IamGimli
join:2004-02-28
Canada
 ·Primus Talkbroadband
 ·B2B2C High-Speed I..
| reply to verifone411
Re: How do I determine subnet manually?
Since you asked, here's the "how".
A subnet mask determines how many bits of your IP address are static for a particular subnet.
Let's use your class B as an example. 141.67.0.0 is represented as 10001101.01000011.00000000.0000000 in binary. The subnet mask of your class B is /16, because the first 16 bits of that address will never change. When you want to further separate that class B in smaller subnet you remove more bits that will not change for that subnet.
For example, koitsu's suggestion of /20 subnets to get the most subnets out of your class B while having at least 4000 addresses in each subnet makes your first subnet 10001101.01000011.0000xxxx.xxxxxxxx in binary. That means that subnet includes every addresses between 10001101.01000011.00000000.00000000 and 10001101.01000011.00001111.11111111 (141.67.0.0 to 141.67.15.255). Your second subnet would be 10001101.01000011.0001xxxx.xxxxxxxx (141.67.16.0 to 141.67.31.255), your third 10001101.01000011.0010xxxx.xxxxxxxx (141.67.32.0 to 141.67.47.255), etc.
The x represent every variable bit in the addresses for that subnet.
If you went with a /22 subnet mask instead, the mask would look like 10001101.01000011.000000xx.xxxxxxxx and the addressable range in your first subnet would be 10001101.01000011.00000000.00000000 to 10001101.01000011.00000011.11111111 (141.67.0.0 to 141.67.3.255). |
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Bobthebuilder
@instantnetworks.net | 141.67.0.0 is represented as 10001101.01000011.00000000.0000000
How do you convert to binary without a calculator that I see all over the net? |
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IamGimli
join:2004-02-28
Canada
·Primus Talkbroadband
·B2B2C High-Speed I..
edit:
May 8th, @01:54PM
| In binary, each position is an exponent of 2 (instead of an exponent of 10 in the decimal system). The first position is therefore worth 1 (2^0), the second position is worth 2 (2^1), the third 4 (2^2), etc. From that it's a bit of mental work to determine the whole number. For 141, for example, what whole exponents of 2 are represented? You got 128 (2^8) or 10000000 in binary, plus 8 (2^4) or 1000, plus 4 (2^3) or 100, plus 1 (2^0) or 1.
bin 10000000 + 1000 + 100 + 1 = 10001101
dec 128 + 8 + 4 + 1 = 141
hex 80 + 8 + 4 + 1 = 8D (disregard that, I'm just trying to confuse you with hexadecimal i.e. base 16 now  )
BTW even the Windows calculator can easily translate from decimal to binary values. Just switch it to scientific mode and you'll see the Hex, Dec, Oct and Bin radio button on the left side. Enter a number while the radio button is on Dec, click on the Bin button and see it represented in binary. Just remember to add the leading zero(s) if your value is less than 128 and you are representing an IP address. Each of the four bytes in the IP address needs to be represented by 8 binary positions or bits (hence why you represent 67 with 01000011 instead of just 1000011). |
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verifone411
join:2008-05-08
| Thanks for the infomation. Sticking with the first class b number (does that change things since you decided to move the example to a class c?)
How do you know and how do you determine that...
/24 = 256 IPs = 254 Usable ? i know the diagrams say that.
Is it because the last 2 sets of octects represent 8 bits each for a total of 16. Each 16 bit placeholder can have 2 different values so that is why you raise it to the power of 2? to get 65536- 2=65534 usable? |
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tschmidt
Premium,MVM
join:2000-11-12
Milford, NH
·Verizon Online DSL
| Each octet is 8-bits. A /24 address means 24-bits of address are reserved for network leaving 8 for host. This assumes you are talking about IPv4 with a 32-bit address range.
An Octet is FFh or 256 (in decimal notion) However, since the lowest address is reserved as network address and highest for broadcast that leaves 254 available host addresses.
Dotted Decimal was a convenient way to represent IP address when Class-full addressing was used since Class boundaries were also octet boundaries. With the advent of classless routing where split between network and host address can occur anywhere dotted decimal is a little like using Roman numerals to build a house.
If you stick with binary or hex it is a lot less confusing.
/tom |
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IamGimli
join:2004-02-28
Canada
·Primus Talkbroadband
·B2B2C High-Speed I..
| said by tschmidt  :If you stick with binary or hex it is a lot less confusing. I understand binary but how is hexadecimal any less confusing than decimal to represent network addresses? It may make them a bit shorter to write but I don't see any difference in the confusion aspect. |
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tschmidt
Premium,MVM
join:2000-11-12
Milford, NH
·Verizon Online DSL
| said by IamGimli :I understand binary but how is hexadecimal any less confusing than decimal to represent network addresses? It may make them a bit shorter to write but I don't see any difference in the confusion aspect. Dotted decimal represents a discontinuous counting method. If I add 1 to FFh I get 100h. If I add 1 to 0.255 (dotted decimal) I get 1.0. Life gets even more exciting if I start playing with masking lower order bits.
If I want to mask the 2 low order bits I have
1111 1100 b (binary)
FCh (hex)
252 Decimal
Perhaps I'm unique (after all this is not my day job) but I find it impossible to do arithmetic in dotted decimal.
/tom |
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