Catalyst 4500 Series Switch Cisco IOS Software Configuration Guide, 12.2(18)EW

Understanding and Configuring EtherChannel

This chapter describes how to use the command-line interface (CLI) to configure EtherChannel on the Catalyst 4500 series switch Layer 2 or Layer 3 interfaces. It also provides guidelines, procedures, and configuration examples.

This chapter includes the following major sections:

•Overview of EtherChannel

•EtherChannel Configuration Guidelines and Restrictions

•Configuring EtherChannel

Note The commands in the following sections can be used on all Ethernet interfaces on a Catalyst 4500 series switch, including the uplink ports on the supervisor engine.

Note For complete syntax and usage information for the switch commands used in this chapter, look at the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/hw/switches/ps4324/index.html

If the command is not found in the Catalyst 4500 Command Reference, it is located in the larger Cisco IOS library. Refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/ps6350/index.html

Overview of EtherChannel

These subsections describe how EtherChannel works:

•Understanding Port-Channel Interfaces

•Understanding How EtherChannels Are Configured

•Understanding Load Balancing

EtherChannel bundles individual Ethernet links into a single logical link that provides bandwidth up to 1600 Mbps (Fast EtherChannel full duplex) or 16 Gbps (Gigabit EtherChannel) between a Catalyst 4500 series switch and another switch or host.

A Catalyst 4500 series switch supports a maximum of 64 EtherChannels. You can form an EtherChannel with up to eight compatibly configured Ethernet interfaces across modules in a Catalyst 4500 series switch. All interfaces in each EtherChannel must be the same speed and must be configured as either Layer 2 or Layer 3 interfaces.

Note The network device to which a Catalyst 4500 series switch is connected may impose its own limits on the number of interfaces in an EtherChannel.

If a segment within an EtherChannel fails, traffic previously carried over the failed link switches to the remaining segments within the EtherChannel. Once the segment fails, an SNMP trap is sent, identifying the switch, the EtherChannel, and the failed link. Inbound broadcast and multicast packets on one segment in an EtherChannel are blocked from returning on any other segment of the EtherChannel.

Understanding Port-Channel Interfaces

Each EtherChannel has a numbered port-channel interface. A configuration applied to the port-channel interface affects all physical interfaces assigned to that interface.

Note QoS does not propagate to members. The defaults, QoS cos = 0 and QoS dscp = 0, apply on the port-channel. Input or output policies applied on individual interfaces will be ignored.

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 physical interfaces affects 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 (such commands can be STP commands or commands to configure a Layer 2 EtherChannel as a trunk).

Understanding How EtherChannels Are Configured

These subsections describe how EtherChannels are configured:

•EtherChannel Configuration Overview

•Understanding Manual EtherChannel Configuration

•Understanding PAgP EtherChannel Configuration

•Understanding IEEE 802.3ad LACP EtherChannel Configuration

EtherChannel Configuration Overview

You can configure EtherChannels manually or you can use the Port Aggregation Control Protocol (PAgP) or, with Release Cisco IOS Release 12.1(20)EW and later, 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. PAgP is a Cisco-proprietary protocol and LACP is defined in IEEE 802.3ad.

PAgP and LACP do not interoperate with each other. Ports configured to use PAgP cannot form EtherChannels with ports configured to use LACP and vice versa.

Table 18-1 lists the user-configurable EtherChannel modes.

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 PAgP EtherChannel Configuration

PAgP supports the automatic creation of EtherChannels by exchanging PAgP packets between LAN ports. PAgP packets are exchanged only between ports in auto and desirable modes.

The protocol learns the capabilities of LAN port groups dynamically and informs the other LAN ports. Once PAgP 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.

Both the auto and desirable modes allow PAgP to negotiate between LAN ports to determine if they can form an EtherChannel, based on criteria such as port speed and trunking state. Layer 2 EtherChannels also use VLAN numbers.

LAN ports can form an EtherChannel when they are in different PAgP modes if the modes are compatible. For example:

•A LAN port in desirable mode can form an EtherChannel successfully with another LAN port that is in desirable mode.

•A LAN port in desirable mode can form an EtherChannel with another LAN port in auto mode.

•A LAN port in auto mode cannot form an EtherChannel with another LAN port that is also in auto mode, because neither port will initiate negotiation.

Understanding IEEE 802.3ad LACP EtherChannel Configuration

Release Cisco IOS Release 12.1(20)EW and later releases support IEEE 802.3ad LACP EtherChannels. 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.

Both the passive and active modes allow LACP to negotiate between LAN ports to determine if they can form an EtherChannel, based on criteria such as port speed and trunking state. Layer 2 EtherChannels also use VLAN numbers.

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

•A LAN port in active mode can form an EtherChannel successfully with another LAN port that is in active mode.

•A LAN port in active mode can form an EtherChannel with another LAN port in passive mode.

•A LAN port in passive mode cannot form an EtherChannel with another LAN port that is also in passive mode, because neither port will initiate negotiation.

LACP uses the following parameters:

•LACP system priority—You may 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. 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 Layer 2 EtherChannels" section. LACP uses the port priority with the port number to form the port identifier.

Note Standby and "sub-channeling" are not supported in LACP and PagP.

•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

LACP tries to configure the maximum number of compatible ports in an EtherChannel, up to the maximum allowed by the hardware (eight ports). If a port can not be actively included in a channel, it will not be included automatically if a channelled port fails.

Understanding Load Balancing

EtherChannel can balance the traffic load across the links in the channel. It does this by reducing part of the binary pattern formed from the addresses or ports in the frame to a numerical value that selects one of the links in the channel. To balance the load, EtherChannel uses MAC addresses, IP addresses, or Layer 4 port numbers, and either the message source or message destination, or both.

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.

Note Load balancing can only be configured globally. As a result, all channels (manually configured, PagP, or LACP) will use the same load balancing method.

For additional information on load balancing, see the "Configuring EtherChannel Load Balancing" section.

EtherChannel Configuration Guidelines and Restrictions

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

•All Ethernet interfaces on all modules support EtherChannel (maximum of eight interfaces) with no requirement that interfaces be physically contiguous or on the same module.

•Configure all interfaces in an EtherChannel to operate at the same speed and duplex mode.

•Enable all interfaces in an EtherChannel. If you shut down an interface in an EtherChannel, it is treated as a link failure and its traffic is transferred to one of the remaining interfaces in the EtherChannel.

•An EtherChannel will not form if one of the interfaces is a Switched Port Analyzer (SPAN) destination port.

•For Layer 3 EtherChannels:

–Assign Layer 3 addresses to the port-channel logical interface, not to the physical interfaces in the channel.

•For Layer 2 EtherChannels:

–Assign all interfaces in the EtherChannel to the same VLAN, or configure them as trunks.

–If you configure an EtherChannel from trunk interfaces, verify that the trunking mode is the same on all the trunks. Interfaces in an EtherChannel with different trunk modes 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.

–Interfaces with different Spanning Tree Protocol (STP) port path costs can form an EtherChannel as long they are otherwise compatibly configured. Setting different STP port path costs does not, by itself, make interfaces incompatible for the formation of an EtherChannel.

•After you configure an EtherChannel, any configuration that you apply to the port-channel interface affects the EtherChannel; any configuration that you apply to the physical interfaces affects only the interface where you apply the configuration.

•You cannot configure a 802.1x port in an EtherChannel.

Configuring EtherChannel

These sections describe how to configure EtherChannel:

•Configuring Layer 3 EtherChannels

•Configuring Layer 2 EtherChannels

•Configuring the LACP System Priority and System ID

•Configuring EtherChannel Load Balancing

•Removing an Interface from an EtherChannel

•Removing an EtherChannel

Note Ensure that the interfaces are configured correctly (see the "EtherChannel Configuration Guidelines and Restrictions" section).

Configuring Layer 3 EtherChannels

To configure Layer 3 EtherChannels, create the port-channel logical interface and then put the Ethernet interfaces into the port-channel.

These sections describe Layer 3 EtherChannel configuration:

•Creating Port-Channel Logical Interfaces

•Configuring Physical Interfaces as Layer 3 EtherChannels

Creating Port-Channel Logical Interfaces

Note To move an IP address from a physical interface to an EtherChannel, you must delete the IP address from the physical interface before configuring it on the port-channel interface.

To create a port-channel interface for a Layer 3 EtherChannel, perform this task:

Switch(config)# interface port-channel 
port_channel_number 

Switch(config-if)# ip address ip_address mask 

Switch(config-if)# end 

Switch# show running-config interface 
port-channel port_channel_number 

This example shows how to create port-channel interface 1:

Switch# configure terminal 

Switch(config)# interface port-channel 1 

Switch(config-if)# ip address 172.32.52.10 255.255.255.0 

Switch(config-if)# end 

This example shows how to verify the configuration of port-channel interface 1:

Switch# show running-config interface port-channel 1 

Building configuration...

Current configuration:

!

interface Port-channel1

 ip address 172.32.52.10 255.255.255.0

 no ip directed-broadcast

end

Switch#

Configuring Physical Interfaces as Layer 3 EtherChannels

To configure physical interfaces as Layer 3 EtherChannels, perform this task for each interface:

Switch(config)# interface {fastethernet | 
gigabitethernet} slot/port 

Switch(config-if)# no switchport

Switch(config-if)# no ip address 

Switch(config-if)# channel-group port_channel_number 
mode {active | on | auto | passive | desirable} 

Switch(config-if)# end 

Switch# show running-config interface port-channel 
port_channel_number 

Switch# show running-config interface {fastethernet 
| gigabitethernet} slot/port 

Switch# show interfaces {fastethernet | 
gigabitethernet} slot/port etherchannel 

Switch# show etherchannel 1 port-channel 

This example shows how to configure Fast Ethernet interfaces 5/4 and 5/5 into port-channel 1 with PAgP mode desirable:

Switch# configure terminal 

Switch(config)# interface range fastethernet 5/4 - 5 (Note: Space is mandatory.)

Switch(config-if)# no switchport 

Switch(config-if)# no ip address 

Switch(config-if)# channel-group 1 mode desirable 

Switch(config-if)# end 

Note See the "Configuring a Range of Interfaces" section on page 4-4 for information about the range keyword.

The following two examples shows how to verify the configuration of Fast Ethernet interface 5/4:

Switch# show running-config interface fastethernet 5/4 

Building configuration...

Current configuration:

!

interface FastEthernet5/4

 no ip address

 no switchport

 no ip directed-broadcast

 channel-group 1 mode desirable

end

Switch# show interfaces fastethernet 5/4 etherchannel 

Port state    = EC-Enbld Up In-Bndl Usr-Config

Channel group = 1           Mode = Desirable     Gcchange = 0

Port-channel  = Po1         GC   = 0x00010001    Pseudo-port-channel = Po1

Port indx     = 0           Load = 0x55

Flags:  S - Device is sending Slow hello.  C - Device is in Consistent state.

        A - Device is in Auto mode.        P - Device learns on physical port.

Timers: H - Hello timer is running.        Q - Quit timer is running.

        S - Switching timer is running.    I - Interface timer is running.

Local information:

                                Hello    Partner  PAgP     Learning  Group

Port      Flags State   Timers  Interval Count   Priority   Method  Ifindex

Fa5/4     SC    U6/S7           30s      1        128        Any      55

Partner's information:

          Partner              Partner          Partner         Partner Group

Port      Name                 Device ID        Port       Age  Flags   Cap.

Fa5/4     JAB031301            0050.0f10.230c   2/45         1s SAC     2D

Age of the port in the current state: 00h:54m:52s

Switch# 

This example shows how to verify the configuration of port-channel interface 1 after the interfaces have been configured:

Switch# show etherchannel 1 port-channel 

                Channel-group listing:

                ----------------------

Group: 1

------------

                Port-channels in the group:

                ----------------------

Port-channel: Po1

------------

Age of the Port-channel   = 01h:56m:20s

Logical slot/port   = 10/1           Number of ports = 2

GC                  = 0x00010001      HotStandBy port = null

Port state          = Port-channel L3-Ag Ag-Inuse

Ports in the Port-channel:

Index   Load   Port

-------------------

  1     00      Fa5/6

  0     00      Fa5/7

Time since last port bundled:    00h:23m:33s    Fa5/6

Switch#

Configuring Layer 2 EtherChannels

To configure Layer 2 EtherChannels, configure the Ethernet interfaces with the channel-group command. This creates the port-channel logical interface.

Note Cisco IOS software creates port-channel interfaces for Layer 2 EtherChannels when you configure Layer 2 Ethernet interfaces with the channel-group command.

To configure Layer 2 Ethernet interfaces as Layer 2 EtherChannels, perform this task for each interface:

Switch(config)# interface {fastethernet | gigabitethernet} 
slot/port 

Switch(config-if)# channel-group port_channel_number mode 
{active | on | auto | passive | desirable} 

Switch(config-if)# end 

Switch# show running-config interface {fastethernet | 
gigabitethernet} slot/port 

Switch# show interface {fastethernet | gigabitethernet} 
slot/port etherchannel 

This example shows how to configure Fast Ethernet interfaces 5/6 and 5/7 into port-channel 2 with PAgP mode desirable:

Switch# configure terminal 

Switch(config)# interface range fastethernet 5/6 - 7 (Note: Space is mandatory.)

Switch(config-if-range)# channel-group 2 mode desirable 

Switch(config-if-range)# end 

Note See the "Configuring a Range of Interfaces" section on page 4-4 for information about the range keyword.

This example shows how to verify the configuration of port-channel interface 2:

Switch# show running-config interface port-channel 2 

Building configuration...

Current configuration:

!

interface Port-channel2

 switchport access vlan 10

 switchport mode access

end

Switch# 

The following two examples show how to verify the configuration of Fast Ethernet interface 5/6:

Switch# show running-config interface fastethernet 5/6 

Building configuration...

Current configuration:

!

interface FastEthernet5/6

 switchport access vlan 10

 switchport mode access

 channel-group 2 mode desirable

end

Switch# show interfaces fastethernet 5/6 etherchannel 

Port state    = EC-Enbld Up In-Bndl Usr-Config

Channel group = 1           Mode = Desirable     Gcchange = 0

Port-channel  = Po1         GC   = 0x00010001 

Port indx     = 0           Load = 0x55

Flags:  S - Device is sending Slow hello.  C - Device is in Consistent state.

        A - Device is in Auto mode.        P - Device learns on physical port.

        d - PAgP is down.

Timers: H - Hello timer is running.        Q - Quit timer is running.

        S - Switching timer is running.    I - Interface timer is running.

Local information:

                                Hello    Partner  PAgP     Learning  Group

Port      Flags State   Timers  Interval Count   Priority   Method  Ifindex

Fa5/6     SC    U6/S7           30s      1        128        Any      56

Partner's information:

          Partner              Partner          Partner         Partner Group

Port      Name                 Device ID        Port       Age  Flags   Cap.

Fa5/6     JAB031301            0050.0f10.230c   2/47        18s SAC     2F

Age of the port in the current state: 00h:10m:57s

This example shows how to verify the configuration of port-channel interface 2 after the interfaces have been configured:

Switch# show etherchannel 2 port-channel 

                Port-channels in the group:

                ----------------------

Port-channel: Po2

------------

Age of the Port-channel   = 00h:23m:33s

Logical slot/port   = 10/2           Number of ports in agport = 2

GC                  = 0x00020001      HotStandBy port = null

Port state          = Port-channel Ag-Inuse

Ports in the Port-channel:

Index   Load   Port

-------------------

  1     00      Fa5/6

  0     00      Fa5/7

Time since last port bundled:    00h:23m:33s    Fa5/6

Switch# 

Configuring the LACP System Priority and System ID

The LACP system ID is the combination of the LACP system priority value and the MAC address of the switch.

To configure the LACP system priority and system ID, perform this task:

Router(config)# lacp system-priority 
priority_value

Router(config)# no system port-priority 

Router(config)# end 

Router# show lacp sys-id 

This example shows how to configure the LACP system priority:

Switch# configure terminal 

Switch(config)# lacp system-priority 23456

Switch(config)# end 

Switch(config)# 

Switch>show module

Mod  Ports Card Type                              Model             Serial No.

----+-----+--------------------------------------+-----------------+-----------

 1      2  1000BaseX (GBIC) Supervisor(active)    WS-X4014          JAB063808YZ

 2     48  10/100BaseTX (RJ45)                    WS-X4148-RJ       JAB0447072W

 3     48  10/100BaseTX (RJ45)V                   WS-X4148-RJ45V    JAE061704J6

 4     48  10/100BaseTX (RJ45)V                   WS-X4148-RJ45V    JAE061704ML

 M MAC addresses                    Hw  Fw           Sw               Status

--+--------------------------------+---+------------+----------------+---------

 1 0005.9a39.7a80 to 0005.9a39.7a81 2.1 12.1(12r)EW  12.1(13)EW(0.26) Ok

 2 0002.fd80.f530 to 0002.fd80.f55f 0.1                               Ok

 3 0009.7c45.67c0 to 0009.7c45.67ef 1.6                               Ok

 4 0009.7c45.4a80 to 0009.7c45.4aaf 1.6                               Ok

This example shows how to verify the configuration:

Switch# show lacp sys-id 

23456,0050.3e8d.6400

Switch# 

The system priority is displayed first, followed by the MAC address of the switch.

Configuring EtherChannel Load Balancing

Note Load balancing can only be configured globally. As a result, all channels (manually configured, PagP, or LACP) will use the same load balancing method.

To configure EtherChannel load balancing, perform this task:

Switch(config)# [no] port-channel load-balance 
{src-mac | dst-mac | src-dst-mac | src-ip | 
dst-ip | src-dst-ip | src-port | dst-port | 
src-dst-port}

Switch(config)# end 

Switch# show etherchannel load-balance 

The load-balancing keywords are:

•src-mac—Source MAC addresses

•dst-mac—Destination MAC addresses

•src-dst-mac—Source and destination MAC addresses

•src-ip—Source IP addresses

•dst-ip—Destination IP addresses

•src-dst-ip—Source and destination IP addresses (Default)

•src-port—Source Layer 4 port

•dst-port—Destination Layer 4 port

•src-dst-port—Source and destination Layer 4 port

This example shows how to configure EtherChannel to use source and destination IP addresses:

Switch# configure terminal 

Switch(config)# port-channel load-balance dst-mac 

Switch(config)# end 

Switch(config)# 

This example shows how to verify the configuration:

Switch# show etherchannel load-balance 

Source XOR Destination IP address

Switch# 

Removing an Interface from an EtherChannel

To remove an Ethernet interface from an EtherChannel, perform this task:

Switch(config)# interface {fastethernet | 
gigabitethernet} slot/port 

Switch(config-if)# no channel-group 

Switch(config-if)# end 

Switch# show running-config interface 
{fastethernet | gigabitethernet} slot/port 

Switch# show interface {fastethernet | 
gigabitethernet} slot/port etherchannel 

This example shows how to remove Fast Ethernet interfaces 5/4 and 5/5 from port-channel 1:

Switch# configure terminal 

Switch(config)# interface range fastethernet 5/4 - 5 (Note: Space is mandatory.)

Switch(config-if)# no channel-group 1 

Switch(config-if)# end 

Removing an EtherChannel

If you remove an EtherChannel, the member ports are shut down and removed from the Channel group.

Note You must remove an EtherChannel before changing a port from Layer 2 to Layer 3, or Layer 3 to Layer 2.

To remove an EtherChannel, perform this task:

Switch(config)# no interface port-channel 
port_channel_number 

Switch(config)# end 

Switch# show etherchannel summary 

This example shows how to remove port-channel 1:

Switch# configure terminal 

Switch(config)# no interface port-channel 1 

Switch(config)# end