCP/IP

• protocols of the Internet
• sockets API sits between layer 4 & 5
• we’ll take layer 1 - 4 as blackbox (learn them in W4119)

IP address

• 32-bit integer
• usually written in dotted-quad notation: 128.59.0.5
• DNS translates hostnames, such as tokyo.clic.cs.columbia.edu, into an IP address

Port numbers

• need to distinguish between many network apps in a host
• unsigned 2-byte int: 1 - 65535 (0 is reserved)
• fixed # for well-known apps (ex. 80 for web servers)

Client-server model

• server “listens” on a known port
• client “connects” to it
• from that point on, 2-way communication

netcat: TCP/IP swiss army knife

• see man nc

• connects stdin/stdout with a socket

• server mode: nc -l <port>

client mode: nc <hostname or IP addr> <port>

• can we turn our mdb-lookup-cs3157 into a network server using nc and some pipes?

  • yes, but we’ll need a “named pipe” (see man mkfifo)