This is not how MX HA works. Both units need individual connections to the internet, you can not share one IP on both appliances. Two/three solutions come to mind: 1) use a separate IP for the second MX 2) Use a different ISP on the spare MX, that could be e simple LTE-router just for dashboard connectivity, and in case of primary MX failure, you connect the primary ISP to the second MX 3) Use the second MX as a cold spare
... View more