Computer Networking Basics
On one L2 switch, VLANs are configured so that ports 1–4 are in VLAN 10 and ports 5–8 are in VLAN 20. Which statement about its operation is correct?
- ABecause VLAN 10 and VLAN 20 are on the same switch, they can communicate directly without a router
- BSplitting into two VLANs halves the speed of each port
- CBroadcasts sent by devices in VLAN 10 do not reach VLAN 20 ports, and traffic between VLAN 10 and VLAN 20 needs a router (or L3 switch)
Show answer and explanation
Answer: C. Broadcasts sent by devices in VLAN 10 do not reach VLAN 20 ports, and traffic between VLAN 10 and VLAN 20 needs a router (or L3 switch)
A VLAN (virtual LAN) creates logically separate networks on the same physical equipment, typically on a per-port basis. Each VLAN has its own broadcast domain, the range a broadcast reaches, and the switch forwards frames only between ports in the same VLAN. Traffic between different VLANs, such as VLAN 10 and VLAN 20 in this example, must therefore pass through a router or L3 switch that relays it at layer 3. When VLANs span several switches, a tag (VLAN ID) defined by IEEE 802.1Q is inserted into frames to indicate which VLAN they belong to. VLANs are used to separate networks by department, or to isolate a guest wireless LAN from the internal network.
- A. The switch does not forward directly between different VLANs, so relaying at layer 3 is needed.
- B. A VLAN is a logical division; port speeds do not change.
- C. Correct. Each VLAN is a separate broadcast domain.