1. © 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 1 Basic routing Ping! Ping! Ping! illustrated

2. Presentation_ID 2 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential What is your level of understanding for ping? 0510

3. Presentation_ID 3 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential What kinds of “ping” results have you seen? A. !!!!! B..!!!! C. U.U.U D..U.U. E. ….. ! = echo reply received. = timeout U = destination unreachable

4. Presentation_ID 4 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential All answers are correct! Unreachable x3 timeout x2 ICMP echo-reply received x4 Timeout x5

5. Presentation_ID 5 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Why “.!!!!”  You may see this kind of result when ping some IP in the first time  Why?  Is it a system bug? Or performance issue?

6. Presentation_ID 6 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Why do you say “ARP”? We need evidence!! “.!!!!”

7. Presentation_ID 7 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential U.U.U Unreachable x3 timeout x2

8. Presentation_ID 8 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential U.U.U Unreachable x3 timeout x2 Why not Timeout x5 ? Why not Unreachable x5 ? Is there any issue?

9. Presentation_ID 9 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential ICMP packet is generated by router CPU “show process cpu history”

10. Presentation_ID 10 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential ICMP packet is generated by router CPU  In this demo, I will: –Disable “rate-limit” for ICMP unreachable packet –Find the ways to change “U.U.U” to “UUUUU” “U….U” “…..”

11. Presentation_ID 11 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Protect your router by disabling ICMP unreachable After apply “no ip unreachables”

12. Presentation_ID 12 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Why we need ICMP unreachable  Source can not know if destination are reachable or not –May not able to trace route –Can’t terminate “unreachable” connection rapidly

13. Presentation_ID 13 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential “ping” results A. !!!!! --congratulations, seems fine B..!!!! -- don’t worry, just ping again C. U.U.U – possible routing issue D..U.U. – possible routing issue E. ….. -- …… ! = echo reply received. = timeout U = destination unreachable

14. Presentation_ID 14 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Some useful commands  ping repeat  debug arp  debug ip icmp / undebug all  ip icmp rate-limit unreachable  ip unreachables (interface mode)  show processes cpu history  “ctrl+shift+6, then x”

15. Presentation_ID 15 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Curriculum reference  CCNA exploration 2 –Chapter 1: introduction for routing and packet forwarding

16. Presentation_ID 16 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential More resources  Using the Extended ping and Extended traceroute Commands –http://www.cisco.com/en/US/tech/tk365/technologies_tech_ note09186a0080093f22.shtmlhttp://www.cisco.com/en/US/tech/tk365/technologies_tech_ note09186a0080093f22.shtml  ICMP Unreachable Rate Limiting User Feedback –http://www.cisco.com/en/US/docs/ios/12_2sb/feature/guide/sbip icmp.htmlhttp://www.cisco.com/en/US/docs/ios/12_2sb/feature/guide/sbip icmp.html