On 2024-06-12 00:47, Poul-Henning Kamp wrote:
I had a machine with this line in /etc/rc.conf:ifconfig_bla0="192.168.87.11" I found out the hard way, that this defaults to /8 now. The main symptom was that DNS was /really/ busted, which makes sense when none of the DNS servers in the 192/8 "swamp" can be reached. Since we all know that it is always DNS(SEC), I spent a lot of time having fun with that, before I noticed the /8 netmask on the interface. I agree that the class A/B/C netmask assumptions should have died long ago. But from a foot-shooting point of view, it makes no sense to default 192.168/16 to a /8 netmask. If we're going to default to /8, at the very least ifconfig should spitting out a very noisy warning and wait 5 seconds before proceeding, when the netmask is not explicitly specified. But I also think we can do better than /8. One option is to go for "limit the damage in RFC1918" and default them according to their size: reach: 10/8 172.16/12 192.168/16 That will prevent the DNS weirdness I had to figure out, and probably still DWIM in most cases. Another option is to default all three to /24, which in my experience is how people deploy RFC1918. A third option is to default any missing netmask to /24 instead of /8, which would be what I would personally have done in the first place.
I couldn't agree more. CPEs, WiFi AP's and most other network(ing) equipment that most users encounter, generally default to a /24 (255.255.255.0). IMHO this would result in the least amount of POLA. :)
Poul-Henning
--Chris
