Forcing static address in 12.04

Karl Auer kauer at biplane.com.au
Wed Jun 10 23:53:53 UTC 2015


On Wed, 2015-06-10 at 15:11 -0700, rikona wrote:
> Also learned that .233 is used as a broadcast address. Didn't know
> that - I've been using it for a number of years on several boxes and
> it always 'just worked'. :-) IIRC it was a default in older Netgear
> routers; worked, so kept using it. But I now see that .255 might be
> better for an actual broadcast address.

Um, .233 is not a broadcast address. It depends completely on the
network size as to what the broadcast address in a given subnet is. For
your subnet, 192.168.144.0/24, .255 is the broadcast address, but you
were telling your system that it was .233, which was certainly a
mistake. Now corrected.

The broadcast address in an IPv4 subnet is simply the address with all
the host bits set to 1. So for a 24-bit subnet a.b.c.0/24 (netmask
255.255.255.0) the broadcast address is is a.b.c.255. This is the setup
in almost all home networks. For a 30-bit subnet, like a.b.c.0/30
(netmask 255.255.255.252), the broadcast address would be a.b.c.3. There
are 64 30-bit subnets in one 24-bit subnet:

   a.b.c.0/30 netmask a.b.c.3
   a.b.c.4/30 netmask a.b.c.3
   a.b.c.8/30 netmask a.b.c.3
   a.b.c.12/30 netmask a.b.c.3
   ...

233 is 11101001 in binary, so it's not a modern netmask for any sized
network; modern netmasks are contiguous sequences of 1-bits.

Regards, K.

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Karl Auer (kauer at biplane.com.au)
http://www.biplane.com.au/kauer
http://twitter.com/kauer389

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