Module 6 - Ethernet Channel

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?

• Traffic can only be sent to two different switches if EtherChannel is implemented on Gigabit Ethernet interfaces.​

• Traffic can only be sent to two different switches if EtherChannel is implemented on Layer 3 switches.​

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

• Traffic cannot be sent to two different switches, but only to two different devices like an EtherChannel-enabled server and a switch.​

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.

Which statement is true regarding the use of PAgP to create EtherChannels?

• 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.

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.

What are two requirements to be able to configure an EtherChannel between two switches? (Choose two.)

• The interfaces that are involved need to be contiguous on the switch.

• All the interfaces need to work at the same speed.

• All the interfaces need to be working in the same duplex mode.

• All interfaces need to be assigned to different VLANs.

• Different allowed ranges of VLANs must exist on each end.

Answer explanation

All interfaces in the EtherChannel bundle must be assigned to the same VLAN or be configured as a trunk. If the allowed range of VLANs is not the same, the interfaces do not form an EtherChannel even when set to auto or desirable mode.

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

• The EtherChannel bundle is down.

• The EtherChannel bundle is operating at both Layer 2 and Layer 3.

• Two Gigabit Ethernet ports are used to form the EtherChannel.

• 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.

Which two parameters must match on the ports of two switches to create a PAgP EtherChannel between the switches? (Choose two.)

• MAC address

• speed

• VLAN information

• PAgP mode

• port ID

Answer explanation

For an EtherChannel to be created, the ports that are concerned on the two switches must match in terms of the speed, duplex, and VLAN information. The PAgP mode must be compatible but not necessarily equal. The port ID and the MAC addresses do not have to match.

What are two load-balancing methods in the EtherChannel technology? (Choose two.)

• combination of source port and IP to destination port and IP

• source IP to destination IP

• source port to destination port

• combination of source MAC and IP to destination MAC and IP

• source MAC to destination MAC

Answer explanation

Depending on the hardware platform, one or more load-balancing methods can be implemented. These methods include source MAC to destination MAC load balancing or source IP to destination IP load balancing, across the physical links.

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

• active

• auto

• on

• desirable

Answer explanation

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

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

• The interface port-channel number has to be different on each switch.

• The switch ports were not configured with speed and duplex mode.

• The switch ports have to be configured as access ports with each port having a VLAN assigned.​

• 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.

Which mode configuration setting would allow formation of an EtherChannel link between switches SW1 and SW2 without sending negotiation traffic?

• 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

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.

Which two channel group modes would place an interface in a negotiating state using PAgP?

(Choose two.)

• on

• desirable

• active

• auto

• passive

Answer explanation

There are three modes available when configuring an interface for PAgP: on, desirable, and auto. Only desirable and auto place the interface in a negotiating state. The active and passive states are used to configure LACP and not PAgP.