[Gllug] DHCP & DNS

[Ian Northeast]

David Damerell wrote:
> 
> On Friday, 7 Dec 2001, Ian Northeast wrote:
> >There is an RFC which states this but it is out of date. There is no
> >such thing as a network class any more and any network number can be
> >used with any network mask (as long as you stay out of the multicast
> >etc. ranges). So using 192.168/16 or 10.x.x/24 are both perfectly valid.
> 
> But note that this is not what I was suggesting; 192.168.0.0/16 has
> the dubious distinction of being an even stupider pick for a home
> network than 192.168.0.0/24.

No, I appreciate that and I certainly wouldn't use 192.168/16 for
anything, I was just using it as a (probably bad) example of classless
subnetting.

> [Also, I see nothing wrong with the continued use of the terms 'class
> A, B, C' to refer to /8, /16 and /24 networks - wherever in the
> address space they are.]

I find that people are getting confused by classless addresses because,
I think, of continued reference to network classes in supposedly
reputable documentation. A colleague had a problem the other day when he
was given two addresses, something like x.y.z.24 and x.y.z.152, for
different (as in ethernet and token ring) interfaces on the same machine
he was installing. These are /25 so they are in distinct networks but he
had trouble getting his head round this. After I explained it (twice,
not particularly well the first time I'm afraid) and pointed him at
Stevens, he showed me the course notes from an IBM TCP/IP course he
attended relatively recently (about 2 years ago I think). After reading
the supposedly authoritative information therein, I could understand his
confusion. 

I think that if we avoid the use of network classes completely and just
use the "/<bits>" terminology people will get more used to the idea that
netmasks do not have to contain a multiple of 8 bits.

It's a pity about the implementation of in-addr.arpa domains in DNS:) I
know there's a way round it but elegant it is not.

Regards, Ian

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