4-6 network layer.pptx
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Network Layer (Part 6)
Computer Networks
Tutun JuhanaTelecommunication EngineeringSchool of Electrical Engineering & Informatics
Institut Teknologi Bandung
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INTERNET CONTROL MESSAGEPROTOCOL VERSION 4 (ICMPV4)
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The value of the protocol field in the IP datagram is 1 to indicate
that the IP data is an ICMP message
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Messages
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includes the IP
header of
the originaldatagram + the first
8 bytes of data in
that datagram
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Provides port numbers
(UDP and TCP) and
sequence number
(TCP).
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ERROR REPORTINGMESSAGES
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Error Reporting Messages
No ICMP error message will be generated in response to a
datagram carrying an ICMP error message.
No ICMP error message will be generated for a fragmented
datagram that is not the first fragment.
No ICMP error message will be generated for a datagram having a
multicast address.
No ICMP error message will be generated for a datagram having a
special address such as 127.0.0.0 or 0.0.0.07
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Destination Unreachable
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Note: For codes, please refer to Forouzans
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Source Quench
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Time Exceeded
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Parameter ProblemIf a router or the destination host discovers an ambiguous
or missing value in any field of the datagram, it discards thedatagram and sends a parameter-problem message back
to the source
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Redirection
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QUERY MESSAGES
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Query Messages
ICMP can also diagnose some network
problemsaccomplished through the
query messages
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Echo Request and Reply
The echo-request and echo-reply messages aredesigned for diagnostic purposes
Network managers and users utilize this pair of
messages to identify network problems.
The combination of echo-request and echo-reply
messages determines whether two systems
(hosts or routers) can communicate with each
other.
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Timestamp Request and Reply
Two machines (hosts or routers) can
use the timestamp-request and
timestamp-reply messages to: determine the round-trip time needed for
an IP datagram to travel between them
synchronize the clocks in two machines
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CHECKSUM
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In ICMP the checksum is calculated over
the entire message (header and data)
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DEBUGGING TOOLS
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Ping
We can use the ping program to find if a host is alive andresponding
The source host sends ICMP echo request messages
(type: 8, code: 0); the destination, if alive, responds with
ICMP echo reply messages
The ping program sets the identifier field in the echo
request and reply message and starts the sequence
number from 0; this number is incremented by one each
time a new message is sent
Note that ping can calculate the round-trip time. It inserts
the sending time in the data section of the message.
When the packet arrives it subtracts the arrival time from
the departure time to get the round-trip time (RTT).
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Traceroute
The traceroute program in UNIX or tracert
in Windows can be used to trace the route
of a packet from the source to the
destination
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