Each interface in an IP network has a 32-bit address. Because 32 is a large number, IP addresses are written in dotted-decimal notation. Each byte is converted to decimal and separated from the next byte by a dot, for example, 192.168.0.1. An IP address contains a network and host field. Each interface is configured with a network and host number, and an indication of the network field length. The length can be specified as a subnet mask (255.255.255.0) or in CIDR notation, such as /24.

 

The Domain Name System (DNS) is an application-layer, client/server protocol that allows Internet users to reach servers by name, rather than by a numeric IP address. DNS is a protocol as well as a system of servers that provide naming. The servers implement a distributed, hierarchical database of Resource Records (RRs) that map names to addresses, addresses to names, and other information.

 

This is the 2nd podcast dealing with Internet email. In this podcast we introduce techniques for recognizing a phishing scam. Phishing is a popular Internet scam where the perpetrators send email falsely claiming to be a legitimate enterprise in an attempt to get the recipient to surrender private information such as a credit card number or bank account number. We also use this practical example to further our teaching of Internet protocols, and introduce IP addresses and DNS names.

 

In this episode we discuss the protocols used for sending and retrieving email. This is the first of two episodes on email. The next episode will talk about phishing, a type of scam that uses email. In this episode we cover email protocols. Simple Mail Transfer Protocol (SMTP) is used for sending email and Post Office Protocol (POP) and Internet Message Access Protocol (IMAP) are used for downloading email.