| Author |
Subneting question
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| cm2gj 2002-02-09, 11:58 pm |
| 1- What ip adress class is required to provide 2000 ip addresses???.
2- How many ip adress will be provided and how many will be unused?? | |
| unreal 2002-02-10, 3:18 am |
| It will be a Classless Inter-Domain Routing network type.
Or the so call slash 21 network, provided by the ISP or the IANA.
Class C is inadequate while class B is overkills unless you don't mind paying that much.
It means you will be given the lower 11 bit, which will have 2 to the power of 11 = 2048 hosts.
Okay, we can't use all the 2048 hosts- in binary looks like this :
XXXXXXXX XXXXXXXX XXXXX111 11111111- which is reserved for broadcasts.
x represent the bits controlled by the IANA.
Similarly, we can't use the network Id, which looks like:
xxxxxxxx xxxxxxxx xxxxx000 00000000
And usually, each subnet needs a router Ip address.
Therefore you have actually 2048-3= 2045 usable ip addresses.
hope that helps. | |
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| cm2gj 2002-02-10, 12:26 pm |
| I agree with you but i have a doubt...
its a CIDR of course, with /21 as network ID / 11 bytes left for host ID....
as a formula say 2^11= 2048 - 2 = 2044
2044 hosts...
44 unusable hosts....
why you rest 3 instead of 2?????? | |
| unreal 2002-02-10, 7:16 pm |
| quote:
Originally posted by cm2gj
I agree with you but i have a doubt...
its a CIDR of course, with /21 as network ID / 11 bytes left for host ID....
as a formula say 2^11= 2048 - 2 = 2044
2044 hosts...
44 unusable hosts....
why you rest 3 instead of 2??????
The one is reserve for router or the so call default route address.
Each subnet has at least one router;after all if it didn't have a router, then the subnet could'nt talk to any other networks, and it wouldn't be an intranet.
By convention, the first address after the network number is the default gateway(router) address.
Yes, I won't say 2 is not correct, as the default route is incidentally, also a usable IP, but usually it is reserve. | |
| chodan 2002-02-10, 7:31 pm |
| THose extra hosts
whould be good for router interfaces
Seeing as you won`t have all that address space on one flat network.
Cisco advises no more than 500 hosts in a broadcast domain, I`m not sure what Microsoft advises.
I personaly wouldn`t put more than 200 on a broadcast domain.
So I would use the extra 44 "not sure about your math there" for router interfaces.
QUOTE {{as a formula say 2^11= 2048 - 2 = 2044}}
Doesn`t 2048 - 2 = 2046 ?
the - 2 is for the broadcast and network addresses did you take out 2 more for some nefarious purpose? :-) | |
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| I know a ISP that asign 254 instead of 1 to routers!!!!
additonally.... When in M$ questions say how many host you can use in .... etc... you only need to rest 2, not 3....... donīt matter if you have a router or a horse....
thanks for your posts!! | |
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| 2048-2 = 2046............ 2 less as you know... evidentely is a mistyped error....
thanks!! | |
| chodan 2002-02-10, 8:36 pm |
| Where I work we have a 7 class C`s
we have one of those blocked off with a /30
subnet mask and we use that for our router interfaces.
say we have 2 router interfaces connected together the /30 gives us an address for each interface.
Although to some it might seem we are wasting half of a class C it does make
documentation of our routers easier. | |
| unreal 2002-02-11, 12:10 am |
| Chodan has given us some insight, that we would otherwise not find in a book. It beens educational. | |
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| Chodan... please explain me something:
iīm new in subneting... i donīt have any experience and about two days i understand something thanks to the subneting guide of mcsefreaks.com
you say that you use a /30 subnet.
a /x subnet is a CIDR subnet no?
30 bits in a subnet only left 2 bits for hosts id...
using the formula (2^N)-2 then we have only 2 available hosts for this subnet /30.... why you make this?????
its my analisis wrong??? | |
| wirechild 2002-02-16, 11:39 pm |
| cm2gj
you would use a /30 for a connection between 2 routers (such as in a PPP connection with your router and the router at your ISP). This put's these interfaces on their own net. This is probably one of the only reasons to use such a small net but I have used /30 and /29 for many of other reasons 
By the way, you should never ever assume the scenario that unreal gave as being the way to go. Yes in some cases you will use one of the IP's for your router but this is still a valid or usable IP for hosts. You can assign 2046 IP's to your hosts in this example. Only the Wire and Broadcast cannot be assigned to hosts.
A ROUTER is a host also!!!!!!!!!!!!!!
Rick | |
| cm2gj 2002-02-16, 11:55 pm |
| [QUOTE]Originally posted by wirechild
[B]cm2gj
i know that the router / printer with NIC interface / etc are considered Hosts.. of course... but i have some concepts lost in subneting.... some times i see some questions that make me crazy!!!! | |
| wirechild 2002-02-17, 12:04 am |
| I when I first tried to grasp some of the more difficult subneting I found this site very helpful:
http://www.certnotes.com/microsoft/...ySubnetting.htm
Look through what he has and then check out the second page that is linked at the bottom.
I then created many examples on my own and figured them out. Such as, 50 Networks and 400 host/net with a /19 from my provider and so on. Some of the samples I dreamed up wasn't possible and this was the best ones as it really helped me to understand these types of scenarios you origianlly wrote about! | |
| cm2gj 2002-02-17, 12:47 am |
| Thanks too much for your help and your time. Its a very good link.. iīm see it now... |
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