Mailinglist Archive: opensuse (3378 mails)

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RE: [SLE] Subnet mask settings....
  • From: "John W Higgins" <john@xxxxxxxxxxx>
  • Date: Fri, 12 Apr 2002 09:12:11 -0700
  • Message-id: <BBEHLJJGKJFFHNBNPOEGMEOPFGAA.john@xxxxxxxxxxx>
Hi Michael,

Actually the short answer to your question is that you leave the subnet mask
as 255.255.255.0 - that subnet mask simply means that the first 24 bits are
the subnet and you have 8 bits (256 - 2 reserved (0 and 255)) of hosts per
subnet.

Ok, that doesn't look very good in terms of ease of understanding so lets
show some examples

10.a.b.c is your address.

Under 255.255.255.0 subnet you have 10.a.b as your subnet and c and your
address within the subnet.

That means that 10.0.0 is a subnet and 10.10.0 is another subnet under your
current netmask of 255.255.255.0 each with 254 hosts in the subnet. If you
have no requirement of more then 254 hosts in your subnet then you can just
leave 255.255.255.0 as your subnet mask and move onto much more interesting
things.

HOWEVER, if you require more then you need to change the subnet mask to
something like 255.255.0.0 on ALL your subnets including the current 10.0
subnet. That's because under 255.255.0.0 you have 16 bits of subnet and 16
bits of hosts - this would give you the range of 10.a for your subnets from
the above example and about 65000 or so hosts under each subnet (the b.c
portion of the above example).

The subnet mask does not change based on which subnet you are in - the
subnet mask is an architectural choice you make when laying out your network
from the beginning. So if 254 hosts works then 255.255.255.0 gives you about
65000 subnets, otherwise I would suggest 255.255.0.0 for 65000+ hosts per
subnet with 256 subnets available. There are points in between but unless
you really need something more precise - nice clean subnet masks with 255 in
them make your life a WHOLE lot easier.

John W Higgins
john@xxxxxxxxxxx

-----Original Message-----
From: Michael Garabedian [mailto:mikejr@xxxxxxxxxxxxxxx]
Sent: Friday, April 12, 2002 7:46 AM
To: suse-linux-e@xxxxxxxx
Subject: RE: [SLE] Subnet mask settings....



Isn't there some rule that goes up by a certain amount.
Like 10.0.0.0/8 is something
And 10.0.0.0/128 is something...is there a table I can find these things
out with or what is the math on this.
-----Original Message-----
From: Pep Serrano [mailto:pep@xxxxxxxxxxx]
Sent: Friday, April 12, 2002 9:55 AM
To: suse-linux-e@xxxxxxxx
Subject: Re: [SLE] Subnet mask settings....


Hello Michael

If you just want to have a second network why do you want to change the
mask?
I just don't know why you want to set mask 255.254.255.0 for your
private
network.

Do you have enough with a 255.255.255.0 that gives you 255 client ips
(10.10.0.1 to 10.10.0.254) ?

In case you need more addresses then you may change your mask.

> The second network I want to make 10.10.0.0
> What would the subnet mask be. 255.254.255.0

Pep Serrano

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