BFD is configured between the NE80E-1 and NE80E-2. The BFD configuration of the NE80E-1 lacks the commit command. The NE80E-1 needs to redeliver the configuration after being upgraded and restarted. If the BFD configuration lacks the commit command, the system cannot send BFD packets and the BFD session is always Down, which results in the Down of Eth-Trunk. The BFD session is Up before the upgrade and down after the upgrade, because the BFD configuration is modified after the session is Up and the commit command is not entered to make the modified configuration take effect. Instead, you directly exit the BFD configuration mode and system.