Catalyst 4500 Series Switch Cisco IOS Software Configuration Guide, 12.1E
Understanding and Configuring EtherChannel
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Table Of Contents

Understanding and Configuring EtherChannel

Overview of EtherChannel

Understanding Port-Channel Interfaces

Understanding the Port Aggregation Protocol

Understanding Load Balancing

EtherChannel Configuration Guidelines and Restrictions

Configuring EtherChannel

Configuring Layer 3 EtherChannels

Creating Port-Channel Logical Interfaces

Configuring Physical Interfaces as Layer 3 EtherChannels

Configuring Layer 2 EtherChannel

Configuring EtherChannel Load Balancing

Removing an Interface from an EtherChannel

Removing an EtherChannel


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, including the uplink ports on the supervisor engine.

Note For complete syntax and usage information for the switch commands used in this chapter, refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference and the publications at
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/index.htm

Overview of EtherChannel

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 and another switch or host.

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

Note The network device to which a Catalyst 4500 series 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.

The following sections describe how EtherChannel works:

•Understanding Port-Channel Interfaces

•Understanding the Port Aggregation Protocol

•Understanding Load Balancing

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.

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 the Port Aggregation Protocol

The Port Aggregation Protocol (PAgP) expedites the automatic creation of EtherChannels by exchanging packets between Ethernet interfaces. PAgP packets are exchanged only between interfaces in auto and desirable modes. Interfaces configured in the on mode do not exchange PAgP packets.

The protocol learns the capabilities of interface groups dynamically and informs the other interfaces. When PAgP identifies correctly matched Ethernet links, it groups the links into an EtherChannel. The EtherChannel is then added to the spanning tree as a single bridge port.

EtherChannel includes three user-configurable modes: on, auto, and desirable (see Table 15-1Table 15-1). Only auto and desirable are PAgP modes.

Table 15-1 EtherChannel Modes

Mode
Description

on

Mode that forces the interface to channel without PAgP. In 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.

auto

PAgP mode that places an interface in a passive negotiating state in which the interface responds to PAgP packets it receives but does not initiate PAgP negotiation.

desirable

PAgP mode that places an interface in an active negotiating state in which the interface initiates negotiations with other interfaces by sending PAgP packets.


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

Interfaces between two connected switches can form an EtherChannel when they are in different PAgP modes as long as the modes are compatible. This compatibility of the modes is shown in Table 15-2Table 15-2.

Table 15-2 Compatibility of EtherChannel Modes

 
desirable
auto
on
desirable

Yes

Yes

No

auto

Yes

No

No

on

No

No

Yes


Understanding Load Balancing

EtherChannel balances 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, IP addresses, or Layer 4 port numbers; either source or destination or both source and destination.

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 operates at the switch level rather than per-channel, applying globally for all channels on the switch.

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 even when set to the auto or desirable mode.

–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.

Configuring EtherChannel

These sections describe how to configure EtherChannel:

•Configuring Layer 3 EtherChannels

•Configuring Layer 2 EtherChannel

•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 procedure:

 
Task
Command

Step 1 

Create the port-channel interface. The value for port_channel_number can range from 1 to 64 

Switch(config)# interface port-channel 
port_channel_number

Step 2 

Assign an IP address and subnet mask to the EtherChannel. 

Switch(config-if)# ip address ip_address mask

Step 3 

Exit configuration mode. 

Switch(config-if)# end

Step 4 

Verify the configuration. 

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 procedure for each interface:

 
Task
Command

Step 1 

Select a physical interface to configure. 

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

Step 2 

Make this a Layer 3 routed port. 

Switch(config-if)# no switchport

Step 3 

Ensure that there is no IP address assigned to the physical interface. 

Switch(config-if)# no ip address

Step 4 

Configure the interface in a port-channel and specify the PAgP mode. 

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

Step 5 

Exit configuration mode. 

Switch(config-if)# end

Step 6 

Verify the configuration. 

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 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 EtherChannel

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

Note Cisco IOS 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 procedure for each interface:

 
Task
Command

Step 1 

Select a physical interface to configure. 

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

Step 2 

Configure the interface in a port-channel and specify the PAgP mode. 

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

Step 3 

Exit configuration mode. 

Switch(config-if)# end

Step 4 

Verify the configuration. 

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 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.

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 EtherChannel Load Balancing

Note Load balancing operates at the switch level rather than per-channel, applying globally for all channels on the switch.

To configure EtherChannel load balancing, perform this procedure:

 
Task
Command

Step 1 

Configure EtherChannel load balancing.

Use the no keyword to return EtherChannel load balancing to the default configuration. 

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}

Step 2 

Exit configuration mode. 

Switch(config)# end

Step 3 

Verify the configuration. 

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 src-dst-ip 

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 procedure:

 
Task
Command

Step 1 

Select a physical interface to configure. 

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

Step 2 

Remove the interface from the port-channel interface. 

Switch(config-if)# no channel-group

Step 3 

Exit configuration mode. 

Switch(config-if)# end

Step 4 

Verify the configuration. 

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.

To remove an EtherChannel, perform this procedure:

 
Task
Command

Step 1 

Remove the port-channel interface. 

Switch(config)# no interface port-channel 
port_channel_number

Step 2 

Exit configuration mode. 

Switch(config)# end

Step 3 

Verify the configuration. 

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