akobayas@cvbnet.UUCP (Andrew Kobayashi) (09/14/89)
I have a question about the use of 0 as a legitimate sub-network number.
My site is running a Class B address which we have carved up into
Class C subnets for convenience. One of them is subnet 0, that is,
the addresses are XX.XX.0.YY, where XX.XX is our Class B address and
YY is the host number. Things have apparently been running fine for
about eight months.
The question is whether this is "allowed" and (as a separate issue)
whether it is a "good idea", and specifically whether we should change
the subnet number to something else. The concern is apparently with the
use of XX.XX.0.0 as a broadcast address by some IP implementations.
There is no host number 0 on the 0 subnet, but someone with an HP analyzer
on the 0 subnet thought he saw some strange traffic.
We are running a mixture of Suns (on 3.x and 4.0), IBM mainframes, Pixels,
and i'm not sure what else.
It is also possible that i'm completely confused and am not asking the
right question. Any help is appreciated.
--Andrew Kobayashi
Prime Computer (at least that's what they're calling it *this* week.)
<@en-c06.prime.com:akobayas@spica2.prime.com>
{sun,linus,decvax,atexnet}!cvbnet!akobayas
insert standard disclaimer.fin@UF.MSC.UMN.EDU ("Craig Finseth") (09/16/89)
Is is "allowed" (i.e., technically legal)? Undefined. Network number 0 means "this net." By analogy subnet number 0 means "this subnet." You won't find this mentioned anywhere official, that's why it is undefined. Is it a "good idea?" Definite no. It will work mostly, in some circumstances. It is not guaranteed to work "properly." If you look hard enough (or if someone installs some new equipment on Friday afternoon), you will find some equipment that it won't work with I suggest that you ease the users of that subnet to a new one as soon as convenient. BTW, Are you the Andy Kobayashi that I knew from Carolingia? If so, hello. If not, my apologies for the mistake. Craig A. Finseth fin@msc.umn.edu [CAF13] Minnesota Supercomputer Center, Inc. (612) 624-3375 (Cayle of Firwood)
mhw@wittsend.lbp.harris.com (Michael H. Warfield (Mike)) (09/21/89)
In article <8909151911.AA14633@uf.msc.umn.edu> fin@UF.MSC.UMN.EDU ("Craig Finseth") writes: > Is is "allowed" (i.e., technically legal)? >Undefined. Network number 0 means "this net." By analogy subnet >number 0 means "this subnet." You won't find this mentioned anywhere >official, that's why it is undefined. This was discussed some time ago in this news group and it was generally agreed that subnet 0 was prohibitted by RFC 950. Subnet 0 is mentioned in RFC950 as follows: +-------------------------RFC 950 ---------------------------------------+ It is useful to preserve and extend the interpretation of these special addresses in subnetted networks. This means the values of all zeros and all ones in the subnet field should not be assigned to actual (physical) subnets. +-------------------------RFC 950 ---------------------------------------+ It will work in most cases (I know, I'm running one; sigh). However, it is not a good ideas, it should be avoided, and it is technically proscribed. Michael H. Warfield (The Mad Wizard) | gatech.edu!galbp!wittsend!mhw (404) 270-2123 / 270-2098 | mhw@wittsend.LBP.HARRIS.COM An optimist believes we live in the best of all possible worlds. A pessimist is sure of it!
mogul@decwrl.dec.com (Jeffrey Mogul) (09/21/89)
In article <8909151911.AA14633@uf.msc.umn.edu> fin@UF.MSC.UMN.EDU ("Craig Finseth") writes: > > Is it [subnet number = 0] "allowed" (i.e., technically legal)? > >Undefined. Network number 0 means "this net." By analogy subnet >number 0 means "this subnet." You won't find this mentioned anywhere >official, that's why it is undefined. Actually, it is mentioned "somewhere official". From RFC950: [The] values of all zeros and all ones in the subnet field should not be assigned to actual (physical) subnets. The Host Requirements (draft?) RFC more or less reiterates this rule. As an aside: much as it pains me to admit it, in all honesty I have to say that one probably would not run into any real problems by assigning a subnet number = 0. Avoiding subnet 0 is "good engineering practice" more than a result of bitter experience. (That is not the case with assigning a host number = 0, since this looks to some hosts like a broadcast). I make this admission because otherwise people are going to say "I tried using subnet 0, it works, so why the rule?" -Jeff