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Old 09-09-2007, 03:28 PM
Diego_ Diego_ is offline
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Default few network issues!

Hi guys,

I've got to solve the following network problems, if you know the answers please answer. Thank you!


1) What are the drawbacks of having a too small or too large time-out for the ARP cache entries ?

2) In which cases a hostdoesnot need touse ARP to sendan IP datagram ?

3) Explain why or why not it is a good idea to generate ICMP error messages for the following datagrams:
a) Adatagram thatwas sent toa an exceeded TTL.
b) An ICMP error message.
c) Adatagram withIP broadcastdestination.
d) A datagram fragment,which isnotthe ?rst.
e) Adatagram witha destinationthat isnotin theroutingtable.
f) Adatagram withan invalidchecksum.

4) Calculate the maximum theoretical throughput of TCP on an 10 Mbits/sec Ethernet,assuming a MSS of 1024 bytes. Suppose that neither IP nor TCP carry options, and remember the minimum time between frames(9.6s) and the minimum size for data in Ethernet(46bytes).

Preamble (64) Source (4 Destination(4 Type(16) Data CRC (32)

5) The host A establishes a TCP connection to host B in which the first sequence number will be 45000. If A sends bytes up to the one numbered 46024, and afterward the 45274, which can be the size of thesendingwindow? 46022 46023 46024 45274

Sending sequence:
... 46022 46023 46024 45274 ...

6) (a) A client uses TCP for sending data to a server. Data are 16 bytes. Calculate the performance of the transmissionat TCP level(ration between useful bytesand total). Consider that the are no extra optionsinthe TCP header.

(b) A client uses UDP for sending data to a server. Data are 16 bytes. Calculate the performance of the transmission at IP level (ration between useful bytes and total). Consider that the are no extra optionsinthe IP header.

7) (a) The administrator of an Autonomous System SA wants to hide the network X from neighbour SA1. To do this,she does not include the information about X in the advertisement of her networks. Is this protection effective? And if she wants to hide it only internally to SA1 ?
Explain the connectivity of this network to/from other networks.

(b) Do broadcast messages go through Internal Routers (IR)? And through Border Routers (BR)? Explain the implications of an affirmative answer to this last question.

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