4-6 Network Layer.pptx

8/13/2019 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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4-6 Network Layer.pptx