CS417 Exam 3

Fall 2013

Paul Krzyzanowski

    Part I – 22 points

  1. 6 points
    How does a clustered file system differ from a distributed file system (e.g., NFS, SMB, AFS, Coda)?
  2. 6 points
    Why is it important to use consistent hashing in a distributed hash table? Note: The question is not asking you to define consistent hashing.
  3. 6 points
    Explain the difference between a public key and symmetric algorithm.
  4. 6 points
    Alice sends Bob her X.509 digital certificate. Bob validates the certificate successfully. How does he now validate that he is indeed communicating with Alice?
  5. Part II – 78 points – 3 points each

    For each statement, select the most appropriate answer. I will give you credit for two incorrect answers.

  6. A digital signature or message authentication code can protect us from certain:
    (a) Byzantine faults.
    (b) Fail stop faults.
    (c) Fail silent fault.
    (d) Fail restart faults.
  7. Chubby's fault tolerance model is:
    (a) Active-active.
    (b) Active-passive.
    (c) Triple modular redundancy (TMR).
    (d) Five-way modular redundancy (5-MR).
  8. For a system to be k-fault tolerant in the presence of faults that may be either byzantine or fail-silent, you need this many components:
    (a) k + 1
    (b) 2(k+1)
    (c) 2k + 1
    (d) k2 + 1
  9. An asynchronous network makes it difficult to design a system that will:
    (a) Determine that a computer is not communicating.
    (b) Determine the ordering of events.
    (c) Identify the origin of a message.
    (d) Distinguish causal messages from concurrent messages.
  10. Quorum in a cluster is important to ensure that:
    (a) More than one group of computers do not create their own cluster.
    (b) There is sufficient computing power available for the task.
    (c) All computers in the cluster are alive.
    (d) All computers in the cluster have a backup.
  11. A heartbeat is used to:
    (a) Detect dead computers in a cluster.
    (b) Synchronize operations in a cluster.
    (c) Provide high-speed communication links within a cluster.
    (d) Propagate configuration changes throughout the cluster.
  12. A load balancer is least useful for:
    (a) Migrating processes from one computer to another.
    (b) Distributing requests among a pool of servers.
    (c) Fault tolerance.
    (d) Allowing an administrator to take a server out of a cluster for upgrades with no downtime.
  13. Map workers and Reduce workers in a Google MapReduce cluster use this failover model:
    (a) Cold
    (b) Warm
    (c) Hot
    (d) Passive
  14. A Google cluster comprises computers that are selected for the:
    (a) Best energy efficiency to performance ratio.
    (b) Maximum CPU performance.
    (c) Fastest local storage.
    (d) Smallest size.
  15. Looking up the address and port of a server at the start of a client process is an example of:
    (a) Static binding.
    (b) Early binding.
    (c) Late binding.
    (d) Delayed binding.
  16. The Domain Name System (DNS) is built with a distributed lookup that uses:
    (a) A central coordinator.
    (b) Flooding.
    (c) Referrals.
    (d) A distributed hash table.
  17. An overlay network is a:
    (a) Set of connections that define a spanning tree to ensure there are no cycles.
    (b) Private network of high-speed connections that overlays part of the public Internet.
    (c) Wireless network that overlays the wired Internet.
    (d) Graph whose edges identify nodes that know about each other.
  18. CAN, the Content-Addressable Network is a peer-to-peer storage system that:
    (a) Allows a client to locate an object by any of its content instead of a key.
    (b) Enables a client to locate an object via multiple keys, one per axis in each dimension.
    (c) Transforms a key into an address of the server holding the corresponding object.
    (d) Hashes a single key into multiple axes, one per dimension.
  19. A finger table in a Chord node is:
    (a) A table of frequently used key?node mappings.
    (b) A tree structure that enables a node to find any other node in O(log N) table reads.
    (c) A table with each element, i, representing a node that is i hops away.
    (d) A table with each element, i, representing a node that is 2i hops away.
  20. Dynamo's structure is most similar to:
    (a) Bigtable.
    (b) Flooding.
    (c) Chord.
    (d) CAN.
  21. Unlike Bigtable, with Amazon Dynamo:
    (a) Keys are sorted alphabetically to support iteration.
    (b) An object is identified by exactly one key.
    (c) Two processes may write conflicting updates.
    (d) All requests pass through a coordinator.
  22. Virtual nodes in Amazon Dynamo are designed to:
    (a) Improve fault tolerance due to the replication of nodes.
    (b) Increase the requests the system can handle since many virtual nodes can be managed by one physical node.
    (c) Improve load distribution when adding or removing nodes.
    (d) Create an overlay network that arranges nodes into a logical ring.
  23. Akamai uses DNS to resolve a domain name to:
    (a) The nearest server that has the desired cached content.
    (b) A load balancer that then forwards the request to any available caching server.
    (c) A coordinator that will analyze the request and forward it to the nearest caching server.
    (d) The original server, which then sends an HTTP REDIRECT message to the nearest caching server.
  24. A hash function is useful in the generation of a:
    (a) Nonce.
    (b) Symmetric key.
    (c) Digital signature.
    (d) Session key.
  25. SSL is an example of a:
    (a) Symmetric key cryptosystem.
    (b) Public key cryptosystem.
    (c) Hybrid cryptosystem.
    (d) Restricted cipher.
  26. The Challenge Handshake Authentication Protocol (CHAP) tests to see if you know a:
    (a) Secret value.
    (b) Public key.
    (c) Private key.
    (d) Session key.
  27. Alice wants to talk to Bob and gets a ticket from a Kerberos server. The ticket is:
    (a) Encrypted so only Alice can decode it.
    (b) Encrypted so only Bob can decode it.
    (c) Encrypted so only Alice and Bob can decode it.
    (d) Not encrypted but contains a digital signature so that Alice and Bob can validate it.
  28. A random number generator is NOT useful for generating a:
    (a) Nonce.
    (b) Symmetric key.
    (c) Digital signature.
    (d) Session key.
  29. With OpenID, a web site:
    (a) Identifies the user but allows another site to authenticate the user.
    (b) Sends the user's ID and password to another site to validate them.
    (c) Requests the user's password from the Identity Provider and uses that to authenticate the user.
    (d) Provides anonymous login capabilities since the site never knows the identity of the authorized user.
  30. OAuth differs from OpenID in that it:
    (a) Handles authentication while OpenID is responsible for identification.
    (b) Sends the user to another site to approve access to specific services at that site.
    (c) Uses the HTTP REDIRECT to send the user to a third-party site.
    (d) Provides a centralized server to manage information access requests for all users.
Last modified March 24, 2020.
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