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192.168.x.x network larger than 254 hosts?

Posted on 2010-09-03
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Last Modified: 2012-05-10
Hi, I need to extend an existing Class C network (192.168.0.0/24) to allow about 3-400 hosts.
Is it ok to set the subnet mask to /23 (thus allowing 510 hosts) but keep the IP numbers in the 192.168.x.x range?

I would get the usable range 192.168.0.1 to 192.168.1.254 but I dont know if that is 'legal' in a local addressing scheme.

Would it be better to switch to a 172. or 10. scheme? I would rather keep it at 192.168.x.x so that devices with fixed IP's don't need configuring.

Bit rusty with all this Networking gubbins :)
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Question by:MereDevelopment
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12 Comments
 
LVL 57

Expert Comment

by:giltjr
ID: 33596117
With VLSM you can change it to /23, however you will need to change the subnet mask on every device that current has it set to /24.

However, why do you want to do this?  I personally think it would be better to have two /24's and us a router to route traffic between the two subnets when needed.

Unless there is a technical reason they must be on the same subnet, have multiple smaller subnets is better than having fewer larger subnets.
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LVL 2

Expert Comment

by:jtokarchuk
ID: 33596260
Not that I am questioning you, giltjr, but why would you want to NAT over multiple subnets? Just curious, is all. Thanks!
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LVL 57

Expert Comment

by:giltjr
ID: 33596693
Please point out to me where I mentioned doing NAT'ing?

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LVL 9

Assisted Solution

by:ffleisma
ffleisma earned 100 total points
ID: 33597067
no problem changing your mask to accommodate the extra host. Using variable masks doesn't restrict you to use 172.16 or 10. networks, you can apply 255.0.0.0 mask on a 192.x private network.

for you subnetting needs you can use free tools/subnet calculators, link below is one you can download, very useful.

http://www.solarwinds.com/products/freetools/free_subnet_calculator.aspx 
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LVL 1

Assisted Solution

by:cyazares
cyazares earned 100 total points
ID: 33597386
Yes, 192.168.0.0/23 is "legal"; 192.168.0.0/16 - 30 is usable as well. But like giltjr said, changing the mask on every device would be necessary.
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LVL 24

Expert Comment

by:rfc1180
ID: 33598442
>Would it be better to switch to a 172. or 10. scheme? I would rather keep it at 192.168.x.x so that devices with fixed IP's don't need configuring.

No, but for many not very familiar with subnets, classful/classless routing, etc, it can be a bit difficult to understand "What should I use". It is perfectly legal to increase your subnet mask from a /24 to a /23. This is called supernetting and not VLSM. So with the being said along with the other comments, you should be set to increase the mask and ensure that all your hosts and other network devices have been updated along with any NAT statements that you might have defined as well as any static/dynamic routing in your network.

Good Luck
Billy
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LVL 57

Expert Comment

by:giltjr
ID: 33598592
It is both VLSM and supernetting.  Supernetting is one of the two things you can do when you do VLSM.

VLSM is using subnet masks that do not conform to the old "classfull" subnets. You can either increase the number of hosts by reducing the number of bits used for the mask or decrease the nubmer of hosts by increasing the number of bits used for the mask.


Increasing the number of hosts is supernetting (fewer bits in the mask).   Decreasing the number of hosts is just further subnetting (more bits in the mask).
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LVL 24

Expert Comment

by:rfc1180
ID: 33598875
Interesting:
>It is both VLSM and supernetting
http://en.wikipedia.org/wiki/Supernet

"A supernet is an Internet Protocol (IP) network that is formed from the combination of two or more networks (or subnets) with a common Classless Inter-Domain Routing (CIDR) routing prefix."

http://www.softpanorama.org/Net/Transport_layer/subnetting_and_vlsm.shtml

It is not both VLSM and supernetting, I am not trying to be argumentative, simply ensuring that the correct information is being conveyed.

Billy
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LVL 57

Expert Comment

by:giltjr
ID: 33599024
Maybe is just the way I under stand it.

From Protocol Requirments in the wiki link on Supernet:

Supernetting requires the use of routing protocols that support variable length subnet masking (VLSM) and the Classless Inter-Domain Routing (CIDR) method.


Meaning with VLSM there is no supernetting.
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LVL 57

Accepted Solution

by:
giltjr earned 150 total points
ID: 33599060
That was supposed to say:

Meaning withOUT VLSM there is no supernetting.

Although the the original purpose of VLSM was to sub-divide classfull subnets, it also became the basis of supernetting.
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LVL 24

Assisted Solution

by:rfc1180
rfc1180 earned 150 total points
ID: 33599073
>Meaning with VLSM there is no supernetting.
Agreed, and we can continue with an open dicussion after the issue has been resolved as it is really not important to the solution, it is just a matter of terminology and how it is applied in a discussion.

Billy
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LVL 1

Author Closing Comment

by:MereDevelopment
ID: 33622464
Ok thanks all. Bit difficult to award points on this one as it went a bit freeforall in the middle there. Thanks for being a bit pedantic Billy, sometimes it is important to state exactly the technically accurate thing.

So now I understand that, as there is a nice logical place to split into 2 subnets I think I'll do that. Glad to know that super-netting is possible in the way I wanted to do it though, cheers!
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