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TOPIC: IP addressing advice

Re: IP addressing advice 15 years 7 months ago #3573

  • Jbull
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Thanks for the terrific answer and diagram. So I understand that you advise in favor of multiple subnets at each location rather than 1 large one at each of the locations. Does this require more effort on the part of the router, since it would be routing between the internal subnets in additional to its job of natting and and then routing between the other routers in our WAN?


You mentioned that your ISP has configured your network routers with IP addresses falling in the 10.x.x.x range, so your surely talking about your network's internal LAN as this range is excluded from the Internet's routers.

Networks such as 10.x.x.x, 172.16.x.x and 192.168.x.x. are only for private use and non-routable to the Internet.

From your description, I have understood that your network is quite big, 15 sites, each one with two networks using a 24 bit subnet mask (, connected to your head office, which is running out of IP addresses.

If this is correct, then here's what I suggest:

Any network, should be restricted to a certain amount of hosts. It is surely not a good idea placing 500 hosts, whether they are workstations or other network aware devices, on one physical or logical network if your not using some type of smart LAN technology - for example, VLANs.

The reason you shouldn't place so many hosts are quite a few. The most important though are 1) Broadcasts and 2)Security.

Having too many windows (especially) workstations on one network is a nightmare. Essentially what will happen is they will be flooding your network with broadcasts, chewing up your bandwidth!

The second reason is quite obvious and doesn’t need any clarification :)

Before you start breaking networks and assigning new IP addresses, I'd recommend you to take a look at your network infrastructure and see if there is any possibility of creating VLANs. Unfortunately I am in the process of analysing the topic at the moment and won't have it complete anytime soon, so I can't refer you to any internal page, but there is heaps of information on them on the Internet should you wish to learn more about them.

In the case VLANs are not a solution, then you need to break the network. The best, and safest way to do this is to physically break the networks between each other.

To help you get a visual on what I'm talking about, I've included the diagram below, which is from the VLAN topic I'm writing:

As you can see, there needs to be some type of router that will route packets from one network to another. This can be in form of a physical router .e.g Cisco router or a PC with routing enabled.

If you need more information, just give us some type of diagram with the networks involved so the answer can be specific to your network.


Re: IP addressing advice 15 years 7 months ago #3575

Yep the router would have additional work to do with the inter-subnet routing.. however if its a half decent router it should have no trouble doing this.
Sahir Hidayatullah. Staff - Associate Editor & Security Advisor

Re: IP addressing advice 15 years 7 months ago #3599

  • Jbull
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Thanks, they're Cisco 1700s.
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