01-13-2014 07:56 PM - edited 03-07-2019 05:32 PM
The question refers to a private network design not connected to the internet (using switches not hub). Does number of users or devices is one of the factors? If so, what range (in qty) that when exceeded is best recommended to do subnetting?
01-14-2014 08:07 AM
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Posting
Yes, number of hosts is the factor. That, and how such hosts operate on the network.
There are scalability issues with many hosts on the same network. The most "important" being broadcast traffic. Each host receives all broadcast packets and each host must examine them.
As a rough rule-of-thumb, the classical Class C network (or newer /24) often was, and still is, a "just right" size for host networks.
01-14-2014 11:30 AM
Antonio
Just to add to Joseph's post.
As Joseph says a class C i usually a good guide although the last place i worked we used /25s for client vlans. If you do decide to subnet (use vlans) then be aware that you then need a device to route between those vlans. This could be -
1) your firewall inside interface although as a general rule, unless you have strict security requirements i personally avoid this
2) a router and you use subinterfaces on the router to route
3) a L3 switch which is by far the commonest solution.
Jon
01-14-2014 06:06 PM
Hi Joseph,
Thanks for the reply.
Say how many busy hosts subnetting is recommended? Number please....
01-14-2014 06:15 PM
Say how many busy hosts subnetting is recommended?
Not an easy question. Heck, this is a loaded question.
Your question is talking about WIRED. You're not talking about WIRELESS.
Depends on the size of the organization, really. Rule-of-Thumb, if you are talking about wired, is start with /24. I would normally allow up to 200 hosts. Some networks separate printers with PCs.
Wireless is different. Particularly when you are dealing with Guests access. I have seen wireless network as large as /16 for guest access in a mall.
01-15-2014 02:54 AM
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Posting
If you're using switches, "busy" doesn't matter much regarding number of hosts. Again, it's how the host operate, especially with broadcast traffic.
A /24 provides 254 host IPs, so as Leo notes, often that's used for 200 hosts (leaving some growth room).
The /25 that Jon mentioned, supports 126 host IPs, so for those you target about 100 hosts.
PS:
BTW, Leo mentions much larger address blocks for wireless clients, this because they often don't do "broadcast" like wired hosts.
01-15-2014 07:52 PM
Thank you guys for the replies.
From the replies to the main question, it looks "broadcast traffic" is the main reason to do subnetting? Would this mean that for 200 hosts for example, broadcast traffic is not yet an issue? hence subnetting is not necessary and /24 is perfectly fine?
Thanks again.
01-16-2014 02:16 AM
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The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
Yes, yes and yes.
Remember, though, this is an "it depends" kind of answer.
Also, another issue with larger network address blocks might be multicast. If your switches do not support something like IGMP snooping, multicast is distributed to every port. (I.e. without something like IGMP snooping, a switch behaves much like a hub with this kind of traffic.) One difference about multicast, your NIC can often analyze the multicast packet and determine it's of no interest, similar to how a NIC will ignore unicast packets that aren't addressed to it. So, although the host may not need to fully process the multicast packet, the packet still consumes bandwidth to the port.
10-27-2015 05:10 AM
Hi
according to me the answer of this question is as follows.
we use sub netting when we have very few no. hosts or devices and available IP addresses are very large .... we also use sub netting when no. of hosts and devices are to large and we are configuring logical broadcast domain by using VLAN so in this case we use sub netting .
1. If we have a large no. of IP address range but we have very few no. of hosts or devices . the we can use sub-netting in this case to save the unassigned IP address for other networks.
for example: if we have only two devices in our network and we are using class c address i.e: 192.168.1.0 then we can accommodate 254 hosts and devices in our network. but in our case we have only 2 devices so the large no. of IP addresses are going to be wasted here. to eliminate this wasting of IP address we can use sub-netting. after sub-netting if we use the sub-net mask 255.255.255.252 or /30 the no. of usable IP addresses will be only 2.
2. if the range of users and devices is to large then we use VLAN and VLAN is only accommodate different network so we use sub netting in to logically dividing the IP addresses. there is no any specific range (in qty) to do sub-netting.
Thanks and Regards
Amritpal singh
Spooster IT services
11-06-2015 11:24 AM
Number of Host and number of siwtch ports will define the subnetting
11-07-2015 05:51 PM
To me the factors for subnetting are
1. The number of hosts (it is generally not recommended to exceed the class C subnet limitations, i.e 252 hosts)
2. The need to limit or propagate broadcast and multicast traffic
3. Security factors (one or few subnets can be treated as security zones, with access-lists or firewall inspection between them)
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