Date: Sat, 10 Aug 2013 02:50:53 +0200 From: Damien Fleuriot <ml@my.gd> To: Kimmo Paasiala <kpaasial@gmail.com> Cc: FreeBSD Net <freebsd-net@freebsd.org>, s m <sam.gh1986@gmail.com>, Peter Wemm <peter@wemm.org> Subject: Re: how calculate the number of ip addresses in a range? Message-ID: <D26861AC-EF63-4842-931F-9BFD55127C81@my.gd> In-Reply-To: <CA%2B7WWScKd2nYD7GA1Wxqr%2BAF2Qzsyoi89gvD51mgNNcH8v6wAA@mail.gmail.com> References: <CAA_1SgEEeyCOk%2Bi9Zp725RfQ9s0tpELXL0SSBeiN%2B60z%2BxqYUg@mail.gmail.com> <CAGE5yCoBYS2%2BsHoQXZvWMNPTQeEEtDX7LAKSBHJAZ4_rA2-byQ@mail.gmail.com> <8B53C542-5CC3-45E6-AA62-B9F52A735EE5@my.gd> <CAGE5yCqURzYF2TYez6S6y=x4rWtKdL%2B-3zjGsDuz2LqGb18-RQ@mail.gmail.com> <CA%2B7WWSf_i7b66xSFP3Gk20Cq7v0mX_ynQg61GM9u1_0vZF5-wQ@mail.gmail.com> <CA%2B7WWScKd2nYD7GA1Wxqr%2BAF2Qzsyoi89gvD51mgNNcH8v6wAA@mail.gmail.com>
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On 10 Aug 2013, at 01:13, Kimmo Paasiala <kpaasial@gmail.com> wrote:
> On Sat, Aug 10, 2013 at 2:07 AM, Kimmo Paasiala <kpaasial@gmail.com> wrote:
>> On Sat, Aug 10, 2013 at 1:44 AM, Peter Wemm <peter@wemm.org> wrote:
>>> On Fri, Aug 9, 2013 at 9:34 AM, Fleuriot Damien <ml@my.gd> wrote:
>>>>
>>>> On Aug 8, 2013, at 10:27 AM, Peter Wemm <peter@wemm.org> wrote:
>>>>
>>>>> On Thu, Aug 8, 2013 at 12:04 AM, s m <sam.gh1986@gmail.com> wrote:
>>>>>> hello guys,
>>>>>>
>>>>>> i have a question about ip addresses. i know my question is not related to
>>>>>> freebsd but i googled a lot and found nothing useful and don't know where i
>>>>>> should ask my question.
>>>>>>
>>>>>> i want to know how can i calculate the number of ip addresses in a range?
>>>>>> for example if i have 192.0.0.1 192.100.255.254 with mask 8, how many ip
>>>>>> addresses are available in this range? is there any formula to calculate
>>>>>> the number of ip addresses for any range?
>>>>>>
>>>>>> i'm confusing about it. please help me to clear my mind.
>>>>>> thanks in advance,
>>>>>
>>>>> My immediate reaction is.. is this a homework / classwork / assignment?
>>>>>
>>>>> Anyway, you can think of it by converting your start and end addresses
>>>>> to an integer. Over simplified:
>>>>>
>>>>> $ cat homework.c
>>>>> main()
>>>>> {
>>>>> int start = (192 << 24) | (0 << 16) | (0 << 8) | 1;
>>>>> int end = (192 << 24) | (100 << 16) | (255 << 8) | 254;
>>>>> printf("start %d end %d range %d\n", start, end, (end - start) + 1);
>>>>> }
>>>>> $ ./homework
>>>>> start -1073741823 end -1067122690 range 6619134
>>>>>
>>>>> The +1 is correcting for base zero. 192.0.0.1 - 192.0.0.2 is two
>>>>> usable addresses.
>>>>>
>>>>> I'm not sure what you want to do with the mask of 8.
>>>>>
>>>>> You can also do it with ntohl(inet_addr("address")) as well and a
>>>>> multitude of other ways.
>>>>
>>>>
>>>> Hold on a second, why would you correct the base zero ?
>>>> It can be a valid IP address.
>>>
>>> There is one usable address in a range of 10.0.0.1 - 10.0.0.1.
>>> Converting to an integer and subtracting would be zero. Hence +1.
>>>
>>> --
>>
>> To elaborate on this, for every subnet regardless of the address/mask
>> combination there are two unusable addresses: The first address aka
>> the "network address" and the last address aka the "broadcast
>> address". There may be usable address in between the two that end in
>> one of more zeros but those addresses are still valid. Some operating
>> systems got this horribly wrong and marked any address ending with a
>> single zero as invalid, windows 2000 was one of them.
>>
>> -Kimmo
>
> Of course I should have mentioned that there are special cases to
> address/mask combinations, /31 and /32 masks have to be treated
> specially or there are no usable addresses at all.
>
> -Kimmo
Fully agree, /31 and /32 are special cases indeed.
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