Device configuration review
Routing tables
Interface status
VLAN assignment
Network performance baselines
Collisions
Broadcast storm
Duplicate MAC address
Duplicate IP address
Multicast flooding
Asymmetrical routing
Switching loops
Routing loops
Rogue DHCP server
DHCP scope exhaustion
IP setting issues
Missing route
Low optical link budget
Certificate issues
Hardware failure
Host-based/network-based firewall settings
Blocked services, ports, or addresses
Incorrect VLAN
DNS issues
NTP issues
BYOD challenges
Licensed feature issues
Network performance issues