Configuring an EtherChannel Bundle: LACP Detection Mode

LACP Detection Mode

Question

When configuring an EtherChannel bundle, which mode enables LACP only if a LACP device is detected?

Answers

Explanations

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A.

The LACP is Link Aggregation Control Protocol.

LACP is an open protocol, published under the 802.3ad.

The modes of LACP are active, passive or on.

The side configured as passive will waiting the other side that should an Active for the Etherchannel to be established.

PAgP is Port-Aggregation Protocol.

It is Cisco proprietary protocol.

The mode are On, Desirable or Auto.

Desirable " Auto will establish an EtherChannel.

An example of how to configure an Etherchannel: SwitchFormula1>enable - SwitchFormula1#configure terminal SwitchFormula1(config)# interface range f0/5 -14 SwitchFormula1(config-if-range)# channel-group 13 mode ? active Enable LACP unconditionally auto Enable PAgP only if a PAgP device is detected desirable Enable PAgP unconditionally on Enable Etherchannel only passive Enable LACP only if a LACP device is detected.

When configuring an EtherChannel bundle, there are two protocols that can be used for negotiation: Port Aggregation Protocol (PAgP) and Link Aggregation Control Protocol (LACP).

PAgP is Cisco's proprietary protocol, while LACP is the industry-standard protocol.

To answer the question, the mode that enables LACP only if a LACP device is detected is the "Passive" mode.

When using LACP, there are two modes that a port can be configured with: Active or Passive.

  • Active mode means that the port will always send LACP packets to negotiate the EtherChannel bundle.
  • Passive mode, on the other hand, means that the port will wait to receive LACP packets before starting negotiations.

If a device that is not running LACP is connected to a port in Passive mode, then no negotiations will occur, and the port will function as a standalone link.

In summary, if you want to use LACP for negotiation, you should configure the port in Passive mode. However, if you want to use PAgP, then you should configure the port in either Desirable or Auto mode.

Desirable mode means that the port will actively attempt to negotiate a PAgP EtherChannel bundle, while Auto mode means that the port will wait for the other end to initiate the negotiation.

The "On" mode, as the name suggests, forces the port to always be a member of the EtherChannel bundle, without any negotiation.

Lastly, Active mode means that the port will always send LACP packets to initiate the negotiation.