Question about subnetting /24's

Scott Gifford sgifford at
Fri Mar 19 01:42:31 UTC 1999

OK, so this is probably somewhat of a stupid question.  But I thought
I knew this stuff, and so did the tech support guy I almost ended up
in a screaming match with.  :)  Can anybody let me know if I'm missing
something I should know by now?

I have a /24 network I want to subnet into two /25's.  For realism's
sake, let's call the network   (mask

So I have two 126-host networks, namely   (mask (mask

The person with whom I was calmly discussing the matter said that this
configuration didn't make any sense, because my first subnet had all
zeroes in the last octet, so it was an all-zeroes subnet; and the
second had all ones on the last octet, so it was an all-ones subnet.
And that these subnets were reserved as the network subnet, and the
broadcast subnet, much as all-zeroes and all-ones in the host portion
indicate the network and broadcast addresses.

I would have dismissed this out of hand, but our router wouldn't let
us use this first network unless I enabled the "zero subnet enable"
option.  And with the second, the customer had to say it was an
all-ones subnet or some such thing.  This seemed to imply that maybe I
was doing something weird.

Both myself and the customer are using Bay Networks routers.

Can anybody shed any light on this?  Is this just something I've
competely missed in everything I've learned about IP?  Are my routers
crazy?  Is the tech support guy crazy?  Is it just that I've finally
gone crazy?...

  Oh, and while I'm on the subject, is there a cleaner way to delegate
IN-ADDR.ARPA for subnets of a /24 than 128 seperate delegations, one
for each individual IP address we've assigned?

  If anybody else is interested in this, let me know, and I'll
summarize direct responses to the list.

Thanks for any insight, suggestions, ideas, or referrals to a good
psychiatrist in the Greater Flint area,


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