Invalid subnet masks

[Matt Churchyard]

Hello,

Just been helping someone on the forums who appears to have configured their network interface incorrectly. It looks like they've assigned 250.250.250.0 as the netmask.
I've tried assigning this netmask on a 10.1 machine and ifconfig happily accepts it.

Is there any reason why FreeBSD accepts this value as a netmask? I'm fairly well versed in IPv4, although not a real expert, but I see no reason why such a mask would be used.

Testing on my Win8.1 workstation, it gets rejected telling me the mask must be contiguous (i.e. all 1's then 0's), as I would expect.

Regards,
Matt Churchyard