Assignment 4
Introduction
Please answer the questions precisely and concisely. Every question can be answered in one or at most a few sentences. I will not have the patience to read long paragraphs or essays and you may lose credit for possibly correct answers.
Submit your work via sakai as a plain text or pdf document. No Microsoft Word, Apple Pages, ePub, et cetera formats.
Reading
Text: pages 98–144 (section 2.2 - 2.5.3)
Questions
1.
[Kurose & Ross text: page: 170, question R15]
Why is it said that FTP sends control information “out-of-band”?
2.
[Kurose & Ross text: page: 170, question R18]
From a user’s perspective, what is the difference between the download-and-delete mode and the download-and-keep mode in POP3?
3. Read HTTP cookies explained. What happens if a cookie is not given an expiration time?
4. ARIN, the American Registry for Internet Numbers, manages IP address assignments to organizations (ISPs and other companies that have been assigned IP addresses directly by them). You can query these allocations via the SEARCH Whois box at the top right of www.arin.net. You can enter an organization name, such as Google, Comcast, or Rutgers (note: it’s the organization name, not the domain name). You can also enter an IP address to do a reverse DNS search. Alternatively, you can use the whois command on Linux or OS X systems to query domain or address ownership. See the wikipedia entry to learn more about whois.
4a. What company owns the address 66.135.216.190?
4b. What company owns the address 9.8.7.6?
5. The dig command on Linux and OS X systems is a program that queries DNS servers. It performs lookups and displays answers. You can see the documentation [here][] or run the command man dig. For example,
dig +nocmd rutgers.edu NS +noall +answer
sends a name server (NS) query and will show you all the authoritative DNS servers registered for rutgers.edu. The ++nocmd option tells the command not to print the initial comment identifying the version of dig and its options. The +noall option omits showing the DNS query options, the query command that was sent, and the answer unless you explicity ask for a section (try running the command with and without +noall). The +answer option says you want to display the answer section of the DNS query. The answer section is the response data to the query (called the question).
As another example,
dig +nocmd google.com ANY +multiline +noall +answer
performs an ANY request, which asks the DNS resolver for all information it has about the domain. This may include mail servers (MX records), IP addresses for the host name (A records), aliases (CNAME records), and other fields. The +multiline option prits certain records, such as the SOA record (start of authority, which defines key information about the zone) in a more verbose multi-line format with comments.
5a. What are the DNS servers that are responsible for the amazon.com domain? Don’t list the entire output of the dig command; just list the names of the name servers.
5b. What is the mail server (MX record) for cs.rutgers.edu?
5c. gmail.com defines five redundant mail servers. What are they?
