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What would be the best, or easiest, way of increasing the number of IP addresses we have at our disp

We have a single class C network with the default subnet mask. Because we are continually adding machines and devices,...

we will soon run out of IP addresses. What would be the best, or easiest, way of increasing the number of IP addresses we have at our disposal, and how would we go about doing this? In today's networks, running out of available IP Addresses is a common problem, especially for medium to large sized companies.

If your company maintains a simple network infrastructure, then overcoming the problem will at most times be a simple and straight forward process. This is the case for the majority of companies.

On the other hand, if your dealing with a large, complex network with remote offices, then it gets quite complicated!

Whichever the case, don't despair as there is an answer to every problem. The key component to your success in the less stressful manner is the method you will use to approach your solution, and that's what we are going to talk about now.

Considering you're the network administrator of the company, you will need to follow a few simple steps to find out which way would be the best to resolve the problem. Here are a few major points which will help you understand what to do:

  1. Company's departments
    Note down the company's department and the amount of users each one contains. This will help you figure out how much spare IP Addresses you need to plan for the future.
  2. Switches, routers, etc.
    Note down the number of active connectivity devices used on the network. This includes routers, switches, printers and other devices which use IP Addresses.
  3. Remote networks
    Does your company have any remote networks/branches? If so, note them down and also examine if there are any NAT (Network Address Translation) performed by any router or server for these remote networks. Some companies have hosts on remote networks appear as valid local IP addressees, therefore we must take them into consideration
  4. RAS dialups
    Do you use any Remote Access services? If so, note down the number of IP Addresses reserved for these
  5. Servers
    Here is where you note all the servers used on your local network.

By now you should have a rough idea on the current requirements your network has. The next step would be to break each point to analyze each point and create a network for them (where applicable) but also keeping in mind the following:

  1. Never include more than 40-50 workstations on one logical/physical network. This will create a number of problems such as broadcast storms, possible network loops and overall slowdown of the network.
  2. Routing. When breaking one network into smaller ones, we must keep in mind that should these networks require communication between each other, we will need to route packets between them. The easiest way to do so would be using a layer 3 switch. These awesome devices have routing capabilities so you are not required to have a physical router.
  3. DHCP/Static IP's. If our network policy defines static IP Addresses, assigning them to our hosts will be an easy task. If on the other hand we require a DHCP server, we can enable one DHCP server for each logical network.

Another neat solution is the creation of VLANs. VLANs are cool and will enable you to create separate logical and physical networks, using one physical switch!

I've written a white paper on VLANs that outlines what they are, the different configurations they support and will help you get some good in-depth information about them. Of course, each VLAN will be configured with its own network, so VLAN 10 could be network, VLAN 11 would be, VLAN 12 and so on. Again, the switches would handle the internal routing between these VLANS.

As you can see, there are quite a few options available for you. The most basic setup would be splitting your existing network into smaller logical ones and enabling routing between them by using a layer 3 switch or a Windows/Linux server.

The more complicated (and coolest!) option would be to create a VLAN for each network and perform routing on a layer

This was last published in December 2003

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