VLANs

dpathi

Hi All,

Need help to understand the following on VLANS

1) Can a single VLAN contain multiple subnets? If yes, are all such subnets belong to the same broadcast domain?

2) Can a single Subnet contain multiple VLANs? If yes, are all such VLANs belong to the same broadcast domain?

Thx

shiju_v

You can have multiple subnets in a VLAN. This will act like having multiple subnets in one plain and default switch/hub. In this case the broadcast should be limited to each subnet theoretically.

For your second question, theoretically yes. IPs of a subnet can be distributed in two VLANs. However systems within the same VLAN can communicate. But cannot communicate with ones outside the VLAN, though they all looks like a part of the subnet. The communication between the VLANs may happen if both the VLAN are interconnected. This design is not good.

dpathi

Thx for helping.

dontstop

shiju_v wrote: »

In this case the broadcast should be limited to each subnet theoretically.

VLAN aside, let's say all devices are connected to just a dumb switch. Even with different subnets wouldn't all of these hosts be in the same bcast domain? A layer 2 broadcast will be seen by all hosts connected to the same VLAN as it's flooded on all interfaces regardless of their logical layer 3 addressing.

dpathi wrote: »

1) Can a single VLAN contain multiple subnets? If yes, are all such subnets belong to the same broadcast domain?

I'd say yes you can have multiple Subnets in a single VLAN, but I'd also say this is not an optimal configuration. All hosts would be in the same broadcast domain as there is no router to separate the layer 2 broadcasts.

shiju_v

Very true. Thanks for clarifying the Layer-2 broadcast situation. ARP plays a major role.