VLSM - Variable Length Subnet Masks - This IS what actually allows you to
start at any subnet boundary
CIDR - Classless Inter-domain Routing - This is VLSM along with the ability
to do classless routing (using a /24 in Class-A range for example such as
128.214.110.0-.255).
On Cisco routers there is an option to do CIDR - ip classless. VLSM just
works. So.. they're different but they aren't I suppose.. certainly nothing
to be picky about :-)
On Wed, Jan 07, 1998 at 02:20:15PM -0800, Scott Carpenter wrote:
> Stephen,
>
> Here is some RFCs that will clear up some confusion. I will not
> be publicly defaced, especially when I'm right.
>
>
> Scott
>
>
> At 02:00 AM 12/31/97 -0500, Stephen Zedalis wrote:
> >
> >I agree. There were a few problems with Mr. Carpenter's message.
> First,
> >its VLSM, not CIDR that allows you to start at any subnet boundary.
>
> This is from rfc1817:
> >>>>
>
> > Classless Inter-Domain Routing (CIDR) ([RFC1518], [RFC1519]) is
> > deployed in the Internet as the primary mechanism to improve
> > scaling property of the Internet routing system. Essential to CIDR
> > is the generalization of the concept of variable length subnet
> > masks (VLSM) and the elimination of classes of network numbers (A,
> > B, and C). The interior (intra-domain) routing protocols that
> > support CIDR are OSPF, RIP II, Integrated IS-IS, and E-IGRP. The
> > exterior (inter-domain) routing protocol that supports CIDR is
> > BGP-4. Protocols like RIP, BGP-3, EGP, and IGRP do not support
> > CIDR.
> >
> >
> <<<<
>
> The above is saying CIDR is VLSM!
>
> >Second, using a number that is a network number as well as a host
> number
> >will confuse all sorts of machines as Miquel has pointed out. Third,
> its
> >even worse if those numbers think they are on a broadcast network vice
> a
> >PTP link as the broadcast address is used in this setup.
>
> rfc1518 & rfc1519 Will answer the above questions.
>
> >
> >On 30 Dec 1997, Miquel van Smoorenburg wrote:
> >
> >>In article
> <3.0.3.32.19971230105254.006b7ad4@gateway.assuredaccess.com>,
> >>Scott Carpenter <scarpenter@assuredaccess.com> wrote:
> >>>The way I have found works best is if you start the pool at a
> subnett boundry
> >>>such as X.X.X.0 and set the pool size to 48. now remember that we
> are in
> >>>the age of cidr so the .0 is a valid ip address and it is ok if it
> gets
> >>>assigned to a user......
> >>
> >>I wouldn't do that if I were you:
> >
> >-
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>
-- - Steve - Systems Manager - Community Internet Access, Inc. - Gallup and Grants, New Mexico - To unsubscribe, email 'majordomo@livingston.com' with 'unsubscribe portmaster-users' in the body of the message.