Set static IP address

There’s no supported way to programmatically set a static IP address. Why do you want to this?

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—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

so I‘d like to do it programmatically.

AFAIK nothing has changed in this space. There is certainly no way, on iOS, to modify the TCP/IP configuration of a wired Ethernet interfaces.

This device picks a random IP un the 169.254.x.x network.

By “device” do you mean the iOS device? Or your accessory?

If your accessory is choosing a self-assigned IPv4 address [1] then you shouldn’t need to configure a static IP address on the iOS device. By default it will choose a similar self-assigned IPv4 address and that’ll allow you to communicate.

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—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

[1] Per RFC 3927 Dynamic Configuration of IPv4 Link-Local Addresses.