Date: Sat, 10 Aug 2013 02:49:45 +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: <D07EECB0-2066-4187-8321-6D8F83089FD5@my.gd> In-Reply-To: <CA%2B7WWSf_i7b66xSFP3Gk20Cq7v0mX_ynQg61GM9u1_0vZF5-wQ@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>
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On 10 Aug 2013, at 01:07, 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:
>>>=20
>>> On Aug 8, 2013, at 10:27 AM, Peter Wemm <peter@wemm.org> wrote:
>>>=20
>>>> On Thu, Aug 8, 2013 at 12:04 AM, s m <sam.gh1986@gmail.com> wrote:
>>>>> hello guys,
>>>>>=20
>>>>> i have a question about ip addresses. i know my question is not relate=
d to
>>>>> freebsd but i googled a lot and found nothing useful and don't know wh=
ere i
>>>>> should ask my question.
>>>>>=20
>>>>> i want to know how can i calculate the number of ip addresses in a ran=
ge?
>>>>> for example if i have 192.0.0.1 192.100.255.254 with mask 8, how many i=
p
>>>>> addresses are available in this range? is there any formula to calcula=
te
>>>>> the number of ip addresses for any range?
>>>>>=20
>>>>> i'm confusing about it. please help me to clear my mind.
>>>>> thanks in advance,
>>>>=20
>>>> My immediate reaction is.. is this a homework / classwork / assignment?=
>>>>=20
>>>> Anyway, you can think of it by converting your start and end addresses
>>>> to an integer. Over simplified:
>>>>=20
>>>> $ cat homework.c
>>>> main()
>>>> {
>>>> int start =3D (192 << 24) | (0 << 16) | (0 << 8) | 1;
>>>> int end =3D (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
>>>>=20
>>>> The +1 is correcting for base zero. 192.0.0.1 - 192.0.0.2 is two
>>>> usable addresses.
>>>>=20
>>>> I'm not sure what you want to do with the mask of 8.
>>>>=20
>>>> You can also do it with ntohl(inet_addr("address")) as well and a
>>>> multitude of other ways.
>>>=20
>>>=20
>>> Hold on a second, why would you correct the base zero ?
>>> It can be a valid IP address.
>>=20
>> 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.
>>=20
>> --
>=20
> 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.
>=20
> -Kimmo
Kimmo,
That is untrue regarding /31 netmasks where you theoretically have 2^1 -2 ad=
dresses.
With such a short netmask the only 2 addresses are usable.=
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