(R720)iDRAC does not work with dedicated NIC

I have got a Dell PowerEdge R720 which has a right Enterprise Lisense of iDRAC.The dedicated iDRAC NIC does not work weather it‘s in DHCP mode which would not get any IP address nor it’s in static mode.In a nutshell,it doesn‘t work.I've tried a lot of things to fix the problem.Not noly did I replace the Ethernet cable and switch but also I reflash both iDRAC and BIOS with the latest firmware from official support website.Last but not least,iDRAC works pretty well with the LOM,but I really want access iDRAC with its dedicated NIC.I would be extremely grateful if you could solve my problem.