Doubt in Subnets

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Hello,
I am a little confused. Let's say there is one big network - 192.168.0.0/24 (XYZ corporation). I decide to break it down into 2 subnets by changing the subnet mask to /25 as XYZ corporation had 2 departments on the floor namely, IT and Finance. The 2 networks are; 192.168.0.0/25 - 192.168.0.127/25 (IT) & 192.168.0.128/25 - 192.168.0.255/25 (Finance). Now do these 2 subnets of 2 different departments need separate routers of their own or can it have a common router and 2 separate switches? Actually, I am unable to relate the functionality of the switch to the concept of subnetting. So my question in short is, when we do subnet on a larger network, do we need switches to separate these new subnets, or do we need routers? Do switches have any relation/connection with IP address based division of network?

Hey @Atharva-Bet another good question, the switches need a connection to the router that will route traffic between the 192.168.0.0/25 IT network and the 192.168.0.128/25 Finance network, however the switches do not see the IP layer, they instead recognize the MAC addresses of the routers interfaces (or individual routers) and send the data based on the Layer 2 information. The router will process the information that is sent by the switch based on the routers MAC address. Then when the processing moves up to the IP layer (Layer 3), the router will see the destination IP address is not the routers and check it's own routing table to determine whether the data is being sent to 192.168.0.0/25 network or the 192.168.0.128/25 network and choose the interface connected to the appropriate network.

Hello @wes-bryan Sir, Thanks for calling it a good question, I really appreciate it. I did understand the first part of what you said but I'm still unable to comprehend whether when a single big network when subnetted into 2 smaller networks, these 2 individual networks require their own separate routers right?
I'll attach a pic of what I understood. Please check it and correct me if necessary.

Also, under a single router, if we isolate some hosts under 2 different switches, that is not subnetting right?? If that is not subnetting, then what is it?
Thanks..

You will need one of two things

1 - router with two NICs, one connected to each network
2 - two routers, one connected to 192.168.0.0/25 and one connected to 192.168.0.128/25

When you divide the network with switches you are create network segments based on physical connections or network segmentation
Another way to divide the networks at the switching layer is to create a VLANs. This is a way that the switch can act as though it is multiple individual switches.

When you divide the network by routers you are dividing it based on logical divisions or subnets using IP addresses and software.

@wes-bryan, Thank You, Sir, I got it now. So it's our choice right whether to divide a bigger network with either routers or switches? Is one of them better than the other? Like in my case I could keep both the IT and Finance Departments under a single router by assigning separate switches to them and also what I could've done is that to assign separate routers to both departments giving them one switch each under their own respective router right? Both of these kinds of divisions could have got the job done right?

@Atharva-Bet said in Doubt in Subnets:

Hello,
I am a little confused. Let's say there is one big network - 192.168.0.0/24 (XYZ corporation). I decide to break it down into 2 subnets by changing the subnet mask to /25 as XYZ corporation had 2 departments on the floor namely, IT and Finance. The 2 networks are; 192.168.0.0/25 - 192.168.0.127/25 (IT) & 192.168.0.128/25 - 192.168.0.255/25 (Finance). Now do these 2 subnets of 2 different departments need separate routers of their own or can it have a common router and 2 separate switches?

On a router, each interface connects to a different subnet. So you do not need 2 different routers you can connect to different subnet via 1 router (Layer 3 device). If you have multiple devices within a single subnet, you may want a switch to connect all of those devices that are on the same subnet.

Actually, I am unable to relate the functionality of the switch to the concept of subnetting. So my question in short is, when we do subnet on a larger network, do we need switches to separate these new subnets, or do we need routers? Do switches have any relation/connection with IP address based division of network?

There two primary reasons to subnet within a company. ONE, you have 1 large address space you can use but this only gives you one network and you need to make more than ONE but smaller networks. That is the first reason. Two, the other reason is because you're not wanting to use the entire address spaces as ONE single network and want to conserve the space and use only what is necessary.

Either way, because subnets are Layer 3 divisions you need routers.

• Routers separate Layer 3 broadcast domains
• Switches do not separate broadcast domains.