1. 1 © 2004, Cisco Systems, Inc. All rights reserved. CCNA 2 v3.1 Module 8 TCP/IP Suite Error and Control Messages

2. 222 © 2004, Cisco Systems, Inc. All rights reserved. Objectives

3. 333 © 2004, Cisco Systems, Inc. All rights reserved. Internet Control Message Protocol (ICMP)

4. 444 © 2004, Cisco Systems, Inc. All rights reserved. Error Reporting and Error Correction ICMP is an error-reporting protocol for IP.

5. 555 © 2004, 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.

6. 666 © 2004, Cisco Systems, Inc. All rights reserved. Unreachable Networks

7. 777 © 2004, Cisco Systems, Inc. All rights reserved. Ping

8. 888 © 2004, 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).

9. 999 © 2004, Cisco Systems, Inc. All rights reserved. ICMP Message Types

10. 10 © 2004, Cisco Systems, Inc. All rights reserved. Destination Unreachable Message

11. 11 © 2004, Cisco Systems, Inc. All rights reserved. Code Values for Destination Unreachable Messages

12. 12 © 2004, 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.

13. 13 © 2004, 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.

14. 14 © 2004, 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.

15. 15 © 2004, 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.

16. 16 © 2004, 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.

17. 17 © 2004, Cisco Systems, Inc. All rights reserved. Router Solicitation Message A host generates an ICMP router solicitation message in response to a missing default gateway.

18. 18 © 2004, 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.

19. 19 © 2004, Cisco Systems, Inc. All rights reserved. Summary