Consider a situation in which a cyberterrorist makes all the DNS servers in the world crash simultaneously. How does this change one�s ability to use the Internet?

THE APPLICATION LAYER

PROBLEMS

1. Many business computers have three distinct and worldwide unique identifiers. What are they?

2. In Fig. 7-4, there is no period after laserjet. Why not?

3. Consider a situation in which a cyberterrorist makes all the DNS servers in the world crash simultaneously. How does this change ones ability to use the Internet?

4. DNS uses UDP instead of TCP. If a DNS packet is lost, there is no automatic recovery. Does this cause a problem, and if so, how is it solved?

5. John wants to have an original domain name and uses a randomized program to generate a secondary domain name for him. He wants to register this domain name in the com generic domain. The domain name that was generated is 253 characters long. Will the com registrar allow this domain name to be registered?

6. Can a machine with a single DNS name have multiple IP addresses? How could this occur?

7. The number of companies with a Web site has grown explosively in recent years. As a result, thousands of companies are registered in the com domain, causing a heavy load on the top-level server for this domain. Suggest a way to alleviate this problem without changing the naming scheme (i.e., without introducing new top-level domain names). It is permitted that your solution requires changes to the client code.

8. Some email systems support a Content Return: header field. It specifies whether the body of a message is to be returned in the event of nondelivery. Does this field belong to the envelope or to the header?

9. Electronic mail systems need directories so peoples email addresses can be looked up. To build such directories, names should be broken up into standard components (e.g., first name, last name) to make searching possible. Discuss some problems that must be solved for a worldwide standard to be acceptable.

10. A large law firm, which has many employees, provides a single email address for each employee. Each employees email address is @lawfirmdotcom. However, the firm did not explicitly define the format of the login. Thus, some employees use their first names as their login names, some use their last names, some use their initials, etc.