When to start sub-netting

I'm wondering if you're asking about segmenting rather than subnetting. You need to subnet when you either run out of IP addresses on a subnet (254 addresses on a Class C, 65,533 on a Class B), when you have a WAN involved, or when you want to segregate certain functions for security reasons.

From the information you've shared already, you should ideally already have a second subnet for your servers that are visible to the outside world. For security reasons, it's usually best to place outside accessible servers in a "DMZ" or network segment from which an outside user cannot reach your internal network. So that might be one reason to subnet.

However, if you're really talking about segmenting, when to create a new segment depends on your network architecture and how it compares to the physical location of your functional workgroups. If you already have a fully-switched network (i.e. no hubs), and if your servers are already on the same switch as the users associated with thatserver, you've already effectively segmented your network.

To move beyond that, you would probably want to look at implementing VLANs, particularly as you grow past 250 users. At that point, a VLAN implementation will provide both subnetting andsegmentation.

I know this isn't a complete answer but I hope it provides a start.

regards!

paul

In general you add segments when

a) you can identify groups of users whose traffic is internal to the group, and which does not have a lot of traffic outside the group.

b) you have too many stations for your address range

c) you have too many stations for your segment

d) you have too much traffic on your network and are seeing slowdowns due to collisions, or are seeing very high network utilization

Things to ask yoruself, potential gotchas:

1) What is your traffic level? If you put a performance monitor on the server, for example, what does it see in terms of traffic, collisions, etc.?

2) You do not say if you are at 10 or 100mb. If 10, would switching to 100 solve your problem? If so, how long would the solution be good for?

3) Would using switching hubs solve your problems?

4) Are you using routable IP addresses internally? If so, consider that when you subnet a class C you lose a large number of addresses. You might want to think about using multiple 192.168.x.x nets internally with NAT, keeping one segment with real addresses for your servers.

5) Consider that depending on traffic patterns, sometimes a router between subnets actually BECOMES the bottleneck. If almost all of your traffic is to or from a single server this is likely to happen. (Consider dual-porting the server.)

Clearly you will eventually have to divide your network if it continues to grow. The more you know about your network the easier it will be to decide what to do.Once you know where the traffic on your net is really going, and how much there really is, the timing requirement of the split and the location of the split should become very clear.

Good luck.

I believe your concerns are about performance. With this in mind, you will definitely need to have network monitoring software in place. This is really the only way to know if your network is performing properly and where your bottlenecks exist.

Here is what I recommend:

1. Your network should be fully switched. This is less expensive and more effective than routing between 2 or more LANs. If you are going to spend money upgrading anything, get rid of hubs and replace them with switches.

2. As you aggregate traffic on your network to the backbone, you will need to increase the speed. If the workstations are connected at 10Mbps, then connect the switches at 100Mbps, etc. Finally, if you can afford it, connect your servers to a Gigabit switch. If that is cost prohibitive, then connect them using full duplex 100Mbps ethernet or dual 100Mbps ethernet NICs.

3. If you do subnet, you will need additional routers our router ports. This can be costly and doesn't need to be done if your switches are configured properly.

4. One quick way to get some of the traffic off your LAN is to segment the printers by installing a second NIC in the print server. Assign a separate IP subnet to the printing LAN. This will give you 2 LANsseparated by the print server and keep your printing traffic off your main LAN.

5. Finally, use network monitoring software to find and eliminate your bottlenecks.

I hope this helps.

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