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Ping Failure Troubleshooting (1) Highlighted

Latest reply: May 11, 2018 06:52:56 2635 3 0 0 1

Fault Analysis

A ping failure refers to the failure to receive all ping response packets for reasons such as a link fault or ARP learning failure.

To learn about ping mechanisms, see Ping Implementation.

Figure 1-1 shows a network where a ping failure has occurred.

Network where a ping failure occurs



Fault Symptom

Switch A cannot ping switch D.

<SwitchA> ping  
PING 56  data bytes, press CTRL_C to break
    Request time out
    Request time out
    Request time out
    Request time out
    Request time out
  --- ping statistics ---
    5 packet(s) transmitted
    0 packet(s) received
    100.00% packet loss

Description of the ping command output




Ping the host with IP address to check whether the host is reachable.

56  data bytes

Length of the sent Echo Request packet.

press CTRL_C to break

Press Ctrl+C to terminate the ping operation.

Request time out

Displayed when no ICMP Echo Reply packet is received before the timeout period expires. ping statistics

Statistics collected after the ping test on the destination host is complete, including:

l  packet(s) transmitted: indicates the number of sent ICMP Echo Request packets.

l  packet(s) received: indicates the number of received ICMP Echo Reply packets.

l  % packet loss: indicates the percentage of unacknowledged packets against total packets sent.

l  round-trip min/avg/max: indicates the minimum, average, and maximum round-trip delay, in ms. The information is not displayed when a ping operation fails.


Fault Location

In Figure 1-1, a ping operation involves three roles:

l   Source end: switch A, which sends a ping packet.

l   Intermediate devices: switch B and switch C.

l   Destination end: switch D, which receives a ping packet.

If switch A cannot ping IP address, it is difficult to locate the fault cause. In this situation, reduce the fault range. Ping switch B, switch C, and switch D from switch A, ping switch C and switch D from switch B, and so on. Then you can determine which network segment has the problem.

The following are two situations of ping failure locating:

l   Situation 1: If the fault exists between switch A and switch B, that is, switch A fails to ping the IP address of switch B, the fault location process is shown in Figure 1-2 (the handling method for other ping failures on directly connected subnet is the same). For details, see 1.2 Fault Location Methods.

l   Situation 2: If switch A can ping the IP address of switch B, switch B can ping the IP address of switch C, but switch A fails to ping the IP address of switch C, collect ICMP packet statistics on switch A, switch B, and switch C, to determine where the ping packet is discarded. For traffic statistics collection method, see ICMP Statistics Collection.

Ping failure troubleshooting process


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Created May 28, 2017 04:38:43

:)very good
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MVE Created May 2, 2018 05:42:05

useful document, thanks
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Created May 11, 2018 06:52:56

useful document, thanks
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