Module 6 - Ethernet Channel

Front

Refer to the exhibit. The administrator tried to create an EtherChannel between S1 and the other two switches via the commands that are shown, but was unsuccessful. What is the problem?

Back

Traffic cannot be sent to two different switches through the same EtherChannel link.

Answer explanation

An EtherChannel link can only be created between two switches or between an EtherChannel-enabled server and a switch. Traffic cannot be sent to two different switches through the same EtherChannel link.

Front

Which statement is true regarding the use of PAgP to create EtherChannels? Options: It requires full duplex., It is Cisco proprietary., It requires more physical links than LACP does., It increases the number of ports that are participating in spanning tree., It mandates that an even number of ports (2, 4, 6, etc.) be used for aggregation.

Back

It is Cisco proprietary.

Answer explanation

PAgP is used to automatically aggregate multiple ports into an EtherChannel bundle, but it only works between Cisco devices. LACP can be used for the same purpose between Cisco and non-Cisco devices. PAgP must have the same duplex mode at both ends and can use two ports or more. The number of ports depends on the switch platform or module. An EtherChannel aggregated link is seen as one port by the spanning-tree algorithm.

Front

Refer to the exhibit. On the basis of the output that is shown, what can be determined about the EtherChannel bundle?

Back

A Cisco proprietary protocol was used to negotiate the EtherChannel link.

Answer explanation

Two protocols can be used to send negotiation frames that are used to try to establish an EtherChannel link: PAgP and LACP. PAgP is Cisco proprietary, and LACP adheres to the industry standard.

Front

When EtherChannel is configured, which mode will force an interface into a port channel without exchanging aggregation protocol packets?

Back

on

Answer explanation

For both LACP and PAgP, the "on" mode will force an interface into an EtherChannel without exchanging protocol packets.

Front

An EtherChannel was configured between switches S1 and S2, but the interfaces do not form an EtherChannel. What is the problem?

Back

The EtherChannel was not configured with the same allowed range of VLANs on each interface.

Answer explanation

The guidelines for configuring an EtherChannel link are:

Interfaces which form an EtherChannel can be physically discontiguous, and on different modules.

Interfaces in an EtherChannel have to operate at the same speed and in the same duplex mode.

Interfaces in the EtherChannel must be assigned to the same VLAN, or be configured as a trunk.

Interfaces in the EtherChannel have to support the same allowed range of VLANs.

Front

Which mode configuration setting would allow formation of an EtherChannel link between switches SW1 and SW2 without sending negotiation traffic? Options: SW1: on, SW2: on; SW1: desirable, SW2: desirable; SW1: auto, SW2: auto, trunking enabled on both switches; SW1: auto, SW2: auto, PortFast enabled on both switches; SW1: passive, SW2: active

Back

SW1: on, SW2: on

Answer explanation

The auto channel-group keyword enables PAgP only if a PAgP device is detected on the opposite side of the link. If the auto keyword is used, the only way to form an EtherChannel link is if the opposite connected device is configured with the desirable keyword. PortFast and trunking technologies are irrelevant to forming an EtherChannel link. Even though an EtherChannel can be formed if both sides are configured in desirable mode, PAgP is active and PAgP messages are being sent constantly across the link, decreasing the amount of bandwidth available for user traffic.

Front

What happens to an EtherChannel if the physical interface for one of the trunk links changes to a down state?

Back

The EtherChannel will remain functional.

Answer explanation

EtherChannel offers redundancy by bundling multiple trunk links into one logical connection. Failure of one physical link within the EtherChannel will not create a change in the topology and therefore a recalculation by Spanning Tree is unnecessary. Just one physical link must remain operational for the EtherChannel to continue to function.

Front

Refer to the exhibit. A network administrator is configuring an EtherChannel link between two switches, SW1 and SW2. Which statement describes the effect after the commands are issued on SW1 and SW2?

Back

The EtherChannel fails to establish.

Answer explanation

The interfaces GigabitEthernet 0/1 and GigabitEthernet 0/2 are configured "on" for the EtherChannel link. This mode forces the interface to channel without PAgP or LACP. The EtherChannel will be established only if the other side is also set to "on". However, the mode on SW2 side is set to PAgP desirable. Thus the EtherChannel link will not be established.

Front

What change in configuration would correct the problem of an EtherChannel link failing to establish between two switches, SW1 and SW2? Options: Configure SW1 EtherChannel mode to on, Configure SW2 EtherChannel mode to on, Configure SW2 EtherChannel mode to auto, Configure SW2 EtherChannel mode to desirable.

Back

Configure SW2 EtherChannel mode to desirable.

Answer explanation

The EtherChannel mode must be compatible on each side for the link to work. The three modes from PAgP protocol are on, desirable, and auto. The three modes from LACP protocol are on, active, and passive. The compatible modes include on-on, auto-desirable, desirable-desirable, active-passive, and active-active. Any other combinations will not form an EtherChannel link.

Front

A network administrator configured an EtherChannel link with three interfaces between two switches. What is the result if one of the three interfaces is down?

Back

The remaining two interfaces continue to load balance traffic.

Answer explanation

EtherChannel creates an aggregation that is seen as one logical link. It provides redundancy because the overall link is one logical connection. The loss of one physical link within the channel does not create a change in the topology; the EtherChannel remains functional.