What is the rule for core network interface IP Address configuration?

[Brant]

I want to change the IP address to suit the customer's requirements. The target settings is IP Address:169.254.157.55, the target Subnet Mask:255.255.0.0. 

The strange thing is, I can change to 169.254.157.55 and 255.255.255.0, but can't use 255.255.0.0. But I can set 192.168.1.1 and 255.255.0.0. So why 169.254.157.55 and 255.255.0.0 couldn't?

[Michael_A]

Hello,
may be your selection is a adress of a special block of ip-adresses called Zeroconf (https://de.wikipedia.org/wiki/IP-Adresse) see table, only in german wiki (english: https://datatracker.ietf.org/doc/html/rfc3927)
This could be a restriction for your case.

[Marc-Smaak · Accepted solution]

@Brant which version of the systemapps are you using. I discoverred this too in the past and asked to get it changed. I can confirm with V1.20 it is again possible to configure static IP address in the IPv4LL range. We needed this beacuse IPv4LL was not supported before (V1.12) and in systems wich use IPv4LL we needed to configure this hardcoded. This change would cause the IP address to change after update.

If you really want to use IPv4LL just flip the switch and you get an address autoatically