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Re: etherconf or ifupdown problem with subnets

On Sun, Jul 14, 2002 at 11:41:03PM -0500, Carlo U. Segre wrote:
> But the behavior that I observed is that if the netmask is set up for a
> class C, then the broadcast address is correct (xxx.yyy.zzz.255).  If I
> have a subnet, such as the one in the example (xxx.yyy.zzz.128), the
> broadcast is configured for a class B (xxx.yyy.255.255) rather than the
> correct value (xxx.yyy.zzz.127).  This raises several inconsistencies:

Then it sounds to me like something is incorrectly setting the broadcast
when using a /24 netmask.

> 1. If the correct behavior is to use a class A broadcast, why is the class
> C domain correctly set up and why does the machine in my example have a
> class B boradcast?

The particular network numbers you cited were in the class-B range, not
in the class-A range, were they not?  Therefore, the kernel will default
to using a class-B broadcast.

> 2. If the broadcast address is supposed to be explicitly in the
> /etc/network/interfaces file for reliable operation, shouldn't etherconf
> ask what broadcast address to use and insert it in the file?

If etherconf is a front-end config tool for /etc/network/interfaces
(I don't use it myself), I would argue the correct behavior is to
automatically calculate the broadcast address and set it appropriately,
without prompting the user.  Deliberate netmask/broadcast mismatches are
rare enough that the option should be hidden from those using
configuration tools.

> The way it is working now makes it impossible to use etherconf for static
> IP configuration of anything but class C (or maybe A and B too).  My
> thought is to file a bug against etherconf.

That sounds reasonable.

Steve Langasek
postmodern programmer

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