### 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