[VUSR] 64684 CS610 Assignment No 4 Solution Fall 2011

Assignment Statements:
Q1. If the application selects a datagram size greater than
MTU along the path to the destination. How to handle this
situation? Illustrate your answer with your own words.
Sol:

MTU:
Every hardware technology specification includes the definition of the maximum size of
the frame data area, which is called the Maximum Transmission Unit (MTU). Any
datagram encapsulated in a hardware frame must be smaller than the MTU for that
hardware.
FRAGMENTATION:
One technique is to limit datagram size to smallest MTU of any network. IP uses
fragmentation i.e. datagrams can be split into pieces to fit in network with small MTU.
Router detects datagram larger than network MTU and then it splits into pieces and each
piece is smaller than outbound network MTU.
Each fragment is an independent datagram. It includes all header fields. Bit in header
indicates that the datagram is a fragment. Other fields have information for reconstructing
original datagram. Fragment offset gives original location of fragment.
Router has local MTU to computer size of each fragment. It puts part of data from
original datagram in each fragment and puts other information into header.

Read more: CS610 Assignment No 4 Solution & Discussion Due Date: 10-01-2012 - Virtual University of Pakistan http://vustudents.ning.com/group/cs610computernetwork/forum/topics/cs-610-computer-networks-assignment-04#ixzz1j7qat8CR

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Q2: How can ICMP be used for automated tool and Path
discovery? Illustrate your answer with your own words.
Sol:

AN ERROR REPORTING MECHANISM (ICMP)
INTRODUCTION:
IP provides best-effort delivery. Delivery problems can be ignored; datagrams can be
'dropped on the floor'. Internet Control Message Protocol (ICMP) provides error
reporting mechanism.

INTERNET CONTROL MESSAGE PROTOCOL:
Some errors can be reported. Router sends message back to source in datagram. Message
contains information about problem. It is encapsulated in IP datagram.

USING ICMP TO TEST REACHABILITY:
ICMP can also be used to test different tools. An Internet host A, is reachable from
another host B, if datagrams can be delivered from A to B. Ping program tests reachability.
It sends datagram from B to A, that echoes back to B. it uses ICMP echo request
and echo reply messages. Internet layer includes code to reply to incoming ICMP echo
request messages.

USING ICMP FOR PATH MTU:
Fragmentation should be avoided. Source can configure outgoing datagrams to avoid
fragmentation. Source determines path MTU- smallest network MTU on path from
source to destination. Source probes path using IP datagrams with don't fragment flag.
Router responds with ICMP fragmentation required message. Source sends smaller
probes until destination reached.

Read more: CS610 Assignment No 4 Solution & Discussion Due Date: 10-01-2012 - Virtual University of Pakistan http://vustudents.ning.com/group/cs610computernetwork/forum/topics/cs-610-computer-networks-assignment-04#ixzz1j7qj5XH0

 

 

 

 

 

                    

 

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