Networking A few questions on the course A few questions about the course

The Head of Department is A.Peter Johnson B.Chris Jennison C.Glynis Breakwell D.Phil Willis E.Kevin Edge

That was the warmup I hope you got Phil Willis: Peter Johnson is so last last year! Chris is Phils boss, Kevin is Chriss boss, and Glynis is Kevins boss.

Questions on the course (mostly factual, but there is more to the course than facts)

An Ethernet address is how long? A.Variable length B.16 bytes C.6 bytes D.4 bytes

The answer is C (6 bytes) If you didnt get that, youre pretty confused: After last time, all I can suggest is that you really re-read sections 2.2 and 3.2 of the book.

Which of these is not a well-known routing protocol? A.Routing Information Protocol B.Open Shortest Path First C.Router Discovery Protocol D.Border Gateway Protocol

C Router Discovery Protocol A.RIP is a well-known protocol B.OSPF is a well-known protocol C.RDP, as far as I know, doesnt exist: Router Discovery Messages (chapter 9) say who routers are. D.BGP is a well-known protocol

There are thee kinds of autonomous system: which of these is not one: A.Stub B.Confederation C.Transit D.Multihomed

B (Confederation) is not a kind of autonomous system If you got this wrong, I suggest section 10.7 of the book, and also the updating notes for that

Which one of these statements about IP fragmentation is true A.A fragmented packet can never be refragmented B.Fragments are put together as soon as possible C.Fragmentation is optional for the sender D.Fragmentation is what happened to officers in Vietnam E.It is vital that fragments arrive in the right order

C (optional) is the right answer A.fragmented packets can be re- fragmented B.The receiver (or its firewall) puts fragments together, not intermediate hosts C.True: set the DF flag D.Thats not IP fragmentation E.Fragments can arrive in any order: the offset field tells how to put them back

Which one of these is true A is called limited broad- cast because its only used on startup B.Broadcasting is how internet radio works C.Given the choice, multicast is generally better than broadcast D.Multicasting only works on Ethernets

The answer was C: multicast is generally better than broadcast A.Its called limited because routers dont forward it, so its limited to that net B.Internet radio etc. work on multicasting C.Yes – doesnt load those who arent interested D.No: multicasting is very important on wide-area networks (e.g. radio)

Between A and PTR records A.The DNS is always consistent B.Consistent except for deliberate fraud C.Might well be inconsistent D.Consistency is meaningless E.Consistency is undecidable

A thinking question: C or E A.Certainly not true B.Fraud can certainly work by adding inconsistencies, but its not the only way C.DNS maintainers can easily screw up! D.An abstract definition is possible E.But it requires testing infinitely many possible cases. Also the DNS is distributed, so untestable.

The DNS … A.Always uses UDP B.Always uses TCP C.Normally uses UDP D.Questions are in UDP, but replies can be in either depending on length.

C normally UDP Both can be used UDP is more common for most transactions Hence C is the answer A UDP question always gets a UDP answer, possibly marked TC (truncated). It can be re-asked in TCP if necessary

Which one of these statements about TFTP is true A.TFTP was invented before TCP, so uses UDP B.TFTP, like UDP, is unreliable C.TFTP is obsolete D.TFTP uses UDP for simplicity

D simplicity A.No – TCP is RFC 793 but TFTP is RFC Anyway date isnt the reason B.TFTP numbers packets, and asks for repeats, so is reliable C.TFTP is in daily use in the Library D.Simplicity is the reason: UDP is simple, unchanging and fits in a boot PROM.

The TCP header is A.Exactly 20 bytes long B.At least 20 bytes long C.At most 20 bytes long D.Exactly 60 bytes long E.Between 20 and 60 bytes long

E (between 20 and 60) A.20 is the minimum B.Correct, but not the whole truth C.Wrong D.60 is the maximum, but its nearly always less E.Correct

The ACK bit in the TCP header is set A.All the time B.Only when theres new data being acknowledged C.On every packet except the first D.On every packet except the first in each direction

C every packet except first A.Cant be set on first packet theres nothing to acknowledge B.The data might not seem new to us, but our previous acknowledgement might have been lost C.Correct D.No the first packet from B to A has to acknowledge As SYN

A TCP segment with SYN must have a byte of data, so that it can be acknowledged 1.True 2.False

False The SYN bit itself is counted as if it were a byte of data. It is this pretend byte that is acknowledged.

The initiator of a TCP connection must be the one to close it. 1.True 2.False

False In a typical client-server situation, it is often the client (which is the one who starts the connection) who finishes it, but this is not an invariable rule. HTTP is a counter- example (at least in HTTP 0.9/1.0)

Networking A few questions on the course A few questions about the course (starting with some comments from the survey some of you kindly did)

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 1.Strongly Agree 2.Agree 3.Neutral 4.Disagree 5.Strongly Disagree

Although good for general feedback how we are doing, its not so good for passing course material on. 1.Strongly Agree 2.Agree 3.Neutral 4.Disagree 5.Strongly Disagree

I wish wed had more networking earlier in the degree course 1.Strongly Agree 2.Agree 3.Neutral 4.Disagree 5.Strongly Disagree

I wish this Audience Response System had been used earlier (i.e. in previous years) 1.Strongly Agree 2.Agree 3.Neutral 4.Disagree 5.Strongly Disagree