A. Suppose you query a root name server for an A record for www.facebook.com. What is the

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Question:

A. Suppose you query a root name server for an A record for www.facebook.com. What is the most likely reply?

1. An answer section including a single A record for www.facebook.com.

2. An authority section including an NS record for facebook.com and an additional section containing an A record for the named host.

3. An answer section including more than one A record for www.facebook.com

4. An authority section of one or more NS records for .com name servers and no additional section.

5. An answer section of one or more NS records for .com name servers and an additional section of NS records for other root servers.

6. An authority section of one or more NS records for .com name servers and an additional section of A records for those name servers.

B. Your friend has hired a service to serve DNS records for her domain. She almost immediately adds an A record to her domain and finds that she can look it up immediately. She does not share the name with anyone and so no one else ever looks it up. A few weeks later, you two are in a home with a broadband connection and are both connecting to the Internet through its WiFi network. She checks that DNS is still working correctly by looking up the name, then modifies the A record to have a different IP address. She looks up the name again and finds that lookups are still going to the old address. She tries several more times, then tries with your computer. In all cases the query returns the old address. She asks you what is wrong. Which answer is the most likely cause?

1. The DNS provider has updated its database but your friend's DNS resolver still has the old A resource record whose TTL hasn't expired.

2. All of the computers have cached A records for the name whose TTL has not expired.

3. The DNS provider has updated its database but is waiting for the TTL on the existing A record to expire before updating it.

4. The DNS provider, now safe that she's a customer, is being lazy and not quickly updating its database.

C. You issue a recursive query for www.stanford.edu directly to the DNS root servers (you do not use a resolver). Which of the following are likely to be true about the response? Check all that apply.

1. The response will include an A record for www.stanford.edu

2. The response will include an NS record for the .edu domain

3.The response will include an A record for root name servers.

4. The response will have the RA bit set in its header.

5. The response will have the TC bit set in its header.

6. The response will have the RD bit set in its header.

D. Assuming a resolver has no cache, looking up the A record for a name such as www.stanford.edu requires talking to several servers. A more efficient solution would be to have a large unified database for name lookup so you only have to contact one server. Why does DNS use a hierarchy? Check all that apply.

1. Each domain can have its own name servers, distributing management and control.

2. Host names initially mirrored the IP address hierarchy, so having a hierarchy of names would match this structure well.

3. Network file sharing was an early application for the Internet, and a hierarchy of names resembles the hierarchy of folders and files. NS records represent directories and A records represent files.

4. Building one large database that is robust to node failures is more difficult than a distributed solution where node failures only hurt one subset of the namespace.

5. It distributes load across the servers responsible for different subtrees and levels.

6. Because the Internet was intended to have centralized control by ARPA, a hierarchy allowed ARPA to control the root of the name system and therefore the Internet.

7. Jon Postel didn't want any responsibility but everyone else wanted him in charge, so they designed a system that required a central administrator and convinced him to take the job.