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I have 6 sites all connected via a 20mb fiber ring. There is 1 dhcp server and wan connection at site1 and the netblock is which is enormous. As you can tell all sites grab an IP from site1 and the only issue is when site1 goes down so do all of the sites.

What I want to do is introduce VLAN into the scenario and set the other 4 sites up with a separate neblock. This way we can move print servers, dhcp servers, etc to each location so if something goes down they can still function. Each switch in all sites have an IP of 1.1.X.3. What do you guys recommend? Should we make the current netblock small and reconfigure everything? (which is a lot of downtime) or should we take the next netblock after the /16 and create /24's for each site? Or maybe neither?

Also should the IP's of the other switches change? Thanks.

Thank in advance.

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You REALLY do want to use VLANing in this scenario, otherwise broadcast traffic will eat up all of that precious 20Mb you have.

You will want to assign each VLAN at least one separate IP network (the term netblock isn't used by anyone by the way), though you can have a single central DHCP server using what's known as a 'DHCP helper" on your router. You don't provide any details about the number of devices at each site but using a /24 for each VLAN is very commonly used and easy to manage, it also happens to match most people's suggested VLAN size limit too. I'm going to assume the '1.1.X.3' bit meant '1*0*.1.X.3' in which case that sounds sensible.

Basically you're on the right track, obviously you don't discuss what you're doing for routing and that'll take a good chunk of time and thought but essentially you're doing the right things.

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There are less than 100 devices per location. We are using 3com 4500G switches to do the routing. I'm still unsure If I need to change the IP's of the switches at each site. Some of the switch IPs are,, etc. Do I need to have a vlan ip or can everything be routed to the internet to which is the current gateway. – nennis2k4 Apr 27 '12 at 10:05
You would want each site to have its own IP range / subnet as well as its own vlan. As such subnet will need a local gateway defining for it, and routing will need to be enabled between each subnet. – RobM Apr 27 '12 at 10:17
okay that makes sense. should the switches on each site have it's own IP? right now all switches are apart of the /16 since it's 1 big network – nennis2k4 Apr 27 '12 at 10:32
Yes, they will. – Chopper3 Apr 27 '12 at 10:34
Whats your thoughts on the following networks Shrinking the original network to this after new sites are added Adding these to the sites – nennis2k4 Apr 27 '12 at 19:32

The best way to go at this in my opinion would be to have the default gateway for the machines inside the subnet handle the vlan routing, if you add the vlan as an interface to the router and set up open routing between the current /16 network and the new /24 network you can seamlessly transfer clients by just changing the vlan for their network port (of course you would have to renew their IP)

so the steps would be. 1. add the vlans to the switches 2. configure the router to route between vlans 3. configure DHCP and the likes on all new vlans 4. reconfigure the vlans on the ports of the client PC's (and change/renew ip configuration) 5. reconfigure the vlans for the servers (and change/renew ip configuration)

if all above done remove the old vlan.

As far as the switches go, we have a router for each site, there for our "management lan" which holds switch management, router management etc. needs a seperate subnet on each site. I do think this is best practice to have it like this.

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Whats your thoughts on the following networks Shrinking the original network to this after new sites are added Adding these to the sites – nennis2k4 Apr 27 '12 at 19:32
The size of the subnets and the number of subnets are impossible for me to tell. Obviously subnets shouldnt be much larger then the space actually requires, the amount of subnets required obviously relates to the number of sites you have, and the number plan is something you have to device yourself, as long as you document it properly it should be no problem to expand or change in the future, good luck ! – Flash May 2 '12 at 12:40

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