President Obama was born in which U'S' state

1
President Obama was born in which U.S. state

• Illinois
• Texas
• New York
• Hawaii
• Trick Question Washington DC
• Kenya

2
Hawaii (4) is right

• He was Senator for Illinois
• George W Bush was Texas
• His father was from Kenya, but had he been born
  there he would probably not have been eligible
  (article 2.1.5 of U.S. constitution)
• DC is indeed not a state, but counts as U.S. for
  the purpose

3
That was the warmup

• Now to check clickers against groups
• IF your group name is shown, please press the
  associated number on each individual clicker AND
  the group clicker
• ELSE wait for next slide(s)

4
Please select a TeamIf youre not here, wait.

• Team A
• Team B
• Team C
• Team D
• Team E

5
Please select a Team If youre not here, wait.

• Team F
• Team G
• Team H
• Team I
• Team J

6
Please select a Team If youre not here, you
should have been done already

• Team K
• Team L
• Team M
• Team N

7
Now for your questions

• Im going to show the individual slide please
  answer as individuals.
• Then Ill ask you to start conferring. Part way
  through this, Ill show the individual answers.
• Then Ill put up the group slide, and ask groups
  to vote using the group clickers only
• A group should vote on its own question

8
I Which of the following scenarios would benefit
most from disabling TCP slow start?

• Many TCP connections between two nodes on the
  same physical LAN with one node connected via a
  physical link consisting of a wireless ethernet
  card.
• Many TCP connections between two nodes connected
  over a WAN. Again one node is connected via a
  physical link consisting of a wireless ethernet
  card.
• Many TCP connections between two nodes on the
  same physical LAN
• Using VOIP over a LAN.
• When transferring a large file over the internet.

9
G Which of the following scenarios would benefit
most from disabling TCP slow start?

• Many TCP connections between two nodes on the
  same physical LAN with one node connected via a
  physical link consisting of a wireless ethernet
  card.
• Many TCP connections between two nodes connected
  over a WAN. Again one node is connected via a
  physical link consisting of a wireless ethernet
  card.
• Many TCP connections between two nodes on the
  same physical LAN
• Using VOIP over a LAN.
• When transferring a large file over the internet.

10
Justification of answers

• We think answer 1 is the scenario that would
  benefit most from having TCP slow start
  disabled. Therefore answer 1 is the "correct"
  answer.
• For 1,2,3 - The fact that 'many' TCP
  connections are made makes little difference. Any
  overhead (CPU/memory) required for many slow
  start algorithms running simultaneously is
  negligible.
• Slow start is about protecting networks

11
I With regard to Silly Window Syndrome (SWS),
Nagles Algorithm

• Solves the problem of SWS.
• Only solves certain cases of SWS.
• Solves SWS when a receiving TCP is serving an
  application that consumes data too slowly.
• Is appropriate when Clarks solution or Delayed
  Ack wont work

12
G With regard to Silly Window Syndrome (SWS),
Nagles Algorithm

• Solves the problem of SWS.
• Only solves certain cases of SWS.
• Solves SWS when a receiving TCP is serving an
  application that consumes data too slowly.
• Is appropriate when Clarks solution or Delayed A
  wont work.

13
Answers

• The answer 2!
• False It only solves half the problem it solves
  it on the sender side, by preventing the sender
  from sending tinygrams, but it doesnt stop the
  receiver from advertising tiny windows.
• True It doesnt solve the problem of the
  application on the receiving side reading data
  too slowly.
• False Clarks solution and delayed
  acknowledgements deal with this side of the
  problem.
• True, but a worse answer than 2 Clarks solution
  and Delayed Acknowledgements are actually solving
  the other half of the problem, and both
  techniques are required to prevent SWS from
  occuring.

14
I Which of these is the most important factor in
the reliability of a secondary DNS server?

• Being located in a different country to the
  primary
• The primary server is polled for changes
  frequently
• Running on the same hardware as the primary
  machine
• Being connected to the net via different routes
  to the primary and other secondary servers

15
G Which of these is the most important factor in
the reliability of a secondary DNS server?

• Being located in a different country to the
  primary
• The primary server is polled for changes
  frequently
• Running on the same hardware as the primary
  machine
• Being connected to the net via different routes
  to the primary and other secondary servers

16
Answer

• Correct RFC 2182 describes best current
  practice as having at least one secondary server
  on a different international backbone to the
  primary server.
• Correct Polling frequently (normally around
  every 3 hours) ensures data is accurate and up to
  date.
• Wrong
• Correct This is (arguably) the best answer, and
  can be implied by 1, but may not be. Two
  countries can use the same pipe to the rest of
  the world, having a primary in one and a
  secondary in the other wouldnt be ideal.

17
Protocol-Independent MulticastHow to do
multicast routing

• PIM is actually a variety of protocols,
• PIM Sparse Mode (PIM-SM) explicitly builds
  unidirectional shared trees rooted at a
  rendezvous point (RP) per group, and optionally
  creates shortest-path trees per source. PIM-SM
  generally scales fairly well for wide-area usage.
  See the PIM Internet Standard RFC 4601
• PIM Dense Mode (PIM-DM) uses dense multicast
  routing. It implicitly builds shortest-path trees
  by flooding multicast traffic domain wide, and
  then pruning back branches of the tree where no
  receivers are present. PIM-DM generally has poor
  scaling properties.1
• Bidirectional PIM explicitly builds shared
  bi-directional trees. It never builds a shortest
  path tree, so may have longer end-to-end delays
  than PIM-SM, but scales well because it needs no
  source-specific state. See Bidirectional PIM
  Internet Standard RFC 5015
• PIM source-specific multicast (PIM-SSM) builds
  trees that are rooted in just one source,
  offering a more secure and scalable model for a
  limited amount of applications (mostly
  broadcasting of content).

18
I In what way is Internet Group Management
Protocol inefficient?

• IGMP has no guarantee that a report is delivered
• IGMP is not a transport protocol, but instead
  instantiates PIM connections
• Multicast use in WANs causes lots of problems
• It is in fact efficient

19
G In what way is Internet Group Management
Protocol inefficient?

• IGMP has no guarantee that a report is delivered
• IGMP is not a transport protocol, but instead
  instantiates PIM connections
• Multicast use in WANs causes lots of problems
• It is in fact efficient

20
Answer Slide

• All answers are true to an extent, but (3) is
  best.
• 1) Although can be a problem, is generally
  solved due to answer 4).
• 2) It creates a group before it implements
  Protocol Independent Multicast. It would be more
  efficient to use this all the time.
• 3) Not fully solved so problems may arise when
  used.
• 4) Has efficiency methods For 1) IGMP sends
  membership query messages repeatedly until an
  acknowledgment is received. Also has scheduling
  so not to send the same report twice.

21
DNS server records (SRV)

• MX records are specific to SMTP, and assume you
  know to use TCP port 25
• You (or your browser) have to guess to stick www
  on the front of a web address, and use TCP port
  80
• Instead, why not look up a generic service
  record, e.g. _smtp._tcp.bath.ac.uk

22
I MX Records serve a similar purpose for SMTP as
SRV Records serve for other protocols.Which of
the following statements do you most agree with?

• It is necessary to have both MX and SRV Records
• MX Records should be phased out and replaced by
  the more generic SRV Records
• MX Records should remain because it would be too
  difficult to replace as their use in email is so
  entrenched them
• SMTP itself is a flawed protocol and should be
  replaced altogether

23
G MX Records serve a similar purpose for SMTP as
SRV Records serve for other protocols.Which of
the following statements do you most agree with?

• It is necessary to have both MX and SRV Records
• MX Records should be phased out and replaced by
  the more generic SRV Records
• MX Records should remain because it would be too
  difficult to replace them their use in email is
  so entrenched
• SMTP itself is a flawed protocol and should be
  replaced altogether

24
Answers

• 1. False. The data stored in SRV Records is a
  superset of the data in MX Records, thus it is
  possible for SRV Records to serve the same
  purpose. 2. Arguably True. For the same reasons
  as 3, its debatable whether the impact on old
  software would cause a major problem. Otherwise,
  as mentioned, SMTP would be trivial to
  change.3. Arguably True. It would be trivial to
  change the SMTP protocol to use SRV Records, but
  old software would still be looking for MX
  Records.
• 4. Debatable. This answer is meant to be thought
  provoking. Why is SMTP one of the few protocols
  that requires its own record?
• SRV has Priority, Weight, Port and Target. MX
  has Priority and Target

25
Networking

• A few questions on the course
• A few questions about the course, and this
  teaching methodology

26
I Good fun, something different and its very
good to be interactive since we do not get much
class participation, except if we want to ask
questions

• Strongly Agree
• Agree
• Neutral
• Disagree
• Strongly Disagree

27
I Although good for general feed-back how we are
doing, its not so good for passing course
material on.

• Strongly Agree
• Agree
• Neutral
• Disagree
• Strongly Disagree

28
I Compared with individually answering, group
answering is

• Much more educational
• Somewhat more educational
• Neutral
• Rather less educational
• Much less educational

29
I My involvement in designing a question has
improved my understanding of networking

• Strongly Agree
• Agree
• Neutral
• Disagree
• Strongly Disagree

30
I Working in groups to design these questions was

• Very beneficial
• Beneficial
• Neutral
• A sad necessity
• Disastrous

31
I Working in groups to answer other groups
questions was

• Very beneficial
• Beneficial
• Neutral
• A sad necessity
• Disastrous