[c-nsp] VLSM

[Stephen J. Wilcox]

no no no no it absolutely is not! read rfc1812

<rant>
to be a Class B,

1) our routers must be operating in classful mode (no ip classless) which 
changes the behaviour of routing

2) the first two bits of the ip address must be 1-0

i may be given the netblock 172.13.14.0/24... the first two bits are 1-0 
therefore by rfc796 it must be class b network 172.13.0.0 using a subnet of 
255.255.255.0 creating 256x 172.13.x.y networks - clearly not true

alternatively i may have 195.0.0.0/16 .. as it is a /16 it must be class B, but 
class B must start 1-0 and this starts 1-1 .. in fact according to rfc796 it is 
in class C space so i must be talking about 256x Class Cs - this is actually 
what you say below. but this is also untrue because i have taken the /16 and i 
have split it into 4x /18s each of which is a single lan subnet eg 
195.0.64.0/255.255.192.0 with default gateway 195.0.127.254 .. in fact i may 
wish to assign my computer the ip 195.0.100.255/18 -- something which is 
reserved according to rfc796 as a broadcast address

do you see how none of this can work when we start mixing the logic of classful 
network and classful behaviour with classless?

Steve

On Tue, 11 Jan 2005, Anson Rinesmith wrote:

> Actually according to the RFC, Class B and /16 (16-bit local address) are
> the same thing...
> 
> "The second type (or class b) of address has a 14-bit network number and a
> 16-bit local address."
> 
> If you have a /16 (or class b), and give me anyone 1 IP in that range, I can
> tell you the beginning and ending IP of that range, otherwise it is just a
> group of Class C's.
> 
> 
> 
> > -----Original Message-----
> > From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-
> > bounces at puck.nether.net] On Behalf Of lists at hojmark.org
> > Sent: Tuesday, January 11, 2005 4:25 PM
> > To: 'Hudson Delbert J Contr 61 CS/SCBN'; 'matthew zeier'; 'Gert Doering';
> > 'Shaun'
> > Cc: cisco-nsp at puck.nether.net
> > Subject: RE: [c-nsp] VLSM
> > 
> > > since when is a /16 size chunk of addresses not a class 'b'
> > > space.
> > 
> > It's only class B if the first two bits are 10, otherwise it's a just
> > block
> > of addresses the same size as an old class b. Check out
> > http://rfc.sunsite.dk/rfc/rfc796.html
> > 
> > ... But why not simply call it "a /16", since that's what it is?
> > 
> > > i think what manner in which the size of a space is called as
> > > long as one understands what it speak of. much ado about
> > > nothing methinks.
> > 
> > OK. I'll just call you Peter then, though that's not your name. It doesn't
> > really matter as long as people know I mean you ;-)
> > 
> > -A
> > 
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