192.168.10.0/24 - why /24 ? instead of 192.168.10/# notation query

[Scott]

Please note the query below is about a LABEL in an ALPHANUMERIC field which
could contain anything but its the example of a notation i dont understand.

1Im looking at a hardware firewall to understand the layout of the rules.
One of the destinations shows the address "name" field as: 192.168.10.0/24

("name" field is alpha numeric and is just a label).

When i EDIT the NAME that hold the rule for the address, the actual numeric
address is displayed as: 192.168.10.0/255.255.255.0

I understand subnet 255.255.255.0 allows 256 IPs.

So what im trying to get my head around is why "name" the destination
192.168.10.0/24 as when i actaully edit the addrees its actually
192.168.10.0/255.255.255.0.

I understand this means allowing packet traffic incoming to 192.168.10.#.

But why name it "192.168.10.0/24" ?

Why not name it "192.168.10.#"

I see this with several ISPs i use, they tend to add "IP/ number". Dont
understand the /number notation means. Can someone explain ?

Thank you.

[Chris M]

Scott wrote:
> <SNIP>
> But why name it "192.168.10.0/24" ?
>
> Why not name it "192.168.10.#"
>
> I see this with several ISPs i use, they tend to add "IP/ number". Dont
> understand the /number notation means. Can someone explain ?

The /24 is the number of 'on' bits in the subnet mask.

255.255.255.0, represented as octets in binary is:

11111111.11111111.11111111.00000000

Count the 1's :-)

--
Chris.

[JohnB]

It's called Slash Notation. And as Chris M said, it represents the number
of bits in the subnet mask.

Here's a link with further info:
http://www.rm.com/Support/TechnicalA...cref=TEC543024


"Scott" <nospam2211@yahoo.co.uk> wrote in message
news:%236m6V3rLJHA.2760@TK2MSFTNGP06.phx.gbl...
> Please note the query below is about a LABEL in an ALPHANUMERIC field
> which could contain anything but its the example of a notation i dont
> understand.
>
> 1Im looking at a hardware firewall to understand the layout of the rules.
> One of the destinations shows the address "name" field as: 192.168.10.0/24
>
> ("name" field is alpha numeric and is just a label).
>
> When i EDIT the NAME that hold the rule for the address, the actual
> numeric address is displayed as: 192.168.10.0/255.255.255.0
>
> I understand subnet 255.255.255.0 allows 256 IPs.
>
> So what im trying to get my head around is why "name" the destination
> 192.168.10.0/24 as when i actaully edit the addrees its actually
> 192.168.10.0/255.255.255.0.
>
> I understand this means allowing packet traffic incoming to 192.168.10.#.
>
> But why name it "192.168.10.0/24" ?
>
> Why not name it "192.168.10.#"
>
> I see this with several ISPs i use, they tend to add "IP/ number". Dont
> understand the /number notation means. Can someone explain ?
>
> Thank you.
>

[Scott]

> The /24 is the number of 'on' bits in the subnet mask.
>
> 255.255.255.0, represented as octets in binary is:
>
> 11111111.11111111.11111111.00000000
>
> Count the 1's :-)


Understood, simple now you mentiond it. So:

192.168.10.0 / 24

simply means:

192.168.10.# / on subnet 255.255.255.0 / meaning 256 IP available on the
subnet.

Its just another way to display 255.255.255.0 without writing it !

Thanks for the explaination guys :-)

[Scott]

thanks for the link too John.

[Chris M]

Scott wrote:
>> The /24 is the number of 'on' bits in the subnet mask.
>>
>> 255.255.255.0, represented as octets in binary is:
>>
>> 11111111.11111111.11111111.00000000
>>
>> Count the 1's :-)
>
>
> Understood, simple now you mentiond it. So:
>
> 192.168.10.0 / 24
>
> simply means:
>
> 192.168.10.# / on subnet 255.255.255.0 / meaning 256 IP available on the
> subnet.
>
> Its just another way to display 255.255.255.0 without writing it !
>
> Thanks for the explaination guys :-)

No probs. While we're talking about it, remember that there won't be 256
usable addresses:

192.168.10.0 is the network ID

192.168.10.255 is the subnet broadcast address

--
Chris.