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-----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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