Hello @Geeaz ,
You can update the IP configuration for a Network Interface using the "Set-AzNetworkInterfaceIpConfig" PowerShell command as described in below article:
https://learn.microsoft.com/en-us/powershell/module/az.network/set-aznetworkinterfaceipconfig?view=azps-5.8.0
The time to change the IP configuration on a NIC depends on the type of IP address you are going to update:
If you're changing the Public IP address of the NIC, the change is almost immediate after the successful command completion.
If the primary network interface has multiple IP configurations and you change the private IP address of the primary IP configuration, you must manually reassign the primary and secondary IP addresses to the network interface within Windows (not required for Linux). To manually assign IP addresses to a network interface within an operating system, see Assign multiple IP addresses to virtual machines. So this additional time is also considered.
Now, coming back to your setup, when you say you have 2 NICs attached to a load balancer and if one of the NIC goes down during any disasters, you want the other NIC to take over the load - If this is regarding the frontend IP of the load balancer, you can also look into Availability Zones, if you are using a Standard Load balancer. You can use Standard Load Balancer to increase availability throughout of your scenario by aligning resources with, and distribution across zones. In a region with Availability Zones, a Standard Load Balancer can be zone-redundant. This traffic is served by a single IP address. A single frontend IP address will survive zone failure. The frontend IP may be used to reach all (non-impacted) backend pool members no matter the zone. One or more availability zones can fail and the data path survives as long as one zone in the region remains healthy.
Please refer : https://learn.microsoft.com/en-us/azure/load-balancer/load-balancer-standard-availability-zones
Kindly let us know if the above helps or you need further assistance on this issue.
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