Homework 6 - Chapter 7

1. DNS queries are done via UDP. How does a DNS client handle lost UDP packets (either the query or the reply), since UDP does no retransmission?
2. Due to the requirements of the IP layer, UDP packets may be as small as 576 bytes. What happens to the DNS lookup if the name to look up is longer than 576 bytes?
3. Can multiple IP addresses have the same domain name? If yes, explain the motivation behind allowing this. If no, explain why not.
4. Can one IP address be associated with multiple domain names? Explain why or why not?
5. Email addresses are typically of the form username@machine.domain. How is DNS used to find the appropriate mail server for an email address?
6. The vacation daemon replies to all emails with a standard message. Is there a situation where two vacation daemons can get stuck in a loop replying to each other's messages? If yes, describe the situation. If no, explain why not.
7. A common feature of an ISP's spam software is to add a header to emails detected as spam. In order to comply with RFC 822, what naming structure does the software need to use for this header?
8. What is the purpose of MIME types?
9. Why are web pages prefixed with MIME headers when served to the client?
10. One common feature of popular PHP forum software is the "Keep me logged in" feature where the website sends an authentication cookie after the user types an appropriate username and password. On future visits, if the cookie is present, the user does not have to provide a password. What are the security implications of such a feature?