XenServer stay in Disabled state after rebooting, after a while it got disconnected from pool

XenServer stay in Disabled state after rebooting, and after a while it got disconnected from pool. Try to enable host by CLI, it reports "Pool Master is unreachable" root@test-xs xe host-enable host=test-xs Seen from /var/log/xensource.log like below: Mar 16 11:28:48 test-xs xapi: debug||0...