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1© 2003, Cisco Systems, Inc. All rights reserved.
CCNA 2 v3.0 Module 8 TCP/IP Suite Error and
Control Messages
444© 2003, Cisco Systems, Inc. All rights reserved.
Objectives
• TCP/IP error messages
• TCP/IP control messages
555© 2003, Cisco Systems, Inc. All rights reserved.
TCP/IP error messages
666© 2003, Cisco Systems, Inc. All rights reserved.
Internet Control Message Protocol (ICMP)
777© 2003, Cisco Systems, Inc. All rights reserved.
Error Reporting and Error Correction
• ICMP is an error-reporting protocol for IP.
888© 2003, Cisco Systems, Inc. All rights reserved.
ICMP Message Delivery
• ICMP messages are encapsulated as data in datagrams in the same way any other data is delivered using IP.
999© 2003, Cisco Systems, Inc. All rights reserved.
Unreachable Networks
101010© 2003, Cisco Systems, Inc. All rights reserved.
Ping
111111© 2003, Cisco Systems, Inc. All rights reserved.
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).
121212© 2003, Cisco Systems, Inc. All rights reserved.
TCP/IP error messages
131313© 2003, Cisco Systems, Inc. All rights reserved.
ICMP Message Types
141414© 2003, Cisco Systems, Inc. All rights reserved.
Destination Unreachable Message
151515© 2003, Cisco Systems, Inc. All rights reserved.
Code Values for Destination Unreachable Messages
161616© 2003, Cisco Systems, Inc. All rights reserved.
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.
171717© 2003, Cisco Systems, Inc. All rights reserved.
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.
181818© 2003, Cisco Systems, Inc. All rights reserved.
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.
191919© 2003, Cisco Systems, Inc. All rights reserved.
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.
202020© 2003, Cisco Systems, Inc. All rights reserved.
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.
212121© 2003, Cisco Systems, Inc. All rights reserved.
Router Solicitation Message
• A host generates an ICMP router solicitation message in response to a missing default gateway.
222222© 2003, Cisco Systems, Inc. All rights reserved.
Congestion and Flow Control Messages
ICMP source-quench messages are used to reduce the amount of data lost from congestion.