Lan Switches Flashcards

Which Spanning Tree Protocol feature allows a port to immediately transition to the forwarding state when connected to an end device?

Answer: PortFast

PortFast skips the listening and learning STP states so end-device ports forward immediately without waiting the standard 30 seconds.

A switch receives a frame with a destination MAC address not found in its CAM table. What action does it take?

Answer: Floods the frame out all ports except the ingress port

When a destination MAC is unknown, the switch floods the frame out all ports in the same VLAN except the port it arrived on — this is called unknown unicast flooding.

Which EtherChannel negotiation protocol is Cisco proprietary?

Answer: PAgP

Port Aggregation Protocol (PAgP) is Cisco's proprietary protocol for negotiating EtherChannel link bundles, whereas LACP is the IEEE 802.3ad standard.

In PVST+, which switch is elected as the root bridge for each VLAN?

Answer: The switch with the lowest bridge ID (priority + MAC)

The root bridge is elected as the switch with the lowest bridge ID, which is the combination of the bridge priority and MAC address.

Which command configures a switch port as an 802.1Q trunk that allows all VLANs?

Answer: switchport trunk encapsulation dot1q followed by switchport mode trunk

You must first set the encapsulation to dot1q, then set the mode to trunk; without both commands the port does not become an active 802.1Q trunk.

What is the default STP port cost for a 1 Gbps link using the IEEE short path cost method?

Answer: 4

Using the IEEE 802.1D short (16-bit) path cost method, a 1 Gbps link has a default cost of 4.

Which switch security feature limits the number of MAC addresses learned on a port and disables the port on violation?

Answer: Port Security

Port Security allows you to restrict the number of valid MAC addresses on a port and choose a violation action such as shutdown.