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Additional Subnet or Supernet?

Posted on 2011-09-16
Medium Priority
Last Modified: 2012-05-12
     We currently have a bit of a situation on our hands, as we only have 20 or so available IPs left in our network, and we're currently expanding into an office across the parking lot from our current office. My question is twofold, first, what would be the best practice for making additional addresses available? I've heard supernetting isn't a good idea because of the constraints of Ethernet when you have anything more than 254 hosts, and I'm also a bit reluctant to supernet because I'll have to go to all the statically configured machines to adjust their subnet masks. The current range for distribution on our Windows Server 2003 DHCP server is to with an exclusion zone in the middle from to 169. I suppose I could make the new range to, and then add exclusion zones to that, but is that a good idea? Or would I be better served by using an additional subnet with another router? We currently have a SonicWall TZ 170 Enhanced, and I'm not 100% sure how I would configure that, or what kind of additional router I should get. If I do go for another subnet, do I need another DHCP server? Does it need to be placed somewhere else? Are there any considerations for DNS?

Secondly, as far as connectivity goes, we currently have a point to point wireless connection between the two buildings. I didn't put this in and I'm a bit uncomfortable with it. As we expand, I think we may run into bandwidth issues. So my next question is, if I run fiber from one building to another, are there any special considerations? Is it like Ethernet where I can plug one fiber capable switch into another and then run it into our Ethernet switches? Any recommendations on what kind of switch/cabling to get?

Thanks for any help!
Question by:indigo6
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LVL 22

Expert Comment

ID: 36552515
What is the subnet for this network?  That will dictate how many IP addresses you can use.  Increasing the DHCP range to would give you more IP's, but the subnet probably has to be changed for it to work.

Wireless connections between buildings are common when fiber is not available, they are usually reliable as long as the transmitters are mounted well and nothing is blocking the signal.

You shouldn't need to add another router or DHCP server, the 2nd building can run off of the first.

If you want to run fiber, you'd want to use "single mode" cabling and run multiple strands for redundancy.  It's best to bring in a contractor who is familiar with the process.

Author Comment

ID: 36552585
The current subnet mask is I have those upper (200-254) and lower (1-90) addresses excluded from distribution because we use them for statically configured network printers, servers and devices, since we have quite a few statically configured devices, I was thinking the second router/subnet option would work well so I won't have to touch every single one of those statically configured network devices.

I was planning on having the second building run off of the first, and maybe just having a static route between my sonicwall and an additional router which would handle the 10.30.1.x subnet. My question for this second subnet is whether or not I need another DHCP server, or maybe I can use DHCP relay, which I've never done before... Also, would I need to do anything to DNS for the second subnet?

Thanks for the tips on the fiber! I do have one more question on it though, is it just "plug and play" like copper Ethernet?
LVL 22

Accepted Solution

eeRoot earned 750 total points
ID: 36552744
A subnet of means the range is to, so without going to every device to change the subnet, you could create a new VLAN with a new range of IP's.  You don't need to set up a new DHCP server, justa new scope of the existing one and an ip helper address on the sonicwall to direct DHCP requests.  DNS can remain on the existing server, as long as the subnets can communicate with each other.

The section "Configuring Multiple LAN Subnets" in this guide has a good description on how to set up multiple subnets.

Fiber is not exactly plug and play, you have to make sure light is passing through cleanly and make sure the fiber, GBIC, and switch are all compatible with each other.
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Assisted Solution

gmbaxter earned 750 total points
ID: 36553939
What switches do you currently use in location 1?

If location 1 is /24 and it won't grow much (within the building), I'd leave it as it is. Then create a new vlan for location 2: /24 with the same exclusion zones for printers etc if you desire.

That is the most simple way of doing it, the other way would be to increase your existing vlan and DHCP range to be - and subnet mask of (/23). This would require you changing the subnet mask on all static addressed equipment however, so option 1 is best.

As far as fiber is concerned, you should get someone to install and terminate it as already mentioned, then you'll probably need an SFP for each switch. Configure one port on each switch (that the SFP and fiber plug into) to be a trunk port.

Author Comment

ID: 36568944
There are about 5 switches in location 1, a few different kinds, at least 3 of them are managed switches... The primary growth area will be location 2, right now it's a Point to Point wireless connection, I really want to change to fiber, hence the questions about it. I'll definitely be using our wiring contractor for that if we go that way.

We probably won't need exclusion zones so large in the second location. How would I go about creating a second VLAN? Say one scenario being we stay with PTP wireless and the other, we go fiber, would I be able to create the VLAN with PTP wireless? What kind of equipment would I be looking for for both scenarios? The two VLANs could communicate with each other right?

Thank you!

Author Comment

ID: 36577069
Ok, so we will be going with fiber between the two locations. So, the question now becomes, how do I create a VLAN for location 2 and ensure they can both communicate? Thanks again for all the help.
LVL 22

Expert Comment

ID: 36577383
The switch port connections between the buildings need to be set to "trunked mode."  That will allow multiple VLAN's to move across the connections.

Author Comment

ID: 36711936
Ok, I will do that. If they're set in trunked mode, I don't have to create a VLAN right away, right?
LVL 22

Expert Comment

ID: 36713740
No, if no VLAN is set, then the network defaults to VLAN 1

Author Closing Comment

ID: 36815542
Looks like "trunked" mode is the way to go then, that way I can setup a VLAN in the future when I do actually run out of IPs.

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