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VLAN / Subnet Project

I manage a network with about 400 IP devices plugged into to our LAN. I know how to use VLAN's and I have a test environment in place with routing and everything working great.

My final questions before I start breaking our production network down are:

1) At what point is using VLAN's required on a LAN when security isn't a concern on the LAN?

2) Is there a certain number of devices the we should try to stay under per VLAN?

3) Is it possible for the VLAN routing on our backbone to cause noticeable latency?

I'm trying to avoid causing administration overhead where it isn't needed.
 
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MMHDU
Asked:
MMHDU
2 Solutions
 
that1guy15Commented:
1) At what point is using VLAN's required on a LAN when security isn't a concern on the LAN?
 
--VLANS would be required when you have a large number of devices on the same network and broadcast start effecting the network. With your setup of 400 devices all of them could be on the same VLAN and i do not think you would see issues. I would suggest seperating devices into VLANS to keep your network organized.

2) Is there a certain number of devices the we should try to stay under per VLAN?

 -- You do not have anything to worry about with the number of devices you have (400). Like i said above seperate your devices for organization (ie: servers, workstations, building, floor, department. what ever is best for your network)

 3) Is it possible for the VLAN routing on our backbone to cause noticeable latency?

-- No i highly doubt you will see any effect on your network.
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MysidiaCommented:
(3) If  your backbone and the routing scheme is properly designed, no.

(2) 500 - 1000,  depending on how "chatty" your hosts are in terms of broadcasts.
It is best to divide according to security divisions and reliability divisions.

Think of VLAN division as useful for troubleshooting; many problems that occur in
LANs are broadcast-related   and   their effects may be somewhat contained to a VLAN.

(1)  Provided you are using switches and not hubs, at no small point is it an absolute requirement.   I would say in many cases, you can easily put 3000 hosts on a VLAN with no issues, with some caveats.   In most cases, more than 1000 hosts in a VLAN will be significantly inefficient and difficult to troubleshoot if something goes wrong.

With enough hosts, broadcast traffic will take its toll and introduce noticeable CPU overhead to your hosts,  when you have thousands of them.

However if all your hosts are equipped with 100 megabit Ethernet or 1000 megabit Ethernet, and  reasonably fast CPUs, the broadcast traffic is simply negligible,
losing 10 megabits  across every link may not be a big deal.

But overhead may be a hit on busy machines if your hosts run protocols that generate many broadcasts. In general, the number and frequency of broadcasts is slightly more important than their size.

Receiving several thousand broadcasts per second means every CPU on your network will be burning CPU cycles and interrupts to process broadcast packets that could be used for something useful..  not to mention: the waste of electricity.

An examples of protocols you shouldn't allow any host to run on a very large VLAN with thousands of hosts:
* Upnp
* Netware SAP
* RIP
* NetBIOS
* WINS
* Windows computer browser

On a MASSIVE LAN with say >5000 hosts...
Don't run chatty DHCP clients either.

Either use static assignment  (not recommended),
or one-time bootp to give hosts a permanent ip.

or DHCP with very long minimum lease and refresh times.
And beware of any windows services that use broadcasts for discovery...
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