1

There is an example in 'Computer Network : A top down approach' : how to calculate IP address of the network from the parent network using subnet numbers: Parent Network(Parent ISP)'s IP Address 200.23.16.0/20 There are 8 child organizations below 'Parent Network(Parent ISP)'

  1. Org1's one : 200.23.16.0/23

  2. Org2's one : 200.23.18.0/23

  3. Org3's one : 200.23.20.0/23

  4. Org4's one : 200.23.22.0/23

  5. Org5's one : 200.23.24.0/23

  6. Org6's one : 200.23.26.0/23

  7. Org7's one : 200.23.28.0/23

  8. Org8's one : 200.23.30.0/23

I understand this example easy to understand.

But How about this situation that Org2's subnet number is 24 so that Org2 has more larger network addresses but fewer host addresses(2^8).

Org2's one may be this : 200.23.18.0/24

But there are two cases for next one, Org3.

If we set Org3's one as same as above (200.23.20.0/23), we lost 2^9 - 2^8 IP addresses which is 200.23.19.0/24

So when we consider the lost addresses(=200.23.19.0/24) and recalculate economical Org3, Org3's one is this :(200.23.19.0/24 + 200.23.20.0/24)

But I don't know how to mark 'economical' Org3 as dotted decimal IP address.

What is the solution for this situations having different subnet number at the same level of network depth?

Ron Maupin
  • 99,565
  • 26
  • 120
  • 195
LKM
  • 121
  • 1
  • 3
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide your own answer and accept it. – Ron Maupin Aug 07 '17 at 00:27

3 Answers3

2

I'm not sure I understand you question but the fact is you cannot aggregate in a single prefix 2 subnets from 2 different networks.

If org2 need only a /24 network and org3 need a /23 (I.E. 510 hosts in a single network) the simpliest thing is to use 200.23.20.0/23 for org 3 and use the free 200.23.19.024/24 for another customer who also need a only a /24.

Otherwise you can allocate two different /24 to org 3 but once again you cannot aggregate them.

JFL
  • 19,649
  • 1
  • 32
  • 64
1

if you do not want to mix your subnets, you can organize them in the following manner:

  • The sybnets with a mask in / 23 will start from 200.23.16.0/23, and you will increase of 2 for the next subnet: the following will 200.23.18.0/23, etc ...
  • The subnets with a mask on /24 will start from 200.23.31.0/24 24, and you will decrease of 1 for the next subnet: 200.23.30.0/24, etc ....

In this way, you do not mix your networks with different masks.

Technically, it does not change, you just have your networks sorted according to their masks.

Sorcha
  • 276
  • 1
  • 4
0

Time for IPv4 subnetting. For economical use of addresses, you don't order by organisation. You order by the number of addresses needed. Since Org2 needs less, you move it down the list like this:

Org1's one : 200.23.16.0/23

Org3's one : 200.23.18.0/23

Org4's one : 200.23.20.0/23

Org5's one : 200.23.22.0/23

Org6's one : 200.23.24.0/23

Org7's one : 200.23.26.0/23

Org8's one : 200.23.28.0/23

Org2's one : 200.23.30.0/24

And when new Organisations come along you can add something like:

Org9's one : 200.23.31.0/24
Org10's one : 200.23.32.0/25

In this case Org10's range will start at 200.23.32.0 and end with 200.23.32.127. But this is normally within a business/corp or whatever. An ISP won't want to move their structure around whenever a new customer asks for IP's, because it could affect the other organisations, so JFL and Sorcha's solutions could work. Or whatever. They're an ISP. :D

Amateur NetMan
  • 81
  • 6