Re: LAN IP addresses

Moe Trin a écrit :

By the way, there is nothing sacred about the "zero" address, and
some operating systems specifically do allow use of the "network"
address as a _host_ address.

RFC 1812 states otherwise in § 4.2.2.11, 4.2.3.1, 5.3.5.

Perhaps the word "sacred" is to strong. None the less with the advent
of CIDR, the meaning of the "network" and "broadcast" address can not
be known to outsiders,

Wasn't this true already with subnetting, even before CIDR ?

But then, a lot of people misinterpret RFC1122 Section 3.2.1.3 on
page 31 (third paragraph below (g)) as prohibiting a zero (or -1
which they don't understand) in any host part.

Hey, I interpret this paragraph this way too ! :-o
I quote it for completeness :

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).

To me it clearly means that the host number part of a unicast host address cannot be 0. What I am reading wrong ?

If such an address is used, it must be treated as a broadcast and
cannot be used as a host address.

The "network" address has not been used as a broadcast address for a
long time - 4.2BSD was replaced by 4.3 a bit over twenty years ago.

Anyway at least one modern OS, Linux, still interprets it as an alternate directed broadcast address.
.

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