Check that the rate settings for network devices or server's NICs have been set correctly. If you set auto negotiation and fixed full duplex, any auto negotiation recognized as half-duplex will result in an unstable communication state.
Confirmation method
Check the switch state. For a server, use the following command to check its state. Also, check the rate settings between switches not only between the server and switches.
# ethtool eth0 Settings for eth0: Supported ports: [ FIBRE ] Supported link modes: 1000baseT/Half 1000baseT/Full Supports auto-negotiation: Yes Advertised link modes: 1000baseT/Half 1000baseT/Full Advertised auto-negotiation: Yes Speed: 1000Mb/s Duplex: Full snip.. Link detected: yes |