192.168.x.x network larger than 254 hosts?

Hi, I need to extend an existing Class C network ( 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 to 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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giltjrConnect With a Mentor Commented:
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.
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.
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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Please point out to me where I mentioned doing NAT'ing?

ffleismaConnect With a Mentor Senior Network EngineerCommented:
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 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.

cyazaresConnect With a Mentor Commented:
Yes, is "legal"; - 30 is usable as well. But like giltjr said, changing the mask on every device would be necessary.
>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
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).
>It is both VLSM and supernetting

"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."


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

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.
rfc1180Connect With a Mentor Commented:
>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.

MereDevelopmentAuthor Commented:
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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