Understanding IEEE 802.1Q Standard in Switched Environments | Cisco Exam 200-125

IEEE 802.1Q Standard

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In a switched environment, what does the IEEE 802.1Q standard describe?



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A. B. C. D. E.


A broadcast domain must sometimes exist on more than one switch in the network. To accomplish this, one switch must send frames to another switch and indicate which VLAN a particular frame belongs to. On Cisco switches, a trunk link is created to accomplish this VLAN identification. ISL and IEEE 802.1Q are different methods of putting a VLAN identifier in a Layer 2 frame. The IEEE 802.1Q protocol interconnects VLANs between multiple switches, routers, and servers.

With 802.1Q, a network administrator can define a VLAN topology to span multiple physical devices.

Cisco switches support IEEE 802.1Q for FastEthernet and Gigabit Ethernet interfaces. An 802.1Q trunk link provides VLAN identification by adding a 4-byte tag to an Ethernet Frame as it leaves a trunk port.

The IEEE 802.1Q standard is a protocol used to implement Virtual LAN (VLAN) tagging. In a switched environment, VLANs enable network administrators to segment the network into multiple virtual networks that are isolated from each other, providing security and improved network performance.

When a packet is sent from a device in one VLAN to a device in another VLAN, it needs to cross a trunk link that connects the switches. The 802.1Q standard defines a method for tagging Ethernet frames with VLAN identification information as they traverse the trunk link. This tagging enables the receiving switch to identify which VLAN the frame belongs to and forward it appropriately.

In summary, the IEEE 802.1Q standard describes a method of VLAN trunking that enables the transport of VLAN information across a switched network. Therefore, option B, "a method of VLAN trunking," is the correct answer. The other options are not related to the IEEE 802.1Q standard.

A. The operation of VTP (VLAN Trunking Protocol) is not described by the IEEE 802.1Q standard, but VTP is a Cisco proprietary protocol that enables the propagation of VLAN information across a switched network.

C. The IEEE 802.11 standard describes wireless LAN communication, not the 802.1Q standard.

D. Root bridge selection is a process used in Spanning Tree Protocol (STP), which is not related to the IEEE 802.1Q standard.

E. VLAN pruning is a feature that enables a switch to limit the traffic it sends over a trunk link to only the VLANs that are necessary, reducing unnecessary traffic. However, VLAN pruning is not the main function of the IEEE 802.1Q standard.