Forcing static address in 12.04

rikona rikona at sonic.net
Thu Jun 11 03:31:42 UTC 2015


Hello Karl,

Wednesday, June 10, 2015, 4:53:53 PM, Karl wrote:

> 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.

So much for the reliability of an inet blog comment. :-) I ran across
it when I was looking for the address fix. Didn't end up using what
that blog suggested anyway - others were more clear and I used those
instead.

> 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.

That was just for the example format I used the last time, and yes, I
can now see that was not proper. That blog just said 'use this' and
didn't say why each item was selected.

> Now corrected.

Actually, looks like I did not need to input that anywhere in the
final setup.

> 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.

Makes sense - thanks for the very clear description!

-- 

 rikona        




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