Misconfigured switch port
Layer 2 access control lists
Misconfigured Spanning Tree Protocol
Missing or misconfigured VLANsAt Layer 3 (the Internet layer), IP connectivity and
reachability have to work. The network client should be
configured with the correct IP address, subnet mask, and
default gateway. This is usually done using DHCP
servers, and in rare cases it may be manually configured.
Built-in operating system tools such as ifconfig and
ping can be used at this layer to help with
troubleshooting. ifconfig (or ipconfig on Microsoft
Windows) is a network utility that retrieves and can
modify the configuration and status of all network
interfaces present on the client endpoint. ping is another
popular network tool that is extensively used to verify
endpoint IP reachability. If the destination of the client
data traffic is in a different subnet than the client is
connected to, that means that the traffic has to be routed
through the default gateway of the client subnet. Layer 3
connectivity between data traffic source and destination
can be checked using the ping command. If IP
connectivity is verified end to end between source and
destination, troubleshooting can proceed to the next
step. If not, you need to look for the problems that can
cause connectivity issues at Layer 3, including these:
Misconfigured IP information (IP address, subnet mask, default
gateway) on the client device
Layer 3 access control lists that blocks data traffic
Routing protocol issues causing black-holing or incorrect routing of
traffic