1 © 2003, cisco systems, inc. all rights reserved. ccna 2 v3.0 module 8 tcp/ip suite error and...

1© 2003, Cisco Systems, Inc. All rights reserved.

CCNA 2 v3.0 Module 8 TCP/IP Suite Error and

Control Messages

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Objectives

• TCP/IP error messages

• TCP/IP control messages

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TCP/IP error messages

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Internet Control Message Protocol (ICMP)

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Error Reporting and Error Correction

• ICMP is an error-reporting protocol for IP.

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ICMP Message Delivery

• ICMP messages are encapsulated as data in datagrams in the same way any other data is delivered using IP.

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Unreachable Networks

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Ping

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Detecting Excessively Long Routes

• Whether the actual path includes too many hops or a circular routing path exists, the packet will eventually reach the end of its life, known as its time-to-live (TTL).

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TCP/IP error messages

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ICMP Message Types

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Destination Unreachable Message

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Code Values for Destination Unreachable Messages

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TCP/IP Suite Control Messages

• Control messages are used to inform hosts of conditions such as network congestion or the existence of a better gateway to a remote network.

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ICMP Redirect/Change Requests

The default gateway of the host may need to use a redirect/change request to inform the host of the best path to a certain network.

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Clock Synchronization and Transit Time Estimation

• The ICMP timestamp request message allows a host to ask for the current time according to the remote host.

• The remote host uses an ICMP timestamp reply message to respond to the request.

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Address Mask Requirements

• When a network administrator uses the process of subnetting to divide a major IP address into multiple subnets, a new subnet mask is created.

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Router Discovery Message

• When a host on the network boots, and the host has not been manually configured with a default gateway, it can learn of available routers through the process of router discovery.

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Router Solicitation Message

• A host generates an ICMP router solicitation message in response to a missing default gateway.

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Congestion and Flow Control Messages

ICMP source-quench messages are used to reduce the amount of data lost from congestion.