Re: change to deprecate broadcast on host 0 of a subnet

From: Bjoern A. Zeeb <>
Date: Wed, 15 Sep 2021 15:57:34 UTC
On 12 Sep 2021, at 15:25, Mike Karels wrote:

> Long ago (4.2BSD), the IP broadcast address was the lowest address on 
> a
> network, the one with a host part of 0.  In RFC1122, the broadcast 
> address
> was standardized using a host part of all ones.  4.3BSD changed its
> default, and made the broadcast address settable with ifconfig.  
> However,
> FreeBSD *still* broadcasts packets sent to the lowest address on a 
> subnet.
> I have a change in review to stop broadcasting the lowest address on a
> subnet by default, but added a sysctl to revert to the current 
> behavior.
> I really doubt that anyone is still using a 0-based broadcast address.
> This change allows host 0 on a subnet to be used as an assigned host
> address, as long as the systems on that network support it (including
> routers).  Linux already has this change.
> The review is  See also
> https:/ and

I think it is:

> some of the discussion in
> Comments are welcome on the review.  I will wait a couple of days
> for comments before proceeding.  I am also interested in comments on
> whether this should be MFC'ed to 13-stable after a suitable delay.

I would have even gone one further step back and put this under 
in HEAD and wait until this draft has gone anywhere but with your sysctl 
I think
it is fine (from reading the email not the recent review).

I would prefer if the current behaviour stayed default (would also MFC 
and then flip if this will indeed go anywhere.

My personal note on this is: it is riding a dead horse, driven by 
and it feels 30 year too late to still do this and change this historic