You can think of a VLAN as a network if that helps. So where I work we have all kinds of networks, ones for PLCs, Servers, Networking Devices, Wireless, etc. To make things easy with our networking environment we created VLANs for each one of these. This way we can have multiple devices from each main category connected to any switch we want but we can have that device in it’s own VLAN.

In other words, without VLANs you would need a lot more networking devices because each access layer switch would have to be on it’s own network, just like your home network. Any switch(es) you plug into your router or modem at home is going to be on the same network. With VLANs we can plug a server, PLC, regular user, and wireless AP into the same switch if needed and still have them all be in their respective VLANs.

VLANs themselves do not have IPs assigned to them like computers and servers do. Instead they are assigned networks. Which is why many people exchange the word VLAN for network and vice versa. So at home your probably have a 192.168.0.0 255.255.255.0 network or something similar. Well for VLANs we do the same thing…

We might assign 192.168.1.0 255.255.255.0 to servers, 192.168.2.0 255.255.255.0 to PLCs, 192.168.3.0 255.255.255.0 to regular users, and 192.168.4.0 255.255.255.0 to wireless. This means a server will get a different IP than a PLC, etc. Thus our segregation with VLANs. And if you understand how IPs and Subnet masks work, you will know that each VLAN above will have its own network and communication and be separate from each other.

Your IP you mentioned above, 192.168.4.100 255.255.255.0, is likely an IP within a VLAN and not a gateway for that VLAN or anything like that. Typically the gateway is the first or last usable IP in the network range but it doesn’t have to be. The broadcast address is always the last IP in the range and can never be assigned to anything, in your case the broadcast IP would be 192.168.4.255.

I hope this ramble helps…

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