vlan and subnet question

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Jon Marshall Tue, 05/15/2007 - 06:53


No not necessarily. A subnet might not exist as a vlan, it could be a point to point link between 2 routers or L3 switches for example.

But generally a subnet on a L3 switch is tied to a vlan. Even if the L3 interface is on a router, the router interface will connect into a switch. You could then connect hosts into that switch and as long as all the ports are in the same vlan they could communciate with the router etc. Even thoughy you haven't created a vlan interface you are still tying a subnet to a vlan to all intents and purposes.



Danilo Dy Tue, 05/15/2007 - 06:55


If you are only using a switch (L2 or L3) in a network, you need a vlan for every subnet (loopback is a host not a subnet).

However, if your network is mixed switch, router, firewall, and hub. You can create subnet without a vlan, for example the subnet is connected to a hub in which the firewall or router is the gateway. To be able for subnets to reach each other (vlan or no vlan) make sure that you route them properly.


Jon Marshall Tue, 05/15/2007 - 09:07


It's a bit of a difficult one. If you are using a switch even a point to point link will utilise a vlan in one sense ie.

router1 -> -> Switch1 -> (router2)

Even here the two switch ports would need to be in the same vlan.

However if you used a crossover cable to connect the routers or the line was a serial connection between the 2 routers then you would not be using a vlan.

A host connected to a switch would still be in a vlan. A host connected to a hub would not be. A subnet can span multiple hubs without there being a vlan although hubs are not widely used these days.

Hope this clarifies things



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