Hi,

at work I am "forced" to work with hp-ux ( which is, IMHO, one of the
worst unix implementations I ever worked with. But I don't want to
talk about this right now :-). Starting from version 10.x they forbid
the following netmask: 255.255.255.128 for a class C IP-Address (eg.
192.13.13.13).
When I called hp-support they said that this netmask was illegal, citing
rfc-1122 (well, they also offered me a workaround, because other
customers had complained about this as well :-). Reading through
rfc-1122 I found the following passage (page 30):

...
            IP addresses are not permitted to have the value 0 or -1 for
            any of the <Host-number>, <Network-number>, or <Subnet-
            number> fields (except in the special cases listed above).
            This implies that each of these fields will be at least two
            bits long.

where -1 means all bits one and the special cases are just broadcast and
initialisation addresses.

Can anybody explain why this was done?

And my second question: Do we comply to this standard?
Although I can see no reason for the requirement, we should comply
and offer a variable which can be set by sysctl to turn this behaviour
on or off.

  Guenther