x.x.x.x/N notation question

I do not understand x.x.x.x/N notation.

Could someone reply with a url or discription of how it works.
Browsing through network HowTos has not helped.

I am trying to use it in my firewall rules to block some networks.

I thought it was number of bits but that did not pan out when looking
at the following

124.0.0.0/7
126.0.0.0/8
169.208.0.0/12
196.192.0.0/13

"Bit Twister" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...

> I do not understand x.x.x.x/N notation.
> Could someone reply with a url or discription of how it works.

I find http://bob.marlboro.edu/~msie/2003/i...ep14/ipcalc.pl to be
most helpful.

> I thought it was number of bits but that did not pan out when looking
> at the following
> 124.0.0.0/7

e.g.:
Address: 124.0.0.0 0111110 0.00000000.00000000.00000000
Netmask: 254.0.0.0 = 7 1111111 0.00000000.00000000.00000000
Wildcard: 1.255.255.255 0000000 1.11111111.11111111.11111111
=>
Network: 124.0.0.0/7 0111110 0.00000000.00000000.00000000 (Class A)
Broadcast: 125.255.255.255 0111110 1.11111111.11111111.11111111
HostMin: 124.0.0.1 0111110 0.00000000.00000000.00000001
HostMax: 125.255.255.254 0111110 1.11111111.11111111.11111110
Hosts/Net: 33554430

Hi -

On Tue, 20 Dec 2005 23:29:31 -0600, Bit Twister
<(E-Mail Removed)> wrote:

>I do not understand x.x.x.x/N notation.
>
>Could someone reply with a url or discription of how it works.
>Browsing through network HowTos has not helped.
>
>I am trying to use it in my firewall rules to block some networks.
>
>I thought it was number of bits but that did not pan out when looking
>at the following

N is the number of bits, starting from the left, that don't change. It
defines a range where the bits following the first N bits range from
all zeros to all ones.

>124.0.0.0/7

124.0.0.0 as bits = 01111100 00000000 00000000 00000000
First seven bits = ^^^^^^^
7 fixed, rest 0s = 01111100 00000000 00000000 00000000
7 fixed, rest 1s = 01111101 11111111 11111111 11111111

01111100 00000000 00000000 00000000 = 124.0.0.0
01111101 11111111 11111111 11111111 = 125.255.255.255

So 124.0.0.0/7 defines the range of 124.0.0.0 to 125.255.255.255.

125.255.255.255/7 also defines that same range as does any IP address
in that range with /7, but it is traditional (and easier to follow)
when all bits after the first N bits are zero. And some software
insists on it being that way.

Since there are 32 bits in an IPv4 IP address, N must be 0 to 32.
/0 defines the entire range of IPv4 IP addresses.
/32 defines a single IP address.

--
Ken
http://www.ke9nr.net/

On Tue, 20 Dec 2005 21:48:46 -0800, ynotssor wrote:
> "Bit Twister" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
>
>> I do not understand x.x.x.x/N notation.
>> Could someone reply with a url or discription of how it works.
>
> I find http://bob.marlboro.edu/~msie/2003/i...ep14/ipcalc.pl to be
> most helpful.

Hmmm, Bob needs to fix his example.
Using the example in the code, I get

$ ipcalc.pl 230.143.254.1/25
/home/bittwister/work/ipcalc.pl: error: First byte must be 1-223,
I do not handle multicast or experimental
usage: /home/bittwister/work/ipcalc.pl IPv4_address[/mask]
mask can be number of bits (0-32) or dotted quad

To me my first byte is 2, now had he indicated
first quad (230) must be 1-223 it would have helped.


>> I thought it was number of bits but that did not pan out when looking
>> at the following
>> 124.0.0.0/7
>
> e.g.:
> Address: 124.0.0.0 0111110 0.00000000.00000000.00000000
> Netmask: 254.0.0.0 = 7 1111111 0.00000000.00000000.00000000
> Wildcard: 1.255.255.255 0000000 1.11111111.11111111.11111111
> =>
> Network: 124.0.0.0/7 0111110 0.00000000.00000000.00000000 (Class A)
> Broadcast: 125.255.255.255 0111110 1.11111111.11111111.11111111
> HostMin: 124.0.0.1 0111110 0.00000000.00000000.00000001
> HostMax: 125.255.255.254 0111110 1.11111111.11111111.11111110
> Hosts/Net: 33554430

So it is the number of bits, my fault for counting from the right
instead of the left. That is what I get for reading about Netmask and
thinking the 0s were the wildcard mask to get the actual ip addy.

Also does not help being a hardware tech knowing about and, nand, or,
xor logic and software numbering bits starting on the right.

Thank you.

"Bit Twister" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...

> > I find http://bob.marlboro.edu/~msie/2003/i...ep14/ipcalc.pl to
be
> > most helpful.
>
> Hmmm, Bob needs to fix his example.
> Using the example in the code, I get
>
> $ ipcalc.pl 230.143.254.1/25
> /home/bittwister/work/ipcalc.pl: error: First byte must be 1-223,
> I do not handle multicast or experimental
> usage: /home/bittwister/work/ipcalc.pl IPv4_address[/mask]
> mask can be number of bits (0-32) or dotted quad
>
> To me my first byte is 2, now had he indicated
> first quad (230) must be 1-223 it would have helped.

Hmmm, I must have a different version:
$ ./ipcalc.pl 230.143.254.1/25
Address: 230.143.254.1 11100110.10001111.11111110.0 0000001
Netmask: 255.255.255.128 = 25 11111111.11111111.11111111.1 0000000
Wildcard: 0.0.0.127 00000000.00000000.00000000.0 1111111
=>
Network: 230.143.254.0/25 11100110.10001111.11111110.0 0000000 (Class D)
Broadcast: 230.143.254.127 11100110.10001111.11111110.0 1111111
HostMin: 230.143.254.1 11100110.10001111.11111110.0 0000001
HostMax: 230.143.254.126 11100110.10001111.11111110.0 1111110
Hosts/Net: 126

> So it is the number of bits, my fault for counting from the right
> instead of the left.

I thought that that might have been the case, but a picture is worth a
thousand words, as they say.

> Thank you.

You're welcome.

On Wed, 21 Dec 2005 01:23:17 -0800, ynotssor wrote:
>
>I find http://bob.marlboro.edu/~msie/2003/i...ep14/ipcalc.pl to
>
> Hmmm, I must have a different version:
> $ ./ipcalc.pl 230.143.254.1/25

I'll guess so, I used the supplied link and

$ type ipcalc.pl
ipcalc.pl is hashed (/home/bittwister/work/ipcalc.pl)

indicates that is the one I donwloaded and is the one which runs.

On Tue, 20 Dec 2005 23:29:31 -0600, Bit Twister shouted Hoy......

>
>
> I do not understand x.x.x.x/N notation.
>
> Could someone reply with a url or discription of how it works.
> Browsing through network HowTos has not helped.
>
> I am trying to use it in my firewall rules to block some networks.
>
> I thought it was number of bits but that did not pan out when looking
> at the following
>
> 124.0.0.0/7
> 126.0.0.0/8
> 169.208.0.0/12
> 196.192.0.0/13

It is cidr

Have a look at:

http://learnlinux.tsf.org.za/courses...n/ch01s12.html

--
Dancin' in the ruins tonight
mail: echo onub-(E-Mail Removed) | perl -pe 'y/a-z/n-za-m/'
Tayo'y Mga Pinoy

On Tue, 20 Dec 2005, in the Usenet newsgroup comp.os.linux.networking,
in article <(E-Mail Removed)>, ynotssor wrote:

>"Bit Twister" <(E-Mail Removed)> wrote

>> I do not understand x.x.x.x/N notation.
>> Could someone reply with a url or discription of how it works.
>
>I find http://bob.marlboro.edu/~msie/2003/i...ep14/ipcalc.pl to be
>most helpful.

1878 Variable Length Subnet Table For IPv4. T. Pummill, B. Manning.
December 1995. (Format: TXT=19414 bytes) (Obsoletes RFC1860) (Status:
INFORMATIONAL)

It also includes references to the CIDR documents that caused all of this.
RFC1878 is available at many sites on the web.

Old guy