Wonder if that's part of the reason I didn't make it to day 2 ;->
I see the point of the article, but I still believe it is more of a
compatibility issue than anything else. Can't get into the RFC server I
normally use to see if RFC 1812 ventures an opinion. CIDR probably figures
in here somewhere.
I know that throughout my practice for the lab that I have had situations
exactly as described in the link you provide. I don't recall problems, but
then the lab is not reality ;->
Chuck
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
David Chandler
Sent: Sunday, April 15, 2001 12:42 PM
To: [EMAIL PROTECTED]
Subject: Re: designing subnets with all ones/zeros.. [7:695]
Chuck
Thanks for the proof read :>
Bellow is the cisco page & part of the doc relating to zero subnets.
To me it reads "don't; because we say so"
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_c
/ipcprt1/1cdipadr.htm#xtocid105602
-----------------------
Enabling Use of Subnet Zero
Subnetting with a subnet address of zero is illegal and strongly discouraged
(as
stated in RFC 791) because of the confusion that can arise between a network
and
a
subnet that have the same addresses. For example, if network 131.108.0.0 is
subnetted as 255.255.255.0, subnet zero would be written as
131.108.0.0which is
identical to the network address.
You can use the all zeros and all ones subnet (131.108.255.0), even though
it is
discouraged. Configuring interfaces for the all ones subnet is explicitly
allowed.
However, if you need the entire subnet space for your IP address, use the
following command in global configuration mode to enable subnet zero:
---------------------------
You mentioned that Windows is not rfc1812 compiant and that it allows wacky
subnets and disallows some valid subnets. Was that trial & error or has
microsoft documented this? I hate spending an hour looking for a document
that
is not there...
Thanks
DaveC
Chuck Larrieu wrote:
> Comments within:
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
> David Chandler
> Sent: Saturday, April 14, 2001 11:25 PM
> To: [EMAIL PROTECTED]
> Subject: designing subnets with all ones/zeros.. [7:695]
>
> I have two questions regarding using the all ones and/or the all zeros
> subnet.
>
> Recently one of my co-workers started studying for CCNA and while
> reviewing subnets he kept telling me that you could not use the all zero
> or all ones subnet.
>
> CL: classically speaking this is true. Early implementations, etc. these
> days this is no longer the case
>
> The Win95, NT, and LINUX hosts didn't have a
> problem with it nor did the routers.
>
> CL: a long time ago on this list we had a discussion of wacky subnet
masks.
> In the course of researching this, I found that the windows IP stack was
not
> rfc 1812 compliant in that it allowed discontiguous / wacky / non
contiguous
> ones subnet masks, and that windows also categorically denied use of
certain
> legitimate ip addresses. Such as 172.16.1.255/16 I believe that this is
> corrected in Win2K
>
> I tested it with RIP & EIGRP.
> (skipped OSPF since it is classful).
>
> CL: I believe you meant to say "classless" ;->
>
> I found that Cisco and others vendors agree that it will work, but they
> "Strongly discourage using the all ones or all zeros subnets"
>
> CL: where did you find language about "strongly discourage"?
>
> PS: if some of you try testing this; note that prior to 12.1 you'll need
> to enter
> (config)# ip zero-subnet
> before the router will accept a zero subnet on a interface. Starting in
> 12.1 the zero subnet is enabled by default.
>
> CL: ip subnet-zero
>
> Question #1: What type problems could you run into by using a all
> ones/zero subnet.
>
> CL: issues with older equipment / obsolete equipment / old OS versions
>
> Question #2: For you folks that are in design; Do you follow or
> ignore the "DO NOT USE ALL ONES/ZEROS" rule?
>
> CL: use both all the time. Of course I sell new Cisco equipment, so there
is
> no issue with most customers. Or I sell EIGRP or OSPF designs. Same thing.
> ;->
>
> I'm trying to get a real world idea of what the standard practice is.
> I work at a large corp, so I haven't a clue what sane people do.
>
> CL: so do I and neither do I.
>
> DaveC
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