Date: Sun, 11 Aug 2013 21:20:40 +0200 From: Damien Fleuriot <ml@my.gd> To: saeedeh motlagh <saeedeh.motlagh@gmail.com> Cc: Kimmo Paasiala <kpaasial@gmail.com>, s m <sam.gh1986@gmail.com>, Peter Wemm <peter@wemm.org>, FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: how calculate the number of ip addresses in a range? Message-ID: <ECCA98F7-EE1E-4EC1-AB7B-2F9270CBA3EF@my.gd> In-Reply-To: <CAN%2BS=WAZCx5mQ_AgO77UOyEhXKVHiDJ%2B=0vjTVW89OnbBBpDBA@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> <D07EECB0-2066-4187-8321-6D8F83089FD5@my.gd> <CAN%2BS=WAZCx5mQ_AgO77UOyEhXKVHiDJ%2B=0vjTVW89OnbBBpDBA@mail.gmail.com>
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Yup. Your available addresses are: (2 ^ (32 - netmask) ) - 2 Example for a 29: 2^3 - 2 Example for a /28: 2^4 - 2 On 11 Aug 2013, at 06:39, saeedeh motlagh <saeedeh.motlagh@gmail.com> wrote:= > thank you all guys for your answers. > Peter, of course it's not my homework!!!!!! in fact, i have a program whic= h manages dhcp. i want to limit the number of ip address which can be assign= ed by dhcp server. in order to do that, i should know how many ip addresses a= re available in the range that is defined for server and if the number of av= ailable ip addresses are greater than valid threshold, it's error. so as you= said, i should know the math for calculate this number. >=20 > thank you again guys for your answers but they do not solve my problem. an= y body knows what is the formula to calculate the valid ip addresses for any= desired ranges? > Thanks=20 >=20 >=20 > On Sat, Aug 10, 2013 at 5:19 AM, Damien Fleuriot <ml@my.gd> wrote: >>=20 >>=20 >> On 10 Aug 2013, at 01:07, Kimmo Paasiala <kpaasial@gmail.com> wrote: >>=20 >> > 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 rel= ated 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 r= ange? >> >>>>> for example if i have 192.0.0.1 192.100.255.254 with mask 8, how ma= ny ip >> >>>>> addresses are available in this range? is there any formula to calc= ulate >> >>>>> 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 / assignme= nt? >> >>>> >> >>>> Anyway, you can think of it by converting your start and end address= es >> >>>> to an integer. Over simplified: >> >>>> >> >>>> $ 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 >> >>>> >> >>>> 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 >>=20 >>=20 >> Kimmo, >>=20 >> That is untrue regarding /31 netmasks where you theoretically have 2^1 -2= addresses. >>=20 >> With such a short netmask the only 2 addresses are usable. >> _______________________________________________ >> freebsd-net@freebsd.org mailing list >> http://lists.freebsd.org/mailman/listinfo/freebsd-net >> To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" >=20 >=20 >=20 > --=20 > Sa.M
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