The symptoms
that you see in the network can be the result of problems in another area or layer.
Before jumping to conclusions, try to verify in a structured way what is working and
what is not. Because networks can be complex, it is helpful to isolate possible problem
domains. One way to do this is to use the OSI seven-layer model. For example: Check
the physical connections involved (Layer 1), check connectivity issues within the
VLAN (Layer 2), check connectivity issues across different VLANs (Layer 3), and so
on. Assuming that the switch is con?¬?gured correctly, many of the problems you
encounter will be related to physical layer issues (physical ports and cabling).
?– Do not assume a component is working without ?¬?rst verifying that it is: If a PC is
not able to log into a server across the network, it could be due to any number of things.
Do not assume basic components are working correctly without testing them ?¬?rst;
someone else might have altered their con?¬?gurations and not informed you of the
change. It usually takes only a minute to verify the basics (for example, that the ports
are correctly connected and active), and it can save you valuable time.
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