Table Of Contents

Configuring EtherChannels

Understanding EtherChannels

EtherChannel Overview

Port-Channel Interfaces

Port Aggregation Protocol

PAgP Modes

PAgP Interaction with Other Features

Link Aggregation Control Protocol

LACP Modes

LACP Interaction with Other Features

Load Balancing and Forwarding Methods

Configuring EtherChannels

Default EtherChannel Configuration

EtherChannel Configuration Guidelines

Configuring Layer 2 EtherChannels

Configuring EtherChannel Load Balancing

Configuring the PAgP Learn Method and Priority

Configuring LACP Hot-Standby Ports

Configuring the LACP System Priority

Configuring the LACP Port Priority

Displaying EtherChannel, PAgP, and LACP Status

Configuring EtherChannels

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This chapter describes how to configure EtherChannels on Layer 2 interfaces on the Catalyst 2970 switch. EtherChannel provides fault-tolerant high-speed links between switches, routers, and servers. You can use it to increase the bandwidth between the wiring closets and the data center, and you can deploy it anywhere in the network where bottlenecks are likely to occur. EtherChannel provides automatic recovery for the loss of a link by redistributing the load across the remaining links. If a link fails, EtherChannel redirects traffic from the failed link to the remaining links in the channel without intervention.

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Note For complete syntax and usage information for the commands used in this chapter, refer to the command reference for this release.

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This chapter consists of these sections:

•Understanding EtherChannels

•Configuring EtherChannels

•Displaying EtherChannel, PAgP, and LACP Status

Understanding EtherChannels

These sections describe how EtherChannels work:

•EtherChannel Overview

•Port-Channel Interfaces

•Port Aggregation Protocol

•Link Aggregation Control Protocol

•Load Balancing and Forwarding Methods

EtherChannel Overview

An EtherChannel consists of individual Gigabit Ethernet links bundled into a single logical link as shown in Figure 26-1.

Figure 26-1 Typical EtherChannel Configuration

The EtherChannel provides full-duplex bandwidth up to 8 Gbps (Gigabit EtherChannel) between your switch and another switch or host.

Each EtherChannel can consist of up to eight compatibly configured Ethernet interfaces. All interfaces in each EtherChannel must be configured as Layer 2 interfaces. For Catalyst 2970 switches, the number of EtherChannels is limited to 12. For more information, see the "EtherChannel Configuration Guidelines" section.

If a link within an EtherChannel fails, traffic previously carried over that failed link changes to the remaining links within the EtherChannel. A trap is sent for a failure, identifying the switch, the EtherChannel, and the failed link. Inbound broadcast and multicast packets on one link in an EtherChannel are blocked from returning on any other link of the EtherChannel.

Port-Channel Interfaces

When you create a Layer 2 EtherChannel, a port-channel logical interface is involved. You can create the EtherChannel in these ways:

•Use the channel-group interface configuration command. This command automatically creates the port-channel logical interface when the channel group gets its first physical interface. The channel-group command binds the physical (10/100/1000 ports) and the logical ports together as shown in Figure 26-2.

•Use the interface port-channel port-channel-number global configuration command to manually create the port-channel logical interface. Then use the channel-group channel-group-number interface configuration command to bind the logical interface to a physical port. The channel-group-number can be the same as the port-channel-number, or you can use a new number. If you use a new number, the channel-group command dynamically creates a new port channel.

Each EtherChannel has a port-channel logical interface numbered from 1 to 12. This port-channel interface number corresponds to the one specified with the channel-group interface configuration command.

Figure 26-2 Relationship of Physical Ports, Logical Port Channels, and Channel Groups

After you configure an EtherChannel, configuration changes applied to the port-channel interface apply to all the physical interfaces assigned to the port-channel interface. Configuration changes applied to the physical interface affect only the interface where you apply the configuration. To change the parameters of all ports in an EtherChannel, apply configuration commands to the port-channel interface, for example, spanning-tree commands or commands to configure a Layer 2 EtherChannel as a trunk.

Port Aggregation Protocol

The Port Aggregation Protocol (PAgP) is a Cisco-proprietary protocol that can be run only on Cisco switches and on those switches licensed by vendors to support PAgP. PAgP facilitates the automatic creation of EtherChannels by exchanging PAgP packets between Ethernet interfaces.

By using PAgP, the switch learns the identity of partners capable of supporting PAgP and the capabilities of each interface. It then dynamically groups similarly configured interfaces into a single logical link (channel or aggregate port). Similarly configured interfaces are grouped based on hardware, administrative, and port parameter constraints. For example, PAgP groups the interfaces with the same speed, duplex mode, native VLAN, VLAN range, and trunking status and type. After grouping the links into an EtherChannel, PAgP adds the group to the spanning tree as a single switch port.

PAgP Modes

Table 26-1 shows the user-configurable EtherChannel PAgP modes for the channel-group interface configuration command.

Table 26-1 EtherChannel PAgP Modes 

Mode	Description
auto	Places an interface into a passive negotiating state, in which the interface responds to PAgP packets it receives but does not start PAgP packet negotiation. This setting minimizes the transmission of PAgP packets.
desirable	Places an interface into an active negotiating state, in which the interface starts negotiations with other interfaces by sending PAgP packets.
on	Forces the interface to channel without PAgP (or the Link Aggregation Control Protocol [LACP]). With the on mode, a usable EtherChannel exists only when an interface group in the on mode is connected to another interface group in the on mode.

Switch interfaces exchange PAgP packets only with partner interfaces configured in the auto or desirable modes. Interfaces configured in the on mode do not exchange PAgP packets.

Both the auto and desirable modes allow interfaces to negotiate with partner interfaces to determine if they can form an EtherChannel based on criteria such as interface speed and, for Layer 2 EtherChannels, trunking state and VLAN numbers.

Interfaces can form an EtherChannel when they are in different PAgP modes as long as the modes are compatible. For example:

•An interface in the desirable mode can form an EtherChannel with another interface that is in the desirable or auto mode.

•An interface in the auto mode can form an EtherChannel with another interface in the desirable mode.

An interface in the auto mode cannot form an EtherChannel with another interface that is also in the auto mode because neither interface starts PAgP negotiation.

An interface in the on mode that is added to a port channel is forced to have the same characteristics as the already existing on mode interfaces in the channel.

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Caution You should exercise care when setting the mode to on (manual configuration). All ports configured in the on mode are bundled in the same group and are forced to have similar characteristics. If the group is misconfigured, packet loss or spanning-tree loops might occur.

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If your switch is connected to a partner that is PAgP-capable, you can configure the switch interface for nonsilent operation by using the non-silent keyword. If you do not specify non-silent with the auto or desirable mode, silent mode is assumed.

Use the silent mode when the switch is connected to a device that is not PAgP-capable and seldom, if ever, sends packets. An example of a silent partner is a file server or a packet analyzer that is not generating traffic. In this case, running PAgP on a physical port connected to a silent partner prevents that switch port from ever becoming operational. However, the silent setting allows PAgP to operate, to attach the interface to a channel group, and to use the interface for transmission.

PAgP Interaction with Other Features

The Dynamic Trunking Protocol (DTP) and the Cisco Discovery Protocol (CDP) send and receive packets over the physical interfaces in the EtherChannel. Trunk ports send and receive PAgP protocol data units (PDUs) on the lowest numbered VLAN.

In Layer 2 EtherChannels, the first port in the channel that comes up provides its MAC address to the EtherChannel. If this port is removed from the bundle, one of the remaining ports in the bundle provides its MAC address to the EtherChannel.

PAgP sends and receives PAgP PDUs only from interfaces that are up and have PAgP enabled for the auto or desirable mode.

Link Aggregation Control Protocol

The LACP is defined in IEEE 802.3AD and enables Cisco switches to manage Ethernet channels between switches that conform to the 802.3AD protocol. LACP facilitates the automatic creation of EtherChannels by exchanging LACP packets between Ethernet interfaces.

By using LACP, the switch learns the identity of partners capable of supporting LACP and the capabilities of each interface. It then dynamically groups similarly configured interfaces into a single logical link (channel or aggregate port). Similarly configured interfaces are grouped based on hardware, administrative, and port parameter constraints. For example, LACP groups the interfaces with the same speed, duplex mode, native VLAN, VLAN range, and trunking status and type. After grouping the links into an EtherChannel, LACP adds the group to the spanning tree as a single switch port.

LACP Modes

Table 26-2 shows the user-configurable EtherChannel LACP modes for the channel-group interface configuration command.

Table 26-2 EtherChannel LACP Modes 

Mode	Description
active	Places an interface into an active negotiating state in which the interface starts negotiations with other interfaces by sending LACP packets.
passive	Places an interface into a passive negotiating state in which the interface responds to LACP packets that it receives, but does not start LACP packet negotiation. This setting minimizes the transmission of LACP packets.
on	Forces the interface to channel without PAgP or LACP. With the on mode, a usable EtherChannel exists only when an interface group in the on mode is connected to another interface group in the on mode.

Both the active and passive LACP modes enable interfaces to negotiate with partner interfaces to determine if they can form an EtherChannel based on criteria such as interface speed and, for Layer 2 EtherChannels, trunking state and VLAN numbers.

Interfaces can form an EtherChannel when they are in different LACP modes as long as the modes are compatible. For example:

•An interface in the active mode can form an EtherChannel with another interface that is in the active or passive mode.

•An interface in the passive mode cannot form an EtherChannel with another interface that is also in the passive mode because neither interface starts LACP negotiation.

LACP Interaction with Other Features

The DTP and the CDP send and receive packets over the physical interfaces in the EtherChannel. Trunk ports send and receive LACP PDUs on the lowest numbered VLAN.

In Layer 2 EtherChannels, the first port in the channel that comes up provides its MAC address to the EtherChannel. If this port is removed from the bundle, one of the remaining ports in the bundle provides its MAC address to the EtherChannel.

LACP sends and receives LACP PDUs only from interfaces that are up and have LACP enabled for the active or passive mode.

Load Balancing and Forwarding Methods

EtherChannel balances the traffic load across the links in a channel 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. EtherChannel load balancing can use MAC addresses or IP addresses, source or destination addresses, or both source and destination addresses. The selected mode applies to all EtherChannels configured on the switch. You configure the load balancing and forwarding method by using the port-channel load-balance global configuration command.

With source-MAC address forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the channel based on the source-MAC address of the incoming packet. Therefore, to provide load balancing, packets from different hosts use different ports in the channel, but packets from the same host use the same port in the channel.

With destination-MAC address forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the channel based on the destination host's MAC address of the incoming packet. Therefore, packets to the same destination are forwarded over the same port, and packets to a different destination are sent on a different port in the channel.

With source-and-destination MAC address forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the channel based on both the source and destination MAC addresses. This forwarding method, a combination source-MAC and destination-MAC address forwarding methods of load distribution, can be used if it is not clear whether source-MAC or destination-MAC address forwarding is better suited on a particular switch. With source-and-destination MAC-address forwarding, packets sent from host A to host B, host A to host C, and host C to host B could all use different ports in the channel.

With source-IP address-based forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the EtherChannel based on the source-IP address of the incoming packet. Therefore, to provide load-balancing, packets from different IP addresses use different ports in the channel, but packets from the same IP address use the same port in the channel.

With destination-IP address-based forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the EtherChannel based on the destination-IP address of the incoming packet. Therefore, to provide load-balancing, packets from the same IP source address sent to different IP destination addresses could be sent on different ports in the channel. But packets sent from different source IP addresses to the same destination IP address are always sent on the same port in the channel.

With source-and-destination IP address-based forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the EtherChannel based on both the source and destination IP addresses of the incoming packet. This forwarding method, a combination of source-IP and destination-IP address-based forwarding, can be used if it is not clear whether source-IP or destination-IP address-based forwarding is better suited on a particular switch. In this method, packets sent from the IP address A to IP address B, from IP address A to IP address C, and from IP address C to IP address B could all use different ports in the channel.

Different load-balancing methods have different advantages, and the choice of a particular load-balancing method should be based on the position of the switch in the network and the kind of traffic that needs to be load-distributed. In Figure 26-3, an EtherChannel of four workstations communicates with a router. Because the router is a single-MAC-address device, source-based forwarding on the switch EtherChannel ensures that the switch uses all available bandwidth to the router. The router is configured for destination-based forwarding because the large number of workstations ensures that the traffic is evenly distributed from the router EtherChannel.

Use the option that provides the greatest variety in your configuration. For example, if the traffic on a channel is going only to a single MAC address, using the destination-MAC address always chooses the same link in the channel. Using source addresses or IP addresses might result in better load balancing.

Figure 26-3 Load Distribution and Forwarding Methods

Configuring EtherChannels

These sections describe how to configure EtherChannel on Layer 2 interfaces:

•Default EtherChannel Configuration

•EtherChannel Configuration Guidelines

•Configuring Layer 2 EtherChannels (required)

•Configuring EtherChannel Load Balancing (optional)

•Configuring the PAgP Learn Method and Priority (optional)

•Configuring LACP Hot-Standby Ports (optional)

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Note Make sure that the interfaces are correctly configured. For more information, see the "EtherChannel Configuration Guidelines" section.

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Note After you configure an EtherChannel, configuration changes applied to the port-channel interface apply to all the physical interfaces assigned to the port-channel interface, and configuration changes applied to the physical interface affect only the interface where you apply the configuration.

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Default EtherChannel Configuration

Table 26-3 shows the default EtherChannel configuration.

Table 26-3 Default EtherChannel Configuration 

Feature	Default Setting
Channel groups	None assigned.
Port-channel logical interface	None defined.
PAgP mode	No default.
PAgP learn method	Aggregate-port learning on all interfaces.
PAgP priority	128 on all interfaces.
LACP mode	No default.
LACP learn method	Aggregate-port learning on all interfaces.
LACP port priority	32768 on all interfaces.
LACP system priority	32768.
LACP system ID	LACP system priority and the switch MAC address.
Load balancing	Load distribution on the switch is based on the source-MAC address of the incoming packet.

EtherChannel Configuration Guidelines

If improperly configured, some EtherChannel interfaces are automatically disabled to avoid network loops and other problems. Follow these guidelines to avoid configuration problems:

•More than 12 EtherChannels cannot be configured on a Catalyst 2970 switch.

•Configure a PAgP EtherChannel with up to eight Ethernet interfaces of the same type.

•Configure a LACP EtherChannel with up to 16 Ethernet interfaces of the same type. Up to eight ports can be active, and up to eight ports can be in standby mode.

•Configure all interfaces in an EtherChannel to operate at the same speeds and duplex modes.

•Enable all interfaces in an EtherChannel. An interface in an EtherChannel that is disabled by using the shutdown interface configuration command is treated as a link failure, and its traffic is transferred to one of the remaining interfaces in the EtherChannel.

•When a group is first created, all ports follow the parameters set for the first port to be added to the group. If you change the configuration of one of these parameters, you must also make the changes to all ports in the group:

–Allowed-VLAN list

–Spanning-tree path cost for each VLAN

–Spanning-tree port priority for each VLAN

–Spanning-tree Port Fast setting

•Do not configure a port to be a member of more than one EtherChannel group.

•Do not configure an EtherChannel in both the PAgP and LACP modes. EtherChannel groups running PAgP and LACP can coexist on the same switch. Individual EtherChannel groups can run either PAgP or LACP, but they cannot interoperate.

•Do not configure a Switched Port Analyzer (SPAN) destination as part of an EtherChannel.

•Do not configure a secure port as part of an EtherChannel or the reverse.

•Do not configure a port that is an active member of an EtherChannel as an 802.1X port. If 802.1X is enabled on a not-yet active port of an EtherChannel, the port does not join the EtherChannel.

•For Layer 2 EtherChannels:

–Assign all interfaces in the EtherChannel to the same VLAN, or configure them as trunks. Interfaces with different native VLANs cannot form an EtherChannel.

–If you configure an EtherChannel from trunk interfaces, verify that the trunking mode (ISL or 802.1Q) is the same on all the trunks. Inconsistent trunk modes on EtherChannel interfaces can have unexpected results.

–An EtherChannel supports the same allowed range of VLANs on all the interfaces in a trunking Layer 2 EtherChannel. If the allowed range of VLANs is not the same, the interfaces do not form an EtherChannel even when PAgP is set to the auto or desirable mode.

–Interfaces with different spanning-tree path costs can form an EtherChannel if they are otherwise compatibly configured. Setting different spanning-tree path costs does not, by itself, make interfaces incompatible for the formation of an EtherChannel.

Configuring Layer 2 EtherChannels

You configure Layer 2 EtherChannels by assigning interfaces to a channel group with the channel-group interface configuration command. This command automatically creates the port-channel logical interface.

Beginning in privileged EXEC mode, follow these steps to assign a Layer 2 Ethernet interface to a Layer 2 EtherChannel. This procedure is required.

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface interface-id	Enter interface configuration mode, and specify a physical interface to configure. Valid interfaces include physical interfaces. For a PAgP EtherChannel, you can configure up to eight interfaces of the same type and speed for the same group. For a LACP EtherChannel, you can configure up to 16 Ethernet interfaces of the same type. Up to eight ports can be active, and up to eight ports can be in standby mode.
Step 3	switchport mode {access | trunk} switchport access vlan vlan-id	Assign all interfaces as static-access ports in the same VLAN, or configure them as trunks. If you configure the interface as a static-access port, assign it to only one VLAN. The range is 1 to 4094.
Step 4	channel-group channel-group-number mode {auto [non-silent] | desirable [non-silent] | on} | {active | passive}	Assign the interface to a channel group, and specify the PAgP or the LACP mode. For channel-group-number, the range is 1 to 12. For mode, select one of these keywords: •auto—Enables PAgP only if a PAgP device is detected. It places an interface into a passive negotiating state, in which the interface responds to PAgP packets it receives but does not start PAgP packet negotiation. •desirable—Unconditionally enables PAgP. It places an interface into an active negotiating state, in which the interface starts negotiations with other interfaces by sending PAgP packets. •on—Forces the interface to channel without PAgP or LACP. With the on mode, a usable EtherChannel exists only when an interface group in the on mode is connected to another interface group in the on mode. •non-silent—(Optional) If your switch is connected to a partner that is PAgP-capable, configure the switch interface for nonsilent operation when the interface is in the auto or desirable mode. If you do not specify non-silent, silent is assumed. The silent setting is for connections to file servers or packet analyzers. This setting allows PAgP to operate, to attach the interface to a channel group, and to use the interface for transmission. •active—Enables LACP only if a LACP device is detected. It places an interface into an active negotiating state in which the interface starts negotiations with other interfaces by sending LACP packets. •passive—Enables LACP on an interface and places it into a passive negotiating state in which the interface responds to LACP packets that it receives, but does not start LACP packet negotiation. For information on compatible modes for the switch and its partner, see the "PAgP Modes" section and the "LACP Modes" section.
Step 5	end	Return to privileged EXEC mode.
Step 6	show running-config	Verify your entries.
Step 7	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To remove an interface from the EtherChannel group, use the no channel-group interface configuration command.

This example shows how to configure an EtherChannel. It assigns Gigabit Ethernet interfaces 0/4 and 0/5 as static-access ports in VLAN 10 to channel 5 with the PAgP mode desirable:

Switch# configure terminal 

Switch(config)# interface range gigabitethernet0/4 -5 

Switch(config-if-range)# switchport mode access

Switch(config-if-range)# switchport access vlan 10

Switch(config-if-range)# channel-group 5 mode desirable non-silent

Switch(config-if-range)# end 

This example shows how to configure an EtherChannel. It assigns Gigabit Ethernet interfaces 0/4 and 0/5 as static-access ports in VLAN 10 to channel 5 with the LACP mode active:

Switch# configure terminal 

Switch(config)# interface range gigabitethernet0/4 -5 

Switch(config-if-range)# switchport mode access

Switch(config-if-range)# switchport access vlan 10

Switch(config-if-range)# channel-group 5 mode active

Switch(config-if-range)# end 

Configuring EtherChannel Load Balancing

This section describes how to configure EtherChannel load balancing by using source-based or destination-based forwarding methods. For more information, see the "Load Balancing and Forwarding Methods" section.

Beginning in privileged EXEC mode, follow these steps to configure EtherChannel load balancing. This procedure is optional.

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	port-channel load-balance {dst-ip | dst-mac | src-dst-ip | src-dst-mac | src-ip | src-mac}	Configure an EtherChannel load-balancing method. The default is src-mac. Select one of these keywords to determine the load-distribution method: •dst-ip—Load distribution is based on the destination-host IP address. •dst-mac—Load distribution is based on the destination-host MAC address of the incoming packet. •src-dst-ip—Load distribution is based on the source-and-destination host-IP address. •src-dst-mac—Load distribution is based on the source-and-destination host-MAC address. •src-ip—Load distribution is based on the source-host IP address. •src-mac—Load distribution is based on the source-MAC address of the incoming packet.
Step 3	end	Return to privileged EXEC mode.
Step 4	show etherchannel load-balance	Verify your entries.
Step 5	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To return EtherChannel load balancing to the default configuration, use the no port-channel load-balance global configuration command.

Configuring the PAgP Learn Method and Priority

Network devices are classified as PAgP physical learners or aggregate-port learners. A device is a physical learner if it learns addresses by physical ports and directs transmissions based on that knowledge. A device is an aggregate-port learner if it learns addresses by aggregate (logical) ports. The learn method must be configured the same at both ends of the link.

When a device and its partner are both aggregate-port learners, they learn the address on the logical port-channel. The device sends packets to the source by using any of the interfaces in the EtherChannel. With aggregate-port learning, it is not important on which physical port the packet arrives.

PAgP cannot automatically detect when the partner device is a physical learner and when the local device is an aggregate-port learner. Therefore, you must manually set the learning method on the local device to learn addresses by physical ports. You also must set the load-distribution method to source-based distribution, so that any given source MAC address is always sent on the same physical port.

You also can configure a single interface within the group for all transmissions and use other interfaces for hot standby. The unused interfaces in the group can be swapped into operation in just a few seconds if the selected single interface loses hardware-signal detection. You can configure which interface is always selected for packet transmission by changing its priority with the pagp port-priority interface configuration command. The higher the priority, the more likely that the port will be selected.

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Note The Catalyst 2970 switch supports address learning only on aggregate ports even though the physical-port keyword is provided in the CLI. The pagp learn-method command and the pagp port-priority command have no effect on the switch hardware, but they are required for PAgP interoperability with devices that only support address learning by physical ports, such as the Catalyst 1900 switch.

When the link partner to the Catalyst 2970 switch is a physical learner (such as a Catalyst 1900 series switch), we recommend that you configure the Catalyst 2970 switch as a physical-port learner by using the pagp learn-method physical-port interface configuration command. Set the load-distribution method based on the source MAC address by using the port-channel load-balance src-mac global configuration command. The switch then sends packets to the Catalyst 1900 switch using the same interface in the EtherChannel from which it learned the source address. Use the pagp learn-method command only in this situation.

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Beginning in privileged EXEC mode, follow these steps to configure your switch as a PAgP physical-port learner and to adjust the priority so that the same port in the bundle is selected for sending packets. This procedure is optional.

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface interface-id	Enter interface configuration mode, and specify the interface for transmission.
Step 3	pagp learn-method physical-port	Select the PAgP learning method. By default, aggregation-port learning is selected, which means the switch sends packets to the source by using any of the interfaces in the EtherChannel. With aggregate-port learning, it is not important on which physical port the packet arrives. Select physical-port to connect with another switch that is a physical learner. Make sure to configure the port-channel load-balance global configuration command to src-mac as described in the "Configuring EtherChannel Load Balancing" section. The learning method must be configured the same at both ends of the link.
Step 4	pagp port-priority priority	Assign a priority so that the selected interface is chosen for packet transmission. For priority, the range is 0 to 255. The default is 128. The higher the priority, the more likely that the interface will be used for PAgP transmission.
Step 5	end	Return to privileged EXEC mode.
Step 6	show running-config or show pagp channel-group-number internal	Verify your entries.
Step 7	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To return the priority to its default setting, use the no pagp port-priority interface configuration command. To return the learning method to its default setting, use the no pagp learn-method interface configuration command.

Configuring LACP Hot-Standby Ports

When enabled, LACP tries to configure the maximum number of LACP-compatible ports in a channel, up to a maximum of 16 ports. Only eight LACP links can be active at one time. The software places any additional links in a hot-standby mode. If one of the active links becomes inactive, a link that is in the hot-standby mode becomes active in its place.

If you configure more than eight links for an EtherChannel group, the software automatically determines which of the hot-standby ports to make active based on the LACP priority. The software assigns to every link between systems that operate LACP a unique priority made up of these elements (in priority order):

•LACP system priority

•System ID (a combination of the LACP system priority and the switch MAC address)

•LACP port priority

•Port number

In priority comparisons, numerically lower values have higher priority. The priority determines which ports should be put in standby mode when there is a hardware limitation that prevents all compatible ports from aggregating.

Ports are considered for active use in aggregation in link-priority order starting with the port attached to the highest priority link. Each port is selected for active use if the preceding higher priority selections can also be maintained. Otherwise, the port is selected for standby mode.

You can change the default values of the LACP system priority and the LACP port priority to affect how the software selects active and standby links. For more information, see the "Configuring the LACP System Priority" section and the "Configuring the LACP Port Priority" section.

Configuring the LACP System Priority

You can configure the system priority for all of the EtherChannels that are enabled for LACP by using the lacp system-priority global configuration command. You cannot configure a system priority for each LACP-configured channel. By changing this value from the default, you can affect how the software selects active and standby links.

You can use the show etherchannel summary privileged EXEC command to see which ports are in the hot-standby mode (denoted with an H port-state flag).

Beginning in privileged EXEC mode, follow these steps to configure the LACP system priority. This procedure is optional.

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	lacp system-priority priority	Configure the LACP system priority. For priority, the range is 1 to 65535. The default is 32768. The lower the value, the higher the system priority.
Step 3	end	Return to privileged EXEC mode.
Step 4	show running-config or show lacp sys-id	Verify your entries.
Step 5	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To return the LACP system priority to the default value, use the no lacp system-priority global configuration command.

Configuring the LACP Port Priority

By default, all ports use the same port priority. If the local system has a lower value for the system priority and the system ID than the remote system, you can affect which of the hot-standby links become active first by changing the port priority of LACP EtherChannel ports to a lower value than the default. The hot-standby ports that have lower port numbers become active in the channel first. You can use the show etherchannel summary privileged EXEC command to see which ports are in the hot-standby mode (denoted with an H port-state flag).

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Note If LACP is not able to aggregate all the ports that are compatible (for example, the remote system might have more restrictive hardware limitations), all the ports that cannot be actively included in the EtherChannel are put in the hot-standby state and are used only if one of the channeled ports fails.

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Beginning in privileged EXEC mode, follow these steps to configure the LACP port priority. This procedure is optional.

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface interface-id	Enter interface configuration mode, and specify the interface to be configured.
Step 3	lacp port-priority priority	Configure the LACP port priority. For priority, the range is 1 to 65535. The is 32768. The lower the value, the more likely that the interface will be used for LACP transmission.
Step 4	end	Return to privileged EXEC mode.
Step 5	show running-config or show lacp [channel-group-number] internal	Verify your entries.
Step 6	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To return the LACP port priority to the default value, use the no lacp port-priority interface configuration command.

Displaying EtherChannel, PAgP, and LACP Status

To display EtherChannel, PAgP, and LACP status information, use the privileged EXEC commands described in Table 26-4:

Table 26-4 Commands for Displaying EtherChannel, PAgP, and LACP Status 

Command	Description
show etherchannel [channel-group-number {detail | port | port-channel | protocol | summary}] {detail | load-balance | port | port-channel | protocol | summary}	Displays EtherChannel information in a brief, detailed, and one-line summary form. Also displays the load-balance or frame-distribution scheme, port, port-channel, and protocol information.
show pagp [channel-group-number] {counters | internal | neighbor}	Displays PAgP information such as traffic information, the internal PAgP configuration, and neighbor information.
show lacp [channel-group-number] {counters | internal | neighbor}	Displays LACP information such as traffic information, the internal LACP configuration, and neighbor information.

You can clear PAgP channel-group information and traffic counters by using the clear pagp {channel-group-number counters | counters} privileged EXEC command.

You can clear LACP channel-group information and traffic counters by using the clear lacp {channel-group-number counters | counters} privileged EXEC command.

For detailed information about the fields in the displays, refer to the command reference for this release.