Class A ip instead of class C

Posted on 2011-03-08
Last Modified: 2012-06-21
Well I am using class C ip in my network and actually I running out of space. I do not want to subnet kinda too much work. Can I just use A class A ip in my network to be able to accomodate more computer in my network. If yes do I need a particular router? What are the downside of using class A instead of class C
Thank you
Question by:rogergoudiaby
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LVL 35

Accepted Solution

Ernie Beek earned 125 total points
ID: 35069753
Class A might be a bit too big. Normally you wouldn't want more than about 512 nodes in a subnet (broadcasts and other overhead data transmissions).
And nowadays we have CIDR ( so you could just make your current subnet a bit bigger without having to go to class A straight away.

Just go from /24 to /23 and you allready double the amount of available ip's.

Expert Comment

ID: 35070054
According to Cisco, there should not be more than 500 users in one can have /23 subnet...if you go beyond will be slow coz of broadcast traffic...
LVL 13

Assisted Solution

kdearing earned 125 total points
ID: 35070541
Agree with shubhanshu_jaiswal

I prefer to take it a step further.
Anytime you outgrow a Class C, it's time to subnet (VLAN)

There are several advantages to subnetting your network, mainly:
Performance (as erniebeek says)
Security; set up rules to keep people out of HR resources, for example
Maintenance/Troubleshooting; it's much easier to track down problems on smaller subnets
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LVL 29

Expert Comment

ID: 35071088
I wouldn't even go 512,...Cisco's CCNA material when I got my CCNA said that Ethernet looses efficiency around 250-300.  If you ran 512 most likely your 100mbps LAN would run like a 10mbps LAN or if it was a Gig LAN it would probably only perform like it was 100mbps.
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 125 total points
ID: 35071701
In a switched network, since there are no collisions, it's rather difficult to identify a number of devices as a limiting factor.  Normally, broadcasts are used to identify capacity.

The general rule of thumb is 20%. So when broadcast traffic exceed 20% of total traffic, that's the point at which you need to consider breaking up the broadcast domain.

Some O/S's use broadcasts more than others which is why it's difficult to nail down a specific number of devices that a network can tolerate.

LVL 29

Assisted Solution

pwindell earned 125 total points
ID: 35071762
Yea, I think the OS is a factror.  I did a little searching in the forums on and one thread said if there is a lot of Windows OS's then figure around 200+/- which is what I always say,...but if it is moslty *NIXs then you might get away with 512 but you would likely take a performance hit as the subnet started to fill up.

Expert Comment

ID: 35101906
Nobody seems to have asked yet, but what's your network architecture? I don't know why you say sub-netting is too much work, but in general, unless you're running a massively parallel cluster, it's actual likely to be time saving and performance enhancing. How many routers/switches are you dealing with? What type/models? Are the users organized differently than the physical location that prevents logical grouping? What's your expected maximum users/nodes for the foreseeable future? The answer is going to be different if it's under 1000 versus over 10,000.

LVL 70

Expert Comment

ID: 35349330
This question has been classified as abandoned and is being closed as part of the Cleanup Program. See my comment at the end of the question for more details.

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