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Re: etherconf or ifupdown problem with subnets



On Sun, Jul 14, 2002 at 03:03:19AM -0500, Carlo U. Segre wrote:

> Hello All:

> I have run across an odd problem when using etherconf in woody to
> configure IP addresses statically on a 128 number subnet.

> I have a subnet which goes from 164.54.244.0 to 164.54.244.127

> When I use etherconf I tell give the mask as 255.255.255.128 but etherconf
> does not ask for a broadcast address, nor does it put one in
> /etc/network/interfaces.

> when the interface is brought up by /sbin/ifup, the broadcast address is
> incorrectly set to 164.54.255.255

> This causes some huge problems on my network and I have had to remove
> etherconf and just edit the /etc/network/interfaces by hand.

> BTW, if the netmask is 255.255.255.0 all works perfectly!

> I don't know if I should report this as a bug to etherconf or ifupdown, or
> even ifconfig.  In the first case, it would be good to have a "broadcast"
> line in /etc/network/interfaces but that might just be masking a problem
> in ifupdown's calculation of a broadcast address from the netmask.  Or
> perhaps it is a problem in ifconfig.  The final possibility is that I am
> making a stupid mistake.

If I list both the netmask and the broadcast explicitly in
/etc/network/interfaces for my /25 network (which is in a class-A
netblock), then the interface is configured correctly.  If I omit one or
the other, then the default class-A value is used.  This seems
reasonable to me; if the netmask or broadcast address should be derived,
it should be done at the kernel level for you -- not in the userspace
tools.  But this is not done, presumably for those rare cases when
someone deliberately wants to have mismatched values...

Steve Langasek
postmodern programmer

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