I have use three switches, and three different networks. In one switch, there are four PCs connected with two VLANs. I do the same thing to the other two switches, and I use trunks to connect the switches. I sent packets to another network using same VLAN ID, but the packets failed to reach the destination.
How do I send the packets?
When a host sends traffic destined for a different network, it sends it to it configured gateway (usually a router), which is the host on a LAN that knows how to forward the traffic toward the destination network.
A host will compare its network with the destination network by masking the source and destination addresses on the layer-3 packet to see if they are on the same network. If the source and destination addresses on the layer-3 packet are in the same network, the host will encapsulate the the layer-3 packet in a layer-2 frame with the address of the destination host. If the networks are different, when the host will encapsulate the layer-3 packet in a layer-2 frame with the layer-2 address of its configured gateway.
That means that traffic sent to a different layer-3 network will be sent directly to the gateway, not the destination host.
In order for you to send traffic from one network to a different network, you need a router that knows how to get to each network.
