From: Tom Lijnse (Tom.Lijnse@globalknowledge.nl)
Date: Wed Jun 29 2005 - 07:02:29 GMT-3
Hi Gene,
Let's quote from RFC 1812 (Requirements for IP Version 4 Routers) page
22:
" The classical IP addressing architecture used addresses and subnet
masks to discriminate the host number from the network prefix. With
network prefixes, it is sufficient to indicate the number of bits in
the prefix. Both representations are in common use. Architecturally
correct subnet masks are capable of being represented using the
prefix length description. They comprise that subset of all possible
bits patterns that have
o a contiguous string of ones at the more significant end,
o a contiguous string of zeros at the less significant end, and
o no intervening bits.
Routers SHOULD always treat a route as a network prefix, and SHOULD
reject configuration and routing information inconsistent with that
model."
Formally RFC 1812 is not STD (Standard), but only a Proposed Standard.
For all practical purposes though this is a standard, in the sense that
any router vendor will stick to these rules, because otherwise their
routers would not really work with anybody else's routers. (Many things
we typically refer to as "standards" really aren't formally full
standards yet. For example BGPv4 (RFC 1771) is only a Draft Standard, so
it really comes down to how strict you want to be when you use the word
'standard').
RFC 950 (Internet Standard Subnetting Procedure), which is actually a
formal Standard (STD), still allows for non-contiguous subnet masks.
So only in the strictest possible sense this 'networkers urban legend'
is true. (And since Cisco adheres to RFC 1812, you definitely won't have
to deal with those strange non-contiguous subnet masks on the lab).
Regards,
Tom Lijnse
CCIE #11031
Global Knowledge
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Gene Thorne
Sent: zaterdag 25 juni 2005 23:53
To: ccielab@groupstudy.com
Subject: RE: Subnet Question? Help
I always thought it would be cool to have a mask like 255.255.255.1.
Then
you would have all the odd addresses on one subnet and the even
addresses on
another. :-) I've heard that the standards don't actually forbid this.
(That
may be a networker's urban legend, I haven't personally checked it out.)
But
even if the standards permit no one implements these non-contiguous
masks
because of the reasons y'all have stated. It'd be fun though wouldn't
it?
-gt
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Scott Morris
Sent: Saturday, June 25, 2005 2:52 PM
To: 'Joe Smith'; DBrowning@Everlogic.com; oletu@inbox.lv;
Dirk.Stewart@co.fulton.ga.us; ccielab@groupstudy.com
Subject: RE: Subnet Question? Help
Fortunately, for everyone's else's brain cells and the programmers
hairlines, you weren't on the committee to come up with the concepts of
subnetting! (smirk)
Mathematically, it will work, however it's a REALLY bad idea, and the
router
knows this. ;)
Scott
-----Original Message-----
From: Joe Smith [mailto:j333smith@hotmail.com]
Sent: Saturday, June 25, 2005 3:06 PM
To: swm@emanon.com; DBrowning@Everlogic.com; oletu@inbox.lv;
Dirk.Stewart@co.fulton.ga.us; ccielab@groupstudy.com
Subject: RE: Subnet Question? Help
Scott,
In my opinion it logically works. It is much more difficult for us
non-CPU
units to decipher; and I think it would kill supernetting as we know it.
172.16.26.49 255.255.50.0 where 50 is 00110010 in binary. Below "x"
represents 0-255.
Subnet 172.16.0.0
Hosts 172.16.1.x, 172.16.4.x, 172.16.5.x, 172.16.8.x, 172.16.9.x,
172.16.12.x, 172.16.13.x, 172.16.64.x, 172.16.65.x, 172.16.68.x,
172.16.72.x, 172.16.73.x, 172.16.76.x, 172.16.77.x, 172.16.128.x, etc.
Broadcast 172.16.205.255
Subnet 172.16.2.0
Hosts 172.16.3.x, 172.16.6.x, 172.16.7.x, 172.16.10.x, 172.16.11.x,
172.16.14.x, 172.16.15.x, 172.l6.66.x, etc.
Broadcast 172.16.207.255
Subnet 172.16.16.0
Hosts 172.16.17.x, 172.16.20.x, 172.16.21.x, 172.16.24.x, 172.16.25.x,
172.16.30.x, 172.16.31.x, 172.16.80.x, etc.
Broadcast 172.16.221.255
Subnet 172.16.18.0
Hosts 172.16.19.x, 172.16.22.x, etc.
Broadcast 172.16.223.255
Subnet 172.16.32.0
Hosts 172.16.33.x, 172.16.36.x etc
Broadcast 172.16.237.255
Subnet 172.16.34.0
Hosts 172.16.35.x, 172.16.38.x, etc.
Broadcast 172.16.239.255
Subnet 172.16.48.0
Hosts 172.16.49.x, 172.16.52.x etc.
Broadcast 172.16.253.255
Subnet 172.16.50.0
Hosts 172.16.51.x, 172.16.54.x, etc.
Broadcast 172.16.255.255
>From: "Scott Morris" <swm@emanon.com>
>Reply-To: "Scott Morris" <swm@emanon.com>
>To: "'Darren Browning'" <DBrowning@Everlogic.com>, "'Godswill Oletu'"
><oletu@inbox.lv>, "'Stewart, Dirk'" <Dirk.Stewart@co.fulton.ga.us>,
><ccielab@groupstudy.com>
>Subject: RE: Subnet Question? Help
>Date: Fri, 24 Jun 2005 16:14:00 -0400
>
>Logically and router-wise, it will not work.
>
>50 = 00110010 as a binary number. Think back to everything from the
>CCNA days. Subnetting is about drawing a line.
>
>Everything on the left of the line is subnet, everything on the right
>of the line is host.
>
>Besides, the router will bitch:
>emanon-R8(config-if)#ip address 172.16.26.49 255.255.50.0 Bad mask
>0xFFFF3200 for address 172.16.26.49 emanon-R8(config-if)#
>
>Things that make you go "Hmmmm...."
>
>;)
>
>Scott
>
>PS. So that means it's bad practice AND impossible reality.
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>Darren Browning
>Sent: Friday, June 24, 2005 4:02 PM
>To: Godswill Oletu; Stewart, Dirk; ccielab@groupstudy.com
>Subject: RE: Subnet Question? Help
>
>Although id agree it's a bad practice to have address 172.16.26.49
>255.255.50.0
>
>But this will work, this gives you 52,736 addresses range's are
>172.16.18.0
>- 172.16.223.255
>
>Cheers
>Daz
>CCIE#7976
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>Godswill Oletu
>Sent: 24 June 2005 20:40
>To: Stewart, Dirk; ccielab@groupstudy.com
>Subject: Re: Subnet Question? Help
>
>it might be error, they likely meant 172.16.26.49/255.255.0.0
>
>255.255.50.0 is a bad subnet mask.
>
>
>----- Original Message -----
>From: "Stewart, Dirk" <Dirk.Stewart@co.fulton.ga.us>
>To: <ccielab@groupstudy.com>
>Sent: Friday, June 24, 2005 3:21 PM
>Subject: Subnet Question? Help
>
>
> > Is this a valid subnet and where and how would I use it. Does ISP
> > use this kind of subnet.. If this is possible how much networks and
> > host could I get from it...
> >
> > 172.16.26.49
> >
> > 255.255.50.0
> >
> >
> > -----------------------------------------------------
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> >
> >
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