# Subnetting: Accommodate more than 225 hosts

Registered Users Posts: 3 ■□□□□□□□□□
Hi,

I have a subnetting question. First I’ll give an example:

An organization has the IP 200.1.1.0 and needs 4 subnets with the following characteristics:

Subnet A =>72 hosts

Subnet B => 35 hosts

Subnet C => 20 hosts

Subnet D => 18 hosts

Provide the IPs per subnet.

Solution

Subnet A =72 host

For 72 hosts we need 2^7 - 2 = 128 - 2 = 126 host. We need 7 bits for the hosts.

Network => 200.1.1.0/25

First Host => 200.1.1.1/25

Last Host => 200.1.1.126/25

Subnet B =35 host

For 72 hosts we need 2^6 - 2 = 64 - 2 = 62 host. We need 6 bits for the hosts.

Network => 200.1.1.128/25

First Host => 200.1.1.129/26

Last Host => 200.1.1.190/26

Subnet C =72 host

For 72 hosts we need 2^5 - 2 = 32 - 2 = 30 host. We need 5 bits for the hosts.

Network => 200.1.1.192/27

First Host => 200.1.1.193/27

Last Host => 200.1.1.222/27

Subnet D =72 host

For 72 hosts we need 2^5 - 2 = 32 - 2 = 30 host. We need 5 bits for the hosts.

Network => 200.1.1.224/27

First Host => 200.1.1.225/27

Last Host => 200.1.1.254/27

So, according the above solution, how do we create subnets for the IP 155.52.48.0/23 with the following characteristics (provide Network, Mask First Host, Last Host and Broadcast IPs foe each subnet)?

Subnet A =>200 hosts

Subnet B => 100 hosts

Subnet C => 40 hosts

Subnet D => 40 hosts

I’m really stuck with that.

• Member Posts: 21 ■■□□□□□□□□

[TH]Subnet Name[/TH]
[TH]Needed Size[/TH]
[TH]Allocated Size[/TH]
[TH]Assignable Range[/TH]

A
200
254
155.52.48.0
/24
255.255.255.0
155.52.48.1 - 155.52.48.254
155.52.48.255

B
100
126
155.52.49.0
/25
255.255.255.128
155.52.49.1 - 155.52.49.126
155.52.49.127

C
40
62
155.52.49.128
/26
255.255.255.192
155.52.49.129 - 155.52.49.190
155.52.49.191

D
40
62
155.52.49.192
/26
255.255.255.192
155.52.49.193 - 155.52.49.254
155.52.49.255

• Registered Users Posts: 3 ■□□□□□□□□□
What I don't understand is the "Network Address" part.
Is it valid from address 155.52.48.xxx to go to 155.52.49.xxx?
Could you please explain me the "mechanics" of that approach?
• Member Posts: 423
I don't know if it'll help you, but I'm working on tying to explain the "mechanics" of Subnets and have just put together this URL="http://rob42.net/IPv4_Subnets1.htm"]Rob42.net - IPv4 Subnets[/URL. I'd appreciate any feedback on my work.

It's a work in progress...
No longer an active member
• Member Posts: 1,046 ■■■■■■■■□□
anarchos78 wrote: »
What I don't understand is the "Network Address" part.
Is it valid from address 155.52.48.xxx to go to 155.52.49.xxx?
Could you please explain me the "mechanics" of that approach?

It's all about understanding how to identify the "octet of interest".
Once you know the octet, everything else falls into place.

155.52.48.0/23 = 155.52.48.0 - 155.52.49.255
its not much to explain; you just have to practice subnetting /16 - /23.

I learned subnetting from Danscourses:
Watch video# 47.
(after you "get" it; give him a Thumbs-UP)

As for the rest of your Q:
200 hosts = a blocksize 256.
aka: 2^8
aka: /24
This means it falls under the 4th octet.
so your 200 hosts would fit on the subnet: 155.52.48.[0-255]

Your next subnet starts at 155.52.49.0
(because there is no more room inside 155.52.48.x ).

B = 155.52.49.[0-127]
C = 155.52.49.[128-191]
D = 155.52.49.[192-255]

just takes practice..
• Registered Users Posts: 3 ■□□□□□□□□□
Thank you very much!