Diagnostic tools
Ping
The ping command allows you to verify whether a device with a specified address is reachable, and to examine network connectivity.
The ping function is implemented through the Internet Control Message Protocol (ICMP): Table 87 The source device sends an ICMP echo request to the destination device.
Table 88 The source device determines whether the destination is reachable based on whether it receives an ICMP echo reply. If the destination is reachable, the source device determines the following:
○The link quality, based on the numbers of ICMP echo requests sent and replies received.
○The distance between the source and destination, based on the round trip time of ping packets.
Trace route
By using the trace route command, you can trace the Layer 3 devices involved in delivering an IP packet from source to destination to check whether a network is available. This is useful for identification of failed node(s) in the event of network failure.
a.Trace route diagram
The trace route function is implemented through ICMP, as shown in a:
Table 89 The source (Device A) sends a packet with a TTL value of 1 to the destination (Device D). The UDP port of the packet is a port number that will not be used by any application of the destination.
Table 90 The first hop (Device B) (the Layer 3 device that first receives the packet) responds by sending a
Table 91 The source device sends a packet with a TTL value of 2 to the destination device.
Table 92 The second hop (Device C) responds with a
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