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 IP Subnet Calculation & Design Online Documentation

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conrad

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Number of posts : 108
Age : 41
Location : Philippines
Registration date : 2008-09-27

PostSubject: IP Subnet Calculation & Design Online Documentation   Thu Nov 27, 2008 3:22 pm

IP Subnet Calculation & Design Online Documentation



Contents




Related Information



Purpose & Scope



The purpose of this tool is to provide a way to calculate IP
subnetting which is fast, easy, and error free.
Doing such calculations manually is time consuming and susceptible to
common mathematical mistakes (especially in conversions between binary
and decimal numbers).

While the tool is useful, it doesn't teach IP subnetting. It is
highly recommended that users understand the mechanics behind IP
subnetting by reading other sources like "Internetworking with TCP/IP"
by Comer.

This tool is for calculations only, and doesn't implement
limitations and rules imposed by various RFCs. For practical purposes,
users must understand these limitations and rules. For example, the
network 10.0.0.0 should not be advertised on internet and should be
used internally, however the tool doesn't distinguish this network
address from others.

User Interface



Inputs



IP Address is an input that specifies the IP address for which the subnet calculation and/or design is desired.


  • It can be a valid network, subnet or host address (class A, B, or C).
  • Ending zeros can be omitted, e.g. a network address 132.50.0.0 can be entered as 132.50 (or even 132.50.0).
  • Decimal numbers and dots typed in style of in IP address are the only valid characters.
  • This input is required for all actions.


Address Mask is an input that specifies the classful IP address mask using which the subnet calculation can be achieved.


  • It can be a valid mask or just the classful mask bits.
  • So, for a class B network address 132.50.0.0 a mask of
    255.255.255.0 or just 8 (bits of classful mask, not 24 bits which
    should be for classless mask) can be used.
  • Also ending zeros can be omitted, e.g. an address mask 255.255.255.0 can be entered as 255.255.255 only.
  • Decimal numbers and dots typed in style of in IP address mask are the only valid characters.
  • This input is required for actions "Calculate All IP Subnets" and "Find IP Subnet for this address".


Minimum Subnets is an input that specifies the minimum number of subnets that must be available in the subnet design.


  • It can be a any decimal number greater than zero.
  • This input is required for actions "Design IP Subnetting
    (maximize subnets)", "Design IP Subnetting (maximize hosts)", and
    "Design IP Subnetting (minimize wastage)".


Minimum Hosts/Subnet is an input that specifies the minimum number of hosts that must be available in every subnet of the subnet design.


  • It can be a any decimal number greater than zero.
  • This input is required for actions "Design IP Subnetting
    (maximize subnets)", "Design IP Subnetting (maximize hosts)", and
    "Design IP Subnetting (minimize wastage)".


VLSM Masks are inputs that specify the classful IP address
masks for calculation of subnetting which incorporates variable length
subnet masking (VLSM).


  • These can be valid masks or just the classful mask bits.
  • So, for a network address 132.50.0.0 a mask of 255.255.255.0
    or just 8 (bits of classful mask, not 24 bits which should be for
    classless mask) can be used.
  • Also ending zeros can be omitted, e.g. an address mask 255.255.255.0 can be entered as 255.255.255 only.
  • Decimal numbers and dots typed in style of in IP address mask are the only valid characters.
  • At least one of these inputs is required for action "Calculate
    Subnetting using VLSM". Others not specified will be taken as zero.


Actions



Calculate All IP Subnets


  • This action extracts network address and class from the IP Address (which can be network, subnet or host address).
  • Then it calculates all possible subnets using the given Address Mask or classful mask bits.


Find IP Subnet for this address




  • This action extracts host address from the given IP Address (which can be network, subnet, or host address).
  • Then it calculates the subnet address that contains this host address using the given Address Mask or classful mask bits.


Design IP Subnetting (maximize subnets)




  • This action extracts network address and class from the IP Address (which can be network, subnet or host address).
  • Then it calculates the classful mask bits from Minimum Subnets
    and Minimum Hosts/Subnets such that maximum subnets are available while
    minimum hosts/subnet requirement is met.
  • Finally, it calculates all possible subnets using the classful mask bits.


Design IP Subnetting (maximize hosts)


  • This action extracts network address and class from the IP Address (which can be network, subnet or host address).
  • Then it calculates the classful mask bits from Minimum Subnets
    and Minimum Hosts/Subnets such that maximum hosts/subnet are available
    while minimum subnets requirement is met.
  • Finally, it calculates all possible subnets using the classful mask bits.


Design IP Subnetting (minimize wastage)




  • This action extracts network address and class from the IP Address (which can be network, subnet or host address).
  • Then it calculates the classful mask bits from Minimum Subnets
    and Minimum Hosts/Subnets such that address space wastage is minimum
    while minimum subnets and minimum hosts/subnet requirements are met.
  • Finally, it calculates all possible subnets using the classful mask bits.


Calculate Subnetting using VLSM




  • This action extracts network address and class from the IP Address (which can be network, subnet or host address).
  • Then it sorts given VLSM Masks or classful mask bits in order of decreasing hosts/subnet.
  • Finally, it calculates all possible subnets, sub-subnets, and sub-sub-subnets using the given VLSM Masks or classful mask bits.
  • Note that this calculation applies to VLSM of class A, B, and
    C IP addresses only and is not meant for IP Classless calculations.


Interpreting Results



Sample Output 1



Source: This output is obtained by using IP Address
150.150.10.10, Address Mask 255.255.224.0 (or 3 classful mask bits),
and action "Calculate All IP Subnets".
The action "Find IP Subnet for this address" will give the same output
except that only one subnet will be shown which contains this IP
Address (subnet 0 in this case).

Action "Design IP Subnetting (maximize subnets)" will give exactly
the same output if Minimum Subnets between 1 and 6, and Minimum
Hosts/Subnet between 4096 and 8192 is used.
Action "Design IP Subnetting (maximize hosts)" will give exactly the
same output if Minimum Subnets between 4 and 6, and Minimum
Hosts/Subnet between 1 and 8192 is used.
Action "Design IP Subnetting (minimize wastage)" will give exactly the
same output if Minimum Subnets between 1 and 6, and Minimum
Hosts/Subnet between 4096 and 8192 is used.

-----------------------------------------------------------------------------
IP Class: B IP Address: 150.150.10.10
Mask Bits: 3 Subnet Mask: 255.255.224.0
Subnets: 6+1 IP Major Net: 150.150.0.0
Hosts/Subnet: 8190 Major Net Bcast: 150.150.255.255

Subnets for Fixed Length Subnet Masking
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
No. Subnet Hosts Hosts Broadcast
Address From To Address

0 150.150.0.0 150.150.0.1 150.150.31.254 150.150.31.255
1 150.150.32.0 150.150.32.1 150.150.63.254 150.150.63.255
2 150.150.64.0 150.150.64.1 150.150.95.254 150.150.95.255
3 150.150.96.0 150.150.96.1 150.150.127.254 150.150.127.255
4 150.150.128.0 150.150.128.1 150.150.159.254 150.150.159.255
5 150.150.160.0 150.150.160.1 150.150.191.254 150.150.191.255
6 150.150.192.0 150.150.192.1 150.150.223.254 150.150.223.255
7 150.150.224.0 150.150.224.1 150.150.255.254 150.150.255.255

Don't use subnet 0 (unless using ip subnet-zero command) and subnet 7.
Address space wasted by subnetting = 25.02% ( 12.52% with ip subnet-zero)
-----------------------------------------------------------------------------


Understanding: Top four lines show the basic information
like the
IP address and subnet mask (or mask bits) given by user, the extracted
IP class, network address (Major Net), and network broadcast address.
Also given are number of subnets [ = 2^(mask bits) -2 ] and
hosts/subnet [ = 2^(32 -16 -mask bits) -2 for class B]. The +1 in front
of subnets should be added if ip subnet-zero command is used on Cisco
router.

The table that follows shows info about each subnet including subnet
number, subnet address, first host address in subnet, last host address
in subnet, and subnet's broadcast address.

Note that even though all subnets are shown, subnet zero should not
be used as its subnet address matches the major net address (some older
versions of Unix also used an all zero broadcast which is another
factor in the problem). However, this restriction is waived if ip
subnet-zero command is used. Also the last subnet (7 in this case)
shouldn't be used as its broadcast address is the same as major net
broadcast address.

Finally, address space wastage is given. Address space is wasted
because subnet zero and the last subnet can't be used, and also because
the first address and the last address of the subnet can't be used
(first address identifies the subnet itself, and last address is its
broadcast address). This is also the reason for -2 in the above two
formulae. However, using ip subnet-zero command helps bring wastage
down as the subnet 0 becomes usable with this. Note that wastage due to
subnetting is at its minimum when number of subnets and hosts/subnet
are the same.
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conrad

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Number of posts : 108
Age : 41
Location : Philippines
Registration date : 2008-09-27

PostSubject: Re: IP Subnet Calculation & Design Online Documentation   Thu Nov 27, 2008 3:22 pm

Sample Output 2



Source: This output is obtained by using IP Address
150.150.10.10, VLSM Mask bits 2, 3, and 5, and action "Calculate
Subnetting using VLSM."

-----------------------------------------------------------------------------
IP Class: B IP Address: 150.150.10.10
Mask1 Bits: 2 Subnet Mask1: 255.255.192.0
Mask2 Bits: 3 Subnet Mask2: 255.255.224.0
Mask3 Bits: 5 Subnet Mask3: 255.255.248.0

Subnets for Variable Length Subnet Masking
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Subnet Hosts Hosts Broadcast
Address From To Address

150.150.0.0 150.150.0.1 150.150.63.254 150.150.63.255
150.150.0.0 150.150.0.1 150.150.31.254 150.150.31.255
150.150.0.0 150.150.0.1 150.150.7.254 150.150.7.255
150.150.8.0 150.150.8.1 150.150.15.254 150.150.15.255
150.150.16.0 150.150.16.1 150.150.23.254 150.150.23.255
150.150.24.0 150.150.24.1 150.150.31.254 150.150.31.255
150.150.32.0 150.150.32.1 150.150.63.254 150.150.63.255
150.150.32.0 150.150.32.1 150.150.39.254 150.150.39.255
150.150.40.0 150.150.40.1 150.150.47.254 150.150.47.255
150.150.48.0 150.150.48.1 150.150.55.254 150.150.55.255
150.150.56.0 150.150.56.1 150.150.63.254 150.150.63.255
150.150.64.0 150.150.64.1 150.150.127.254 150.150.127.255
150.150.64.0 150.150.64.1 150.150.95.254 150.150.95.255
150.150.64.0 150.150.64.1 150.150.71.254 150.150.71.255
150.150.72.0 150.150.72.1 150.150.79.254 150.150.79.255
150.150.80.0 150.150.80.1 150.150.87.254 150.150.87.255
150.150.88.0 150.150.88.1 150.150.95.254 150.150.95.255
150.150.96.0 150.150.96.1 150.150.127.254 150.150.127.255
150.150.96.0 150.150.96.1 150.150.103.254 150.150.103.255
150.150.104.0 150.150.104.1 150.150.111.254 150.150.111.255
150.150.112.0 150.150.112.1 150.150.119.254 150.150.119.255
150.150.120.0 150.150.120.1 150.150.127.254 150.150.127.255
150.150.128.0 150.150.128.1 150.150.191.254 150.150.191.255
150.150.128.0 150.150.128.1 150.150.159.254 150.150.159.255
150.150.128.0 150.150.128.1 150.150.135.254 150.150.135.255
150.150.136.0 150.150.136.1 150.150.143.254 150.150.143.255
150.150.144.0 150.150.144.1 150.150.151.254 150.150.151.255
150.150.152.0 150.150.152.1 150.150.159.254 150.150.159.255
150.150.160.0 150.150.160.1 150.150.191.254 150.150.191.255
150.150.160.0 150.150.160.1 150.150.167.254 150.150.167.255
150.150.168.0 150.150.168.1 150.150.175.254 150.150.175.255
150.150.176.0 150.150.176.1 150.150.183.254 150.150.183.255
150.150.184.0 150.150.184.1 150.150.191.254 150.150.191.255
150.150.192.0 150.150.192.1 150.150.255.254 150.150.255.255
150.150.192.0 150.150.192.1 150.150.223.254 150.150.223.255
150.150.192.0 150.150.192.1 150.150.199.254 150.150.199.255
150.150.200.0 150.150.200.1 150.150.207.254 150.150.207.255
150.150.208.0 150.150.208.1 150.150.215.254 150.150.215.255
150.150.216.0 150.150.216.1 150.150.223.254 150.150.223.255
150.150.224.0 150.150.224.1 150.150.255.254 150.150.255.255
150.150.224.0 150.150.224.1 150.150.231.254 150.150.231.255
150.150.232.0 150.150.232.1 150.150.239.254 150.150.239.255
150.150.240.0 150.150.240.1 150.150.247.254 150.150.247.255
150.150.248.0 150.150.248.1 150.150.255.254 150.150.255.255
-----------------------------------------------------------------------------


Understanding: Top four lines show the basic information
like the IP Address and VLSM Mask bits entered by user, and the IP
class and masks calculated.

The table that follows shows subnet information similar to SAMPLE
OUTPUT 1. It also shows that the major net is divided in 4 subnets due
to the mask bits 2. Each of the subnets is divided in 2 sub-subnets due
to mask bits 3 (or we can say the major net is divided in 8 subnets).
Each sub-subnet is divided into 4 sub-sub-subnets due to mask bits 5
(or we can say that the major net is divided into 32 subnets).

Once this division is understood, a network planner can use a subnet
in one portion of the network with more users, and a sub-subnet out of
another subnet in some portion of the network with less users. Note
that if a subnet has been used in one portion of the network, its
sub-subnets or sub-sub-subnets shouldn't be used in other portions of
the network. Good planning should lead to logically easy route
summarizations.

Error Messages & Warnings



Errors



Address can't start with a 0.
An IP Address input with first byte zero has been entered.
This is not a class A, B, or C address. So 0.50.33.5 will cause this
error.

Address is missing.
IP Address input has not been specified. It is required for all actions.

Address or Mask has illegal characters.
An IP Address, Address Mask, or VLSM Mask input has characters
other than decimal numbers or dots (even spaces are not allowed). So
123.123.!23.123 will cause this error.

Address or Mask has illegal numbers.
An IP Address, Address Mask, or VLSM Mask input has a number
greater than 255. This is not allowed as each number in IP address
represents one byte which can store a maximum decimal value of 255. So
255.255.256.0 will cause this error.

Address or Mask too long.
An IP Address, Address Mask, or VLSM Mask input string passed
from HTML browser to CGI script has more than normal size (16
character, like 255.255.255.255 plus the NULL string terminator). So
123.123.123.1234 will cause this error.

HTML input variable string is too long.
The total HTML string (including variable names, values, and
special characters) sent from HTML browser to the CGI script is more
than normal length (I chose 1000 characters for no special reason). As
the tool's user interface will not generate such a long string, this
error message should never show up. If it does show up, then user may
have pressed too many spaces in some input box, or Web is just going
crazy, or in worst case CGI server is out of mind.

Mask is missing.
Address Mask input has not been provided by user when action
"Find IP Subnet for this address" or "Calculate All IP Subnets" is
chosen. This input is required for specified actions.

Mask is not good.
An Address Mask, or VLSM Mask input doesn't contain a valid
mask. For example, 255.0.255.0 will cause this error. In this case,
mask is not too long, contains no illegal numbers or characters,
however, it is not contiguous.

Minimum subnets or hosts/subnet entry is missing.
Minimum Subnets or Minimum Hosts/Subnet input has not been
provided by user when action "Design IP Subnetting (maximize subnets)",
"Design IP Subnetting (maximize hosts)", or "Design IP Subnetting
(minimize wastage)" is chosen. This input is required for specified
actions.

No Action selected.
None of the possible actions has been selected by user. An action must be selected for achieving results.

Something is really wrong!
This message is in the CGI script for second level checking.
During any operation the first level checking (which generates all
other error messages and warnings) should catch all errors and
exceptions, and this message should not show up at all. If it does show
up, reload the tool from HTML browser, as it is due to the browser
sending illegal data to the CGI script.

Subnets or Hosts are zero or invalid.
Minimum Subnets or Minimum Hosts/Subnet input provided by user
is either zero or an illegal character, when action "Design IP
Subnetting (maximize subnets)", "Design IP Subnetting (maximize
hosts)", or "Design IP Subnetting (minimize wastage)" is chosen. This
input should be a non zero decimal number for specified actions
(especially Minimum Subnets input; CGI script may work around Minimum
Hosts/Subnet being zero). If you want your Minimum Hosts/Subnet
requirement to be regardless of Minimum Subnets, then use 1 as Minimum
Subnets.

VLSM masks are missing.
None of the three VLSM Masks have been provided by user, when
action "Calculate Subnetting using VLSM" is chosen. This input is
required for specified action.


Warnings



Either there are no usable hosts, or no usable subnets.
The inputs and action are such that number of hosts or subnets
is zero or less). For example, class C IP Address 200.200.200.0 and
Address Mask 255.255.255.254, with action "Calculate All IP Subnets"
will cause this warning. This is because out of the only two hosts
possible in any subnet, one is the subnet address and the other is
broadcast address for that subnet.

No Subnetting Used.
The inputs and action are such that number of bits in classful
mask is zero. For example, class C IP Address 200.200.200.0 and Address
Mask 255.255.255.0, with action "Calculate All IP Subnets" will cause
this warning.

Your desired minimum subnets and hosts requirement not met.
Minimum Subnets or Minimum Hosts/Subnet input provided by user
is such that it can't achieved for the given IP Address, when action
"Design IP Subnetting (maximize subnets)", "Design IP Subnetting
(maximize hosts)", or "Design IP Subnetting (minimize wastage)" is
chosen. For example, a network IP Address 200.200.200.0, Minimum
Subnets 14, and Minimum Hosts/Subnet 20 will cause this error. This is
because we need at least 16x32 = 512 addresses to meet the minimum
requirements (used 16 and 32 because they fall on the next bit
boundary), while class C networks have at most 256 addresses.
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