Cisco Systems A9014CFD manual Understanding How EtherChannels Are Configured, Mode Description

Chapter 9 Configuring EtherChannels

Understanding How EtherChannels Work

If a segment within an EtherChannel fails, traffic previously carried over the failed link switches to the remaining segments within the EtherChannel. When a failure occurs, the EtherChannel feature sends a trap that identifies the router, the EtherChannel, and the failed link. Inbound broadcast packets on one segment in an EtherChannel are blocked from returning on any other segment of the EtherChannel.

Understanding How EtherChannels Are Configured

This section contains the following topics:

•EtherChannel Configuration Overview, page 9-2

•Understanding Manual EtherChannel Configuration, page 9-2

•Understanding IEEE 802.3ad LACP EtherChannel Configuration, page 9-2

EtherChannel Configuration Overview

You can configure EtherChannels manually or use the Link Aggregation Control Protocol (LACP) to form EtherChannels. The EtherChannel protocols allow ports with similar characteristics to form an EtherChannel through dynamic negotiation with connected network devices. LACP is defined in IEEE 802.3ad.

Table 9-1lists the user-configurable EtherChannel modes.

Table 9-1	EtherChannel Modes
Mode	Description
on	This is the mode that forces the LAN port to channel unconditionally. In the on mode, a
	usable EtherChannel exists only when a LAN port group in the on mode is connected to
	another LAN port group in the on mode. Because ports configured in the on mode do not
	negotiate, there is no negotiation traffic between the ports. You cannot configure the on
	mode with an EtherChannel protocol.
passive	(Default for LACP) LACP mode that places a port into a passive negotiating state, in which
	the port responds to LACP packets it receives but does not initiate LACP negotiation.
active	LACP mode that places a port into an active negotiating state, in which the port initiates
	negotiations with other ports by sending LACP packets.

Understanding Manual EtherChannel Configuration

Manually configured EtherChannel ports do not exchange EtherChannel protocol packets. A manually configured EtherChannel forms only when you enter configure all ports in the EtherChannel compatibly.

Understanding IEEE 802.3ad LACP EtherChannel Configuration

LACP supports the automatic creation of EtherChannels by exchanging LACP packets between LAN ports. LACP packets are exchanged only between ports in passive and active modes.

The protocol learns the capabilities of LAN port groups dynamically and informs the other LAN ports. Once LACP identifies correctly matched Ethernet links, it facilitates grouping the links into an EtherChannel. The EtherChannel is then added to the spanning tree as a single bridge port.

Cisco ASR 901 Series Aggregation Services Router Software Configuration Guide

9-2 OL-23826-09