1.VLANs can communicate with other VLANs when they both using the same trunk linkto connect to the same layer 2 switch
No, not possible on the same switch. Trunk is used to connect to other switch and then Sw1 Vlan x can connect to Vlan X on sw2. In case When you use same cable to connect 2 ports on different vlan on same switch, protection kicks in -see below ad.3.
2.VLANs with the same default gateway can communicate with other VLANs under the same layer 2 switch
No, remember L2 switch forwards traffic based on destination MACs and its own MAC address table (vlan id, port, MAC). switches will build such forwarding table based on source MAC. this also means that any unknown traffic (MAC is not in table) will be flooded to all ports in that Vlan x and over the trunk ports that allow Vlan x to pass. Normally vlans should be on different subnets and have different default gateways (matching subnet).
3. native VLAN can access other VLANs under the same layer 2 switch
There is native vlan hack when u connect 2 switches with cable and those 2 corresponding ports are in different native vlan id. Then, communication leaks between vlans because tag is striped due to native vlan id. When you connect 2 ports in the same switch with cable. however, there is switch protection (i forgot name of it) that put one of ports into error-disabled state and communication is stopped. you must disabled
Regards, ML
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