Confused about Subnets and VLANS 1

[pst133ox]

I've been looking into expanding my network from 172.16.1.X to 172.16.0.0-172.16.3.255 (mask of 255.255.252.0?) to allow for the future expansion of my network. I am confused about whether or not the subnets need to be on their own VLAN or if with those settings they will be able to communicate with one another.

Perhaps I'm missing something.

 

[brianinms]

Usually a subnet corresponds to a vlan. Such that subnet 10.150.10.0 255.255.255.0 would be VLAN 10, and 10.150.11.0 255.255.255.0 would be VLAN 11. I would never recommend a subnet larger that a 255.255.255.0 or /24 bit for a lan subnet.

 

[pst133ox]

Ah, so setting up VLANs would just be setting up identical networks (with 255.255.255.0) that are capable of transmitting data to one another rather than getting confused about their destination. Why would you not recommend larger than /24 for a LAN? Is my vision of expanding the subnet range and allowing for additional devices (i can't imagine adding more than a few hundred over the next few years) to communicate with each other an incorrect one?

 

[LawnBoy]

I use /16 subnets frequently.

I'm a little confused by your question, you say you want to expand your subnet and then you talk about subnets(plural). If you expand a subnet, you still only have one subnet... not many subnets...

Perhaps I misunderstand.



"We must fall back upon the old axiom that when all other contingencies fail, whatever remains, however improbable, must be the truth." - Sherlock Holmes

 

[lhuegele]

Basically what VLAN's give you is some routing capabilities at the switch layer. It gives you some level of routing control between different subnets within the same physical location without having to buy and use expensive routers.

For example, we have some servers on a 192.168.x.x subnet (255.255.0.0) and some on a 167.116.x.x subnet. These two subnets use the same switch so we set-up a 192 VLAN and a 167 VLAN on that switch to give us the control we needed. We also designated a gateway port on that switch that everyone uses. It's pretty cool actually.

Good luck,

 

[brianinms]

I don't recommend using any mask larger than a /24 because its industry practice not to have more than 150 hosts per network segment.

 

[pst133ox]

So you just leave 103 would-be host spots empty?
Maybe I'm thinking about doing things the wrong way.

My current network is 172.16.1.X with a subnet mask of 255.255.255.0. I've run out of space on the network.

I thought the solution was to change the network mask to allow for a wider IP address range. (Say from 172.16.1.X - 172.16.2.X)

Am I going about this the wrong way?

 

[pagy]

What you could do is change your subnet mask to 255.255.254.0 this would give a host address of 172.16.0.1 - 172.16.1.254 or 510 hosts, this also would give 128 additional subnets if you ever needed future expansion again.

BTW - Someone please check my maths, I did this in my head and my subnetting is never great

I personally like to keep it 510 hosts per subnet maximum when possible. That is just personal preference, I know some people who have 1024 or more hosts on subnets.

Paul
MCSE


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[brianinms]

Pst, you can do that , but I certainly wouldn't recommend it. Nor would I ever recommend having more than 200 hosts on a subnet.

 

[LawnBoy]

The plan in your original post will work fine. You will not need to create any VLANs to make it work.

"We must fall back upon the old axiom that when all other contingencies fail, whatever remains, however improbable, must be the truth." - Sherlock Holmes

 

[lhuegele]

It really depends on how robust the rest of your network infrastructure is, like your switches, etc. Way back when, we started seeing issues on our backbone switches as we moved beyond 400 devices on the same subnet. Also, having everything in one big subnet like that made it next to impossible to track down problem devices that were maybe flodding the network with broadcast traffic. We are now in the middle of a huge network refresh project and we are sub-netting out our site (we have 3 buildings on one class B subnet at the moment) to finally address those issues.

So, you can change your subnet to make more addresses available to your network, but you will have a trade-off's in network stability down the road as you saturate your network gear with broadcast traffic.

Good luck,

 

[pst133ox]

So I'm approaching a time when I actually have time to execute this plan. I'm projecting after a thorough device count that I will only need room for X.X.1.1-254 and X.X.2.1-254

Anyone think it's worth the trouble to segment the floors of the building into VLANS to easily identify rogue broadcast noise?

 

[dearingkr]

OK, I guess I'll add my 2cents...

First off, you can expand your subnet as planned.
It is the easiest and cheapest way to go.
However, there are some factors you should consider.

A subnet that large will have significant broadcast traffic which will, of course, affect performance.
Assuming you're using 10/100 switches, you need to consider bandwidth requirements.
It will also be more difficult to manage and troubleshoot if a problem arises.

I agree with braininms, more than 200 devices on one subnet and you're asking for problems.

By breaking up your network into smaller subnets, it makes management and troubleshooting much easier. You can better mitigate bandwidth issues.

The downside to smaller subnets is that you'll need a router or layer-3 capable switch to route traffic between the subnets.

Another thing to consider is security. By segmenting your network, you can set up better access control to sensitive devices and data.

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