Table of Contents

Configuring EtherChannel

This chapter describes how to configure EtherChannel for switch routers. This chapter includes the following sections:

About EtherChannel

EtherChannel is a trunking technology that groups together multiple full-duplex 802.3 Ethernet interfaces to provide fault-tolerant, high-speed links between switches, routers, and servers. EtherChannel is a logical aggregation of multiple Ethernet interfaces. EtherChannel forms a single higher bandwidth routing or bridging endpoint. EtherChannel is designed primarily for host-to-switch connectivity or Inter-Switch Link (ISL) switch-to-switch connectivity (for example, connectivity to a Catalyst 5500 switch).

In summary, EtherChannel provides the following benefits:

The EtherChannel interface (consisting of up to four Ethernet interfaces) is treated as a single interface, which is called a port channel. You must configure EtherChannel on the EtherChannel interface rather than on the individual member Ethernet interfaces. You create the EtherChannel interface by using the interface port-channel interface configuration command. The switch router supports up to 64 port channels.

EtherChannel connections are fully compatible with Cisco IOS VLAN and routing technologies. The ISL VLAN trunking protocol can carry multiple VLANs across an EtherChannel, and routers attached to EtherChannel links can provide full multiprotocol routing with support for host standby using Host Standby Router Protocol (HSRP).

Your switch router supports Fast EtherChannel (FEC) and Gigabit EtherChannel (GEC).

Cisco Fast EtherChannel technology builds upon standards-based 802.3 full-duplex Fast Ethernet to provide a reliable high-speed solution for the campus network backbone. Fast EtherChannel provides bandwidth scalability within the campus by providing increments of 200 Mbps to 800 Mbps.

Cisco Gigabit EtherChannel technology provides bandwidth scalability within the campus by providing increments of 2 Gbps to 8 Gbps.

Note   For more detailed information about EtherChannel, refer to the "Configuring LAN Interfaces" chapter in the Cisco IOS Interface Configuration Guide .

Configuring EtherChannel Interfaces

This section describes how to configure Fast EtherChannel or Gigabit EtherChannel in Layer 3 switching. Configuring a Fast EtherChannel or a Gigabit EtherChannel consists of the following two-step process:

Step 2   Assign the Fast Ethernet or Gigabit Ethernet interfaces (up to four) to the port channel.

Note   When assigning interfaces to a specific port channel, the interfaces must be all Fast Ethernet, Gigabit Ethernet, or Enhanced Gigabit Ethernet. You cannot mix interface types within a single port-channel.

Creating the EtherChannel

To create an EtherChannel interface and assign its IP address and subnet mask, perform the following steps, beginning in global configuration mode:

Example

For a complete configuration example of Gigabit EtherChannel, see the "Catalyst 8540 CSR with ISL, VLAN, and BVI with GEC" section.

For more information on configuring EtherChannel, refer to the "Configuring LAN Interfaces" chapter in the Cisco IOS Interface Configuration Guide .

Assigning Interfaces to the EtherChannel

To assign Ethernet interfaces to the EtherChannel, perform the following steps, beginning in global configuration mode:

Caution   The EtherChannel interface is the routed interface. Do not enable Layer 3 addresses on the physical Fast Ethernet or Gigabit Ethernet interfaces. Do not assign bridge groups on the physical Fast Ethernet or Gigabit Ethernet interfaces because doing so creates loops. Finally, you must disable the Spanning Tree Protocol.

Example

For a complete configuration example of Gigabit EtherChannel, see the "Catalyst 8540 CSR with ISL, VLAN, and BVI with GEC" section.

For more information on configuring EtherChannel, refer to the "Configuring LAN Interfaces" chapter in the Cisco IOS Interface Configuration Guide .

Verifying the EtherChannel Configuration

To verify the EtherChannel configuration, use the following EXEC commands:

Example

The following examples shows the EtherChannel configuration:

Removing EtherChannel Interfaces

Disabling an EtherChannel and removing an interface from the EtherChannel consists of the following steps, described in the procedures below:

Step 2   Remove the Ethernet interfaces assigned to the EtherChannel.

To remove the network address from the EtherChannel, perform the following steps, beginning in global configuration mode:

Example

To remove Ethernet interfaces assigned to the EtherChannel, perform the following steps, beginning in global configuration mode:

Example

The Cisco IOS software automatically removes a Fast Ethernet or Gigabit Ethernet interface from the EtherChannel if the interface goes down, and the software automatically adds the interface to the EtherChannel when the interface is back up.

Currently, EtherChannel relies on keepalive signals to detect whether the line protocol is up or down. Keepalive signals are enabled by default on the Fast Ethernet and Gigabit Ethernet interfaces. If the line protocol on the interface goes down because it did not receive a keepalive signal, the EtherChannel detects that the line protocol is down and removes the interface from the EtherChannel.

However, if the line protocol remains up because keepalive signals are disabled on the Fast Ethernet or Gigabit Ethernet interface, the EtherChannel cannot detect this link failure (other than a cable disconnect) and does not remove the interface from the EtherChannel even if the line protocol goes down. This can result in unpredictable behavior.

About Port Aggregation Protocol

The Port Aggregation Protocol (PAgP) facilitates the automatic creation of Fast EtherChannel and Gigabit EtherChannel links by exchanging packets between channel-capable ports. The protocol learns the capabilities of port groups dynamically and informs the neighboring ports. Once PAgP identifies correctly paired channel-capable links, it groups the ports into a channel. PAgP enhances the port-channel functionality.

Enabling PAgP between a local and a remote device has the following benefits:

When PAgP is not enabled on an interface, port aggregation is handled manually through the MIB or by the command line interface, and the MIB remains static between manual changes.

A PAgP port state machine and a set of per-physical and per-port channel variables control the protocol. A physical port is associated with another physical port that has the same group capability. As long as the physical port is up, PAgP packets are periodically transmitted. If data packets (not PAgP packets) are received, the assumption is made that the port is connected to a non-PAgP capable device. If PAgP packets are received, it is established that the physical port has a bi-directional connection to another PAgP capable device. After a physical port receives two PAgP packets, the protocol aggregates the port to a port channel and the port assumes UPPAgP or S7 state. If the port stops receiving PAgP packets, it leaves the S7 state and is removed from the port channel.

Following are the three user-configurable channel modes: on, auto, and desirable. PAgP packets are exchanged only between ports in auto and desirable mode. Ports configured in on mode do not exchange PAgP packets. Table 10-1 describes each mode.

Both the auto and desirable modes allow ports to negotiate with connected ports to determine if they can form a channel, based on criteria such as port speed, trunking state, native VLAN, and so on. Ports can form an EtherChannel when they are in different channel modes as long as the modes are compatible. For example:

Configuring PAgP

To configure PAgP parameters on the EtherChannel, perform the following steps, beginning in global configuration mode:

	Command	Purpose
Step 1	Router(config)# interface interface-type slot/subslot/interface Router(config-if)#	Enters interface configuration mode to configure the interface you want to assign to the EtherChannel. You can assign any interface on any interface module installed on the system to the EtherChannel.
Step 2	Router(config-if)# no ip address	Disables the IP address. If the Fast Ethernet or Gigabit Ethernet interface already exists and has an IP address assigned, you must disable it before performing the next step. The Ethernet interface uses the IP address assigned to the EtherChannel interface.
Step 3	Router(config-if)# [no] channel-group channel-number mode auto | mode desirable | mode on	Assigns the Fast Ethernet or Gigabit Ethernet interfaces to the EtherChannel with the channel-group command. The channel number must be the same channel number you assigned to the EtherChannel interface. Configures PAgP parameters on the channel-group to automatically create FEC and GEC links. To issue the PAgP parameters issue, the mode command. The three configurable modes follow: auto enables PAgP only if a PAgP device is detected. desirable enables PAgP unconditionally on EtherChannel enabled ports. on forces the port to form a channel. For a detailed description of the command modes, see Table 10-1.
Step 4	Router(config-if)# exit Router(config)#	Exits interface configuration mode. Repeat Steps 3 through 6 to add up to four Fast Ethernet or Gigabit Ethernet interfaces to the Fast EtherChannel. Note    Up to four ports can be members of a port channel. The four ports need not operate in the same PAgP mode. It is only necessary that the two PAgP enabled peer ports have a valid PAgP mode combination. For instance, it would not make sense to have both peer ports configured for auto mode operation. Valid transmission mode combinations for peer ports are on-on, desirable-desirable, and auto-desirable.
Step 5	Router(config-if)# end Router#	Returns to privileged EXEC mode.
Step 6	Router# copy system:running-config nvram:startup-config	Saves your configuration changes to NVRAM.

Example

The following is an example of enabling PAgP on the EtherChannel by issuing the mode desirable command:

Verifying the PAgP Configuration

To verify the PAgP configuration on the EtherChannel, use the following EXEC commands:

Example

The following example shows the PAgP enabled port-channel member:

Example

The following example shows PAgP configuration between two Catalyst 8540s. Status information about the PAgP configuration is available by issuing the show pagp counters| internal | neighbor commands.

The port channel is configured and the first member interface is added. The show pagp counters output shows the PAgP status information before the peer interface has been added as a PAgP enabled member of the port-channel. Note that U4 is the transmission state of the interface and the S4 state shows that the port has been configured as a member of the aggregation port (port-channel) and that it has not yet received any PAgP packets.

The show pagp internal output shows the PAgP status information before the peer interface has been added as a PAgP enabled member of the port channel. The PAgP enabled interface is sending PAgP packets. Note that the partner count is 0.

The show pagp neighbor output shows that the peer interface has not been added as no partner name is indicated in the output.

After the peer interface has been added to the port channel, the show pagp internal and the show pagp neighbor outputs indicate that both members are exchanging PAgP packets. Note that the U4 and S4 transmission state is replaced with a U6 and S7 transmission state.

The U6 and S7 state indicates that the port is part of an aggregation port and PAgP packets are being sent and received on this port. In the U6 transmission state, PAgP hello packets are exchanged once every 30 seconds.

Note   The PAgP packet count displayed through the show pagp counters command can be reset to zero by using the clear pagp counters command. The clear pagp channel-number counters command selectively resets the PAgP packet counters of a particular port-channel. The clear pagp counters command clears the PAgP counters of all port-channels.

About Encapsulation over EtherChannel

When configuring encapsulation over FEC or GEC, be sure to configure the ISL or 802.1Q over the EtherChannel (that is, the port-channel interface), not its member ports. Also make sure that you do not apply protocol-level configuration (such as an IP address or a bridge group assignment) to the member interfaces. All protocol-level configuration should be on the port-channel or on its subinterface. You must configure ISL or 802.1Q encapsulation on the partner system of the EtherChannel as well.

Note   When configuring encapsulation on EtherChannel, you cannot configure both ISL and 802.1Q on the same EtherChannel interface.

Configuring Encapsulation over EtherChannel

To configure encapsulation on a subinterface over EtherChannel, perform the following steps, beginning in global configuration mode:

Example

The following example demonstrates configuring a subinterface and encapsulation over an EtherChannel:

For more information on configuring EtherChannel encapsulation, refer to the "Configuring LAN Interfaces" chapter in the Cisco IOS Interface Configuration Guide .

Monitoring the EtherChannel

Once Fast EtherChannel or Gigabit EtherChannel is configured, you can monitor its status using the following EXEC command:

Example

The following example shows how to monitor the EtherChannel operation:

For more information on this command, refer to the Cisco IOS Interface Command Reference publication.

Configuring the EtherChannel concludes the suggested process for configuring your switch router. You have the option of configuring system management tasks to monitor and fine tune your switch router's performance. For these tasks, refer to the Cisco IOS Configuration Fundamentals Configuration Guid e.