Re: (PM) IP Pool

Scott Carpenter (scarpenter@assuredaccess.com)
Thu, 08 Jan 1998 09:57:16 -0800

At 09:46 PM 1/7/98 -0700, Stephen Fisher wrote:
>
>Um.. actually this is how I understand it:
>
>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 :-)
Cisco's implimentation is a little different:

if you have router A useing 192.168.1.1/26 (e0) running (isdn) unnumbered
to router B 192.168.1.65/27 not running any rp (ie.
ospf/is-is/ripv2/bgp4/static). You are relying on the default gateway. in
the cisco implimentation you will have to turn on ip classless for any
hosts on router B to to reach hosts on router A.

Now if you are running one of the above protocols vlsm/cidr will work fine.

if you are not running a protocol above and relying on the default gateway
you will have to enable ip classless.

>
>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:
>> >
>> >-
>> >To unsubscribe, email 'majordomo@livingston.com' with
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>>
>
>--
> - Steve
> - Systems Manager
> - Community Internet Access, Inc.
> - Gallup and Grants, New Mexico
>-
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>
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