Cisco WS-SUP32-GE-3B Software Configuration Guide - Page 150

Understanding How EtherChannels Work Chapter 10 Configuring EtherChannels LACP uses the following parameters: • LACP system priority-You must configure an LACP system priority on each switch running LACP. The system priority can be configured automatically or through the CLI (see the "Configuring the LACP System Priority and System ID" section on page 10-10). LACP uses the system priority with the switch MAC address to form the system ID and also during negotiation with other systems. Note The LACP system ID is the combination of the LACP system priority value and the MAC address of the switch. • LACP port priority-You must configure an LACP port priority on each port configured to use LACP. The port priority can be configured automatically or through the CLI (see the "Configuring Channel Groups" section on page 10-7). LACP uses the port priority with the port number to form the port identifier. LACP uses the port priority to decide which ports should be put in standby mode when there is a hardware limitation that prevents all compatible ports from aggregating. • LACP administrative key-LACP automatically configures an administrative key value equal to the channel group identification number on each port configured to use LACP. The administrative key defines the ability of a port to aggregate with other ports. A port's ability to aggregate with other ports is determined by these factors: - Port physical characteristics, such as data rate, duplex capability, and point-to-point or shared medium - Configuration restrictions that you establish On ports configured to use LACP, LACP tries to configure the maximum number of compatible ports in an EtherChannel, up to the maximum allowed by the hardware (eight ports). If LACP cannot aggregate all the ports that are compatible (for example, the remote system might have more restrictive hardware limitations), then all the ports that cannot be actively included in the channel are put in hot standby state and are used only if one of the channeled ports fails. You can configure an additional 8 standby ports (total of 16 ports associated with the EtherChannel). Understanding Port Channel Interfaces Each EtherChannel has a numbered port channel interface. You can configure a maximum of 128 port-channel interfaces, numbered from 1 to 256. The configuration that you apply to the port channel interface affects all LAN ports assigned to the port channel interface. After you configure an EtherChannel, the configuration that you apply to the port channel interface affects the EtherChannel; the configuration that you apply to the LAN ports affects only the LAN port where you apply the configuration. To change the parameters of all ports in an EtherChannel, apply the configuration commands to the port channel interface, for example, Spanning Tree Protocol (STP) commands or commands to configure a Layer 2 EtherChannel as a trunk. Understanding Load Balancing An EtherChannel balances the traffic load across the links in an EtherChannel by reducing part of the binary pattern formed from the addresses in the frame to a numerical value that selects one of the links in the channel. 10-4 Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY OL-11439-03