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I am new to Subnetting a network so please bear with me. I understood all theory but not able to find any information or tutorials that can explain practical steps and configuration require to achieve this. I want to divide my home network into two sub-nets. The gateway address is 192.168.1.1 and mask is 255.255.255.0. To divide it into two sub-network I understand that the mask need to be 255.255.255.128. But I can't get any help on internet about how to configure the routers for this? Do I need 3 routers for 2 sub-nets? If yes, what would be the network address and Mask on each router. I am happy to be corrected on my above understanding and would appreciate any help or link to resource. Please note that I have access to 3 router in total.

Update: More information:

This is something I want my network:

network 1

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  • What router do you have? Most enterprise routers are able to subnet. Aug 21, 2018 at 6:25
  • I have a D-link ADSL2 router. It is a basic home router. Sorry, I am not sure if I need a enterprise router to be able to subnet my home network.
    – akajain
    Aug 21, 2018 at 6:26
  • can you please post the exact model? Aug 21, 2018 at 6:27
  • What kind of connection and separation do you want between your subnets?
    – RalfFriedl
    Aug 21, 2018 at 6:29
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    Please edit your question and explain how your network looks like. The usual rule is one subnet per LAN segment. If you just have one LAN segment, two subnets are a bad idea. If you want "virtual" subnets on a single LAN segment, have a look at VLAN tagging. In any way, please describe your main goal: Why do you think you need two subnets?
    – dirkt
    Aug 21, 2018 at 7:51

2 Answers 2

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A router is a device that connects two or more networks. If you want two networks, there is no need for three routers, also no obvious benefit.

If you want to experiment and learn, I recommend getting a cheap router that is supported by OpenWRT. OpenWRT is a Linux system designed for routers. Most home routers already run a Linux system, but it is usually locked down by the vendor and less flexible.

You could also see whether you can run OpenWRT on your main router, but I don' recommend that, if you misconfigure your router, you won't be able to search the internet for help.

With an additional router, you can split your internal network in two, one part between the main router and the second router, the other part behind the second router. You can connect your second router to the main router and have two subnets behind the second router. You can setup iptables to allow or deny access between the networks as you like.

If you want just a guest Wifi, You can also get a simple router, use the manufacturer's NAT configuration, connect your devices to the new router and the router together with the guests to the main router. You can also reverse the configuration, but without additional blocking, devices in the second router have access to devices on the main router.

Regarding subnets, the only requirement is that they don't contain public addresses and that they are distinct.

You can have one subnet 192.168.1.0/25, this includes the addresses from 192.168.0.0 to 192.168.0.127, although the lowest and the highest address are not used. Similarly you can have the other subnet 192.168.1.128/25, this includes the addresses from 192.168.1.128 to 192.168.1.255. But as you can use the whole private address space, you can also use 192.168.2.0/24 for your second subnet.

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You don't subnet a network, you subnet a network block. If you want to two devices to connect to each other without a router between them, they should be on the same network.

If you want to have two subnets, 192.168.1.0/25 and 192.168.1.128/25 then you don't want a physical network numbered 192.168.1.0/24 because that would include both blocks in the same physical network.

Instead, change router A's LAN side to something else. For example, you could configure router A's LAN side to 192.168.9.1/24. That creates a new network to connect the three routers and you could assign router B the address 192.168.9.2/24 on that network and router C can be 192.168.9.3/24 on that network. Now, router A is routing between the 192.168.9.0/24 network and the 192.168.1.0/25 network. The 192.168.9.0/24 network services to interconnect the routers.

For this to work, however, you would need all three routers to understand how to route to all the networks involved. For example, routers A and B would need a route to 192.168.1.128/128 through 192.168.9.3 so they know to forward traffic to hosts on that subnet to router C. You can do this with static routes or using a dynamic routing protocol like OSPF.

This will be a fairly complex network to manage and maintain, and giving Internet access to the 192.168.1.128/128 network and 192.168.1.0/128 networks will require configuring some device to NAT for them.

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