Still 255.254.128.0 is a valid subnet.

If I understand correctly, rfc1519 relate to how public ip addresses should be attributed. It does not cover what private subnets you use and you still can such submask (as long as you own the whole /16 for example).

rfc950 explicitly allow for such subnets:

> Since the bits that identify the subnet are specified by a bitmask, they need not be adjacent in the address. However, we recommend that the subnet bits be contiguous and located as the most significant bits of the local address.

and I've heard of them being used (hence the complications and the need for rfc1519 for the public address space).

I'm in favor of closing this issue in favor of issue27860.