ccna2 m8 tcipip error control messages
TRANSCRIPT
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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