EIGRP has no class either... :)
David Chandler wrote:
> 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
> > FAQ, list archives, and subscription info:
> > http://www.groupstudy.com/list/cisco.html
> > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
> FAQ, list archives, and subscription info:
http://www.groupstudy.com/list/cisco.html
> Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
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