Trunking in 802.1Q: Important Facts and Details

ACE

802.1Q is a standard that defines a method for transmitting VLAN information between network devices. Trunking is a technique used to transport multiple VLANs over a single link between two switches. Here are the three correct statements regarding 802.1Q trunking:

A. 802.1Q native VLAN frames are untagged by default. Native VLAN frames are transmitted without a VLAN tag. By default, frames from the native VLAN are untagged when they traverse a trunk port. The native VLAN is the VLAN that is not tagged on the trunk link. When the switch receives an untagged frame, it associates it with the native VLAN. The native VLAN can be changed, but it is recommended to set the same native VLAN on both ends of the trunk link.

B. 802.1Q trunking ports can also be secure ports. Secure ports are those that restrict the number of MAC addresses that can be learned on a port. 802.1Q trunking ports can also be secure ports. When the port security feature is enabled on a trunk port, it restricts the number of MAC addresses that can be learned for each VLAN on the port.

E. 802.1Q trunks should have native VLANs that are the same at both ends. The native VLAN should be the same on both ends of the trunk link. If the native VLAN is different on each end of the trunk link, it can lead to connectivity issues. For example, if a frame from a non-native VLAN is sent from one switch and received by another switch with a different native VLAN, the frame will be dropped.

The following statements are incorrect:

C. 802.1Q trunks can use 10 Mb/s Ethernet interfaces. 802.1Q trunks require a minimum bandwidth of 100 Mb/s. Therefore, 10 Mb/s Ethernet interfaces cannot be used as 802.1Q trunk ports.

D. 802.1Q trunks require full-duplex, point-to-point connectivity. 802.1Q trunks do not require full-duplex connectivity, although full-duplex is recommended for performance reasons. Trunks can also support multiple VLANs, and therefore, they do not require point-to-point connectivity. However, it is recommended to configure trunk ports as point-to-point links to avoid unnecessary broadcasts.

In summary, native VLAN frames are untagged by default, trunking ports can be secure, and native VLANs should be the same at both ends of the trunk link.