Hi Again, Thank you ww and RaphaelL for your messages. Comparing the working sites and the not working one, I noticed following case which I am not sure if it is causing the issue. Note : We have dual ISP (Uplink) secnario . On the Spare Unit, I have WAN 1 and Wan 2  WAN 1 Status is " Failed " Wan 1 IP address is not in the same subnet of spare unit device Public IP (It is in the same subnet of the Primary unit Public IP) Wan 2 Status is " Active "  Wan 2 IP address is the same as spare unut Public IP.    Now in the working site same situation (Dual ISP/Uplink)  The Spare unit WAN 1 IP address is in the same subnet of spare unit public IP address . I guess in the Spare unit the WAN1 IP address and the Public IP address of the spare unit need to be in the same subnet .    Please let me know if you need any further information.   Thank you for your time .   ... View more