Naming
Several types of names exist in the Internet design model.
An understanding of each is critical to the engineer.
Domain Names
are alphanumeric strings used by users to identify
Internet hosts. www.FreeSoft.org is a domain name. Domain
names are converted into IP addresses by
DNS.
IP Addresses
are 32-bit numbers used to identify Internet hosts
by the IP Protocol. Sometimes
IP addresses must be written in a human-readable
format; dotted quad notation is used, with each of the four bytes
written as a decimal number, separated by periods. 205.216.34.7
is a dotted quad IP address.
Service Names are short strings that identify particular
services on an Internet host. They must be converted to port numbers
before use, which is commonly done using a services table,
/etc/services on UN*X machines. Examples of service names
are telnet, smtp, and http.
Port Numbers identify particular services on an Internet host
to the
TCP and
UDP
Protocols. They are 16-bit numbers, usually written in decimal, and
known by convention. For example, port 25 is used for SMTP mail transfers,
and port 80 for HTTP Web transfers.
Universal Resource Locators (URLs)
are used by the World Wide Web to locate and identify Web documents and
other resources. URLs typically contain service names,
domain names and sometimes port
numbers. URLs also include a string, usually a filesystem path, to
distinguish between different documents available through a single server.
