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general IP subnetting

Posted on 2013-06-07
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Last Modified: 2013-07-09
I want to create a network that I can grow with, want to use class B (/16) subnet with network number 10.10.0.0. I need about 12 networks subnet, several subnets need more than 254 IP (say about 400 IP). Can someone give me a break down of the 12 networks for 10.10.0.0?
thanks
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Question by:officertango
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by:giltjr
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Why do you think you need 400 hosts in the same subnet?  Are they using sometype of non-routable protocol?

Any way, a subnet mask of 255.255.254.0 will give you 510 hosts.

You can start with 10.10.0.0/23 then go to 10.10.2.0/23, then 10.10.4.0/23, continue increasing the 3rd octect by 2 until you have 12.
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by:Sandy
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2^n -2 = 2^4 -2 = 14 networks

10.0.0.0/12

Cheers
SA
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by:officertango
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So if I have 10.106.0.0/16, I can sub net it down to say 10.106.1.0/32 for one network and another say 10.106.2.0/255.255.254.0. Is it bad to have subnet with 510 hosts?

Thanks
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by:giltjr
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Yes you could use 10.106.1.0/24 and 10.106.2.0/23, remember you can also use 10.106.0.0/24.

It's not that it is bad, just that using a /24 (255.255.255.0) is typically easier for most  people to understand and deal with.

You don't know how many times I have had to explain that just because an IP address  is ".0" or ".255" does not mean it can't be assigned to a host or just because an IP address is NOT ".0" or ".255" that it can't be a network/broadcast address.  A lot of people just don't understand what subnet masks are and how they work.

I find it easier just to use /24's and it saves a lot of time and generally makes no real difference.

Since you are going to have multiple subnets, you are going to have a "router."  Since you are going to have a router there is no reason to use a /23 unless you are using a protocol that can't be routed, like NETBIOS.  I would suggest that instead of getting  "real router" that you get a L3 switch.  L3 switches "route" L3 traffic just as fast as they switch L2 traffic.
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by:naderz
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In your original post you had mentioned 10.10.0.0 and then later 10.106.0.0. I am going to go with your latest: 10.106.0.0

Minor note on Class terminology: Class B addresses are within the range : 128.0.0.0 to 191.255.255.254. A 10.106.0.0 is actually a Class A address. Your 10.106.0.0 would a subnet withing the Class A. Not important, but then again.

If you start with 10.106.0.0 and use /24 subnet mask across the board you will end up with subnets: 10.106.0.0 through 10.106.255.0 with each subnet having 254 host addresses. That's 256 subnets (counting subnet 0).

That should be your template for your network allowing you to grow as needed.

From there you can change the subnet mask to increase or decrease the number of host.

What you have to remember and make sure you have planned well is where the subnet's host addresses start and where they end.

For example:

Subnet 1 =>   10.106.1.0/24   Hosts: 10.106.1.1 to 10.106.1.254 (254 addresses)
Subnet 2 =>   10.106.2.0/24   Hosts: 10.106.2.1 to 10.106.2.254 (254 addresses)

Subnet 3 =>   10.106.3.0/23   Hosts: 10.106.3.1 to 10.106.4.254 (510 addresses)

Subnet 4 =>   10.106.5.0/24   Hosts: 10.106.5.1 to 10.106.5.254 (254 addresses)

Subnet 5 =>   10.106.6.0/23   Hosts: 10.106.6.1 to 10.106.7.254 (510 addresses)

Subnet 6 =>   10.106.8.0/25   Hosts:  10.106.8.1 to 10.106.8.126 (126 addresses)

Subnet 7 =>   10.106.8.128/25 Hosts:   10.106.8.129 to 10.106.8.254 (126 Addresses)

Subnet 8 =>   10.106.9.0/24   Hosts:   10.106.9.1 to 10.106.9.254 (254 addresses)


Next one can start at 10.106.10.0 and so on depending on the subnet mask.
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by:officertango
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How did you know 10.106.0.0 is class A? Should I not subnet anything greater than 254 hosts of I  have layer 3 switch to route vlan.
Thanx to help me understand
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by:naderz
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By RFC 791 definition:

Class A    0.0.0.0       to   127.255.255.254
Class B    128.0.0.0   to   191.255.255.254
Class C    192.0.0.0   to   223.255.255.254

And, there are more Classes. See: Classful Networks

But, that does not mean you can use a 10.x.x.x however you want. You will be using it in what is known as "classless" fashion. That is perfectly fine. If you were to use a routing protocol on a Cisco router or L3 switch, you would have to specify "ip classless". So, if you are using a Cisco device (L3 switch or router) make sure that command is there even if you are not routing with a routing protocol. It should be default.

You can have as many variation as you want within the big subnet; e.g in this case 10.106.0.0, as long as you plan everything correctly and there are no overlaps. See my previous note.

You just need to plan everything on paper first and make sure the subnets start and end on the correct host IPs.
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by:TomRScott
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Also check out RFC 1918:
http://tools.ietf.org/html/rfc1918

Search for "Private Address Space" and you will find the address blocks reserved for private networking.

This address space is often referred to as "non-routable" as it is NOT supposed to route on the Internet proper, just in private networks allowing these addresses to be reused by private entities (behind firewalls using Network Address Translation) conserving "public" addressing for the public (Internet) arena.
Using the above reference, you will find that for a Class B subnet (16 bit mask) you may use a subnet address template of 172.x.0.0 where x may be in the range of 16-31.

For a "Custom" Class B subnet (17-23 bit mask) you would also use subnet addresses in that range.

 - Tom
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naderz earned 250 total points
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And, you could use 192.168.0.0 (Class C) and subnet as you like with the same example I had posted before. The point is to not get bogged down by terminology but be aware of what they mean so that you can improvise accordingly.
 
You can use 10.106.0.0 just fine as long as you observe the subnettng rules.
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