Ping - debug commands

When implementing the Ping command to troubleshoot network connectivity and other issues, it can be helpful to use appropriate debug commands to gain further insight into the reasons behind possible ping failures. The operating system you are using will typically provide responses however, you may need more detail.

On a Cisco IOS device, you can use debug commands to obtain a deeper understanding of the reasoning behind failures. You can then lookup the ICMP codes and types that you observe to determine the reason for failure. The following is an example with which debugs have been applied to a series of pings that have failed:

Router1#debug ip packet detail
IP packet debugging is on (detailed)

Router1#ping 172.16.4.34
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.4.34, timeout is 2 seconds:
U.U.U
Success rate is 0 percent (0/5)

Jan 20 16:05:30.659: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100,
  sending
Jan 20 16:05:30.663:     ICMP type=8, code=0
Jan 20 16:05:30.691: IP: s=172.16.0.12 (Serial0), d=172.16.12.1 (Serial0), len 56,
  rcvd 3
Jan 20 16:05:30.695:     ICMP type=3, code=1
Jan 20 16:05:30.699: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100,
  sending
Jan 20 16:05:30.703:     ICMP type=8, code=0
Jan 20 16:05:32.699: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100,
  sending
Jan 20 16:05:32.703:     ICMP type=8, code=0
Jan 20 16:05:32.731: IP: s=172.16.0.12 (Serial0), d=172.16.12.1 (Serial0), len 56,
  rcvd 3
Jan 20 16:05:32.735:     ICMP type=3, code=1
Jan 20 16:05:32.739: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100,
  sending
Jan 20 16:05:32.743:     ICMP type=8, code=0

Notice the varying type and code values that appear in the debugs. Using those values, a more detailed reason for failure can be determined.

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