Clients and Servers

• Both are computers, depends on their purpose
• Networking’s purpose is to get ‘data’ from one to the other
• …. even when they are on the other side of the world

Take a look at

$ ping brandeis.edu
$ traceroute brandeis.edu

Basic Terms

• Host: On the internet, a computer that is part of the network is often referred to as a host
• MAC address: A totally unique number assigned at time of manufacture to every piece of hardware that can be connected to the network. Media Access Control address. It “cannot” be changed.
• IP Address: Internet Protocol Address, e.g. 12.44.23.123
• Domain name: A name assigned to a host on the internet, e.g. brandeis.edu
• DNS: Domain Name System. An internet-wide service (a distributed database) that associates ip addresses to domain names

MAC addresses, IP addresses and DNS

• User types in a domain name
• Target computer is identified by an IP address
• So: Need a phonebook of some kind
• DNS: distributed name service

Basic Network utility programs

• ping: sends a message to a destination host and listens that the packet is sent back
• traceroute: similar, but records the intervening hosts
• ifconfig: list network interfaces and what IP address they are associated with
• netstat: A really verbose printout of all the local TCP/IP ports and whats going on
• nslookup: Look up the ip address of a domain name
• whois: lookup what the internet knows about the owner of a certain domain name

More about IP

• So the IP address is for 1 specific ‘host’ or server (as usual there are exceptions :)
• IP is the way servers talk ‘to each other’ to get a packet of bits between them
• Conceptually, ‘send these bits to this ip address’
• What’s a port number
• TCP/IP: what it means