CCNA2 M8 TCIPIP Error Control Messages

8/14/2019 CCNA2 M8 TCIPIP Error Control Messages

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CCNA Semester2

Module 8

TCP/IP and Error Control Messages

Objectives

TCP/IP error messages TCP/IP control messages


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Overview of TCP/IP Error

Message

IP Limitation

IP is an unreliable, best effort deliverymechanism.

No built-in processes to ensure that data isdelivered in the event that problems exist withnetwork communication.

If an intermediary device such as a router fails,or if a destination device is disconnected fromthe network, data cannot be delivered.


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Internet Control Message Protocol

ICMP is the componentof the TCP/IP protocolstack that addresses

the basic limitation ofIP.

ICMP does notovercome theunreliability issues inIP. Reliability must beprovided by upperlayer protocols if it isneeded.

Error reporting and error correction

ICMP is an error reporting protocol for IP. When datagram

delivery errors occur, ICMP is used to report these errors back

to the source of the datagram.


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ICMP message delivery

ICMP messages are encapsulated into datagrams in thesame way any other data is delivered using IP.

ICMP messages are transmitted in the same way as any

other data, they are subject to the same delivery failures.For this reason, errors created by ICMP messages donot generate their own ICMP messages.

Network Communication

Network communication requires basic

conditions:

sending and receiving devices must have the TCP/IP

protocol stack properly configured.

default gateway must also be configured if datagrams are

to travel outside of the local network intermediary devices must be in place to route the

datagram from the source device and its network to the

destination network.


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Unreachable Networks

Using ping to test destination reachability


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Detecting excessively long routes

ICMP uses a time exceeded message to notify thesource device that the TTL of the datagram hasbeen exceeded.

Echo messages

All ICMP message formats start with these same three

fields:

Type: the type of ICMP message being sent.

Code: includes further information specific to the message type.

Checksum: verify the integrity of the data.


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ICMP Message Type

Destination unreachable message

Datagrams cannot always be forwarded to their

destinations. In these cases, ICMP delivers back to the

sender a destination unreachable message indicating to

the sender that the datagram could not be properly

forwarded.


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Destination unreachable message

Miscellaneous error reporting

Devices that process datagrams may not be able to

forward a datagram due to some type of error in the

header. In this case, an ICMP type 12 parameter problem

message is sent to the source of the datagram.


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TCP/IP Suite Control Messages

Introduction to control messages

Unlike error messages, control messages are

not the results oflost packets or error

conditions which occur during packet

transmission.

Instead, they are used to inform hosts of

conditions such as network congestion or theexistence of a better gateway to a remote

network.


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ICMP Redirection

R1 forwards the packet

and sends an ICMP

redirect / change request

to Host H telling it to use

R2 as the gateway to

forward all future

requests to network

10.0.0.0/8.

Redirect/Change Request Message


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ICMP Timestamp Request

The ICMP timestamp request message allows a host toask for the current time according to the remote host.The remote host uses an ICMP timestamp reply

message to respond to the request.

Transit Time Estimation

Using the timestamps, the host can estimatetransit time across the networks.

The host that originated the timestamp requestcan also estimate the local time on the remotecomputer.

More robust protocols such as Network TimeProtocol (NTP) at the upper layers of the TCP/IPprotocol stack perform clock synchronization ina more reliable manner.


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Information requests and reply message

Allow a host to determine its network number.

Other protocols such as BOOTP and DHCP are

now used to allow hosts to obtain their networknumbers.

Address mask requirements

If a host does not know the subnet mask, it may

send an address mask request to the local

router.

When the router receives the request, it will

respond with an address mask reply. This

address mask reply will identify the correctsubnet mask.


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Router discovery message

The host, has not been manually configured

with a default gateway, can learn of available

routers through the process of router discovery. This process begins with the host sending a

router solicitation message to all routers, using

the multicast address 224.0.0.2 as the

destination address.

Router discovery message

When a router that supports the discovery process

receives the router discovery message, a router

advertisement is sent in return.


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Router solicitation message

A host generates an ICMP router solicitation message in

response to a missing default gateway.

A local router will respond with a router advertisementidentifying the default gateway for the local host.

Congestion and flow control messages

Packets dropped occur as there is too much congestion

ICMP source-quench ask senders to reduce the transmission

rate

Sender slowly increase the transmission rate as no other

source-quench messages are received.


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Summary

ICMP error and control messages

ICMP destination unreachable

ICMP echo message

ICMP redirect

ICMP timestamp

ICMP router discovery

ICMP sourse-quench

CCNA2 Module8

CCNA2 M8 TCIPIP Error Control Messages

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