Question about subnetting /24's

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. :slight_smile: 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

  216.40.155.0/24 (mask 255.255.255.0)

So I have two 126-host networks, namely

  216.40.155.0/25 (mask 255.255.255.128)
  216.40.155.128/25 (mask 255.255.255.128)

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,

------Scott.

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

Please don't. This list isn't for primary school IP networking homework
questions.

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

You should try the Psychiatrists Referral Service
   15920 W 12 Mile Rd
   Southfield, MI 48076
   (248) 552-8753

P.S. You might want to refer to some RFCs as well
http://www.faqs.org/rfcs/rfc2072.html
http://www.faqs.org/rfcs/rfc1812.html

P.P.S. You're probably right but if you can't make the customer's
equipment work and you can't back up your claims with reference to a
higher authority, then you gotta be crazy.

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

216.40.155.0/24 (mask 255.255.255.0)

So I have two 126-host networks, namely

216.40.155.0/25 (mask 255.255.255.128)
216.40.155.128/25 (mask 255.255.255.128)

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.

He is correct for "classful" networking. If you run classless IP, his
comments are irrelevant.

Both myself and the customer are using Bay Networks routers.

Ahhhhhh. I see your problem. :stuck_out_tongue:

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

I'm afraid that most people here know better. But thanx anyway.

------Scott.

TTFN,
patrick

I Am Not An Isp - www.ianai.net
ISPF, The Forum for ISPs by ISPs, <http://www.ispf.com>
"Think of it as evolution in action." - Niven & Pournelle

Since I'm up I might as well reply...

In the preCIDR world (as I recall) the use of the all zeros and all ones
subnet was frowned on. When VLSM and CIDR became the norm this sorta
stopped. It was more a fact that it is the largest waste of IPs known.
However saying that many (including CISCO) still have config rules
stopping it by default. So in other words ya need to turn the knob.
Don't use Bay but you would think the support folks would clearly know
about this.... then again....

Chris MacFarlane
Manager, Network Operations
ACC Telenterprises

This list isn't for primary school IP networking homework questions.

this radical change will be much appreciated

randy