Network Diagnostics

The Network Diagnostics group gathers the four system commands that measure whether a target is reachable over the network, with how much latency and through which path it is reached. They are the commands that are looked at first in situations such as a backend appearing as down in the health check, the VIP not being reachable from outside, or a slowness complaint.

ping

Is a single IPv4 target reachable, and how much are the latency and the loss?

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ping6

The same measurement, for IPv6 targets.

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traceroute

Through which intermediate points does the packet pass to the target, and where does it stop?

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fping

Many targets or a subnet are probed in a single command.

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Which Command When?

Question	Command	Example
Is the backend reachable from the network, and how many ms is the latency?	ping	sys-cmd ping -c 4 10.20.0.15
Is a target with an IPv6 address reachable?	ping6	sys-cmd ping6 -c 4 2001:db8::15
There is no access; where on the way is the packet lost?	traceroute	sys-cmd traceroute -n 10.20.0.15
Which of the servers in a backend group are up?	fping	sys-cmd fping -c 3 10.20.0.15 10.20.0.16
Which addresses in a subnet respond?	fping	sys-cmd fping -a -g 10.20.0.0/24

An ICMP response alone is not enough

These four commands use ICMP. If the target responds but the service is not working, the problem is not in the network but in the service port; the next step is a test at the port level: nmap, telnet or curl. Conversely, a target behind a firewall that blocks ICMP may have a working service even though it does not respond.

Common Behavior

Subject	Behavior
Writing	All four are tools with free parameters: everything written after the command name is passed to the tool as it is.
Context	The measurement is made from within the v-device and the route table selected in WEB-CLI. For a target in an isolated route table, route-table set is run first.
Duration	ping and ping6 run without stopping if a packet count is not given; they are limited with -c or stopped with Ctrl+C. traceroute and fping close by themselves when they finish their work.
Pipe	The output can be filtered with | or written to a file with to-file.
Recording	Every run is written to the user logs.

All of the writing rules, the restrictions and the stopping behavior: System Commands.