Configuring Layer 3 Ether Channels

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3550(config)# interface port-channel 2

3 55 0(config-if)# no switchport

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

© 2002, CiscoSystems, Inc. All rights reserved.

Cisco CCIE Prep v1.0—Module5-4

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

Use the steps outlined in the following table to create a port-channel interface for a Layer 3 EtherChannel:

Table 4-23: Layer 3 EtherChannel

Command

Purpose

3550(config)# interface portchannel port-channel-number

Enters interface configuration mode and creates the port-channel logical interface. For port-channel-number, the range is 1 to 64.

3550(config-if)# no switchport

Puts the interface into Layer 3 mode.

3550(config-if)# ip address ip-address mask

Assigns an IP address and subnet mask to the EtherChannel.

Note To remove the port-channel, use the no interface port-channel port-channel-number global configuration command.

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.

3550(config)# int faO/18

3550(config-if)# no switchport

3550(config-if)# no ip address

3550(config-if)# channel-group 2 mode auto

3550(config-if)# int faO/19

3550(config-if)# no switchport

3550(config-if)# no ip address

3550(config-if)# channel-group 2 mode auto

3550(config-if)# int faO/2O

3550(config-if)# no switchport

3550(config-if)# no ip address

3550(config-if)# channel-group 2 mode auto

3550(config-if)# int faO/19

3550(config-if)# no switchport

3550(config-if)# no ip address

3550(config-if)# channel-group 2 mode auto

3550(config-if)# end

3550(config)#

© 2002, Cisco Systems, Inc. All rights reserved

Cisco CCIE Prep v1.0—Module 5-42

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

Use the steps outlined in the following table to assign an Ethernet interface to a Layer 3 EtherChannel:

Table 4-24: Ethernet Interface

Command

Purpose

3550(config)# interface interface-id

Enters interface configuration mode and specifies a physical interface to configure. Only physical interfaces can be part of an Etherchannel.

Up to eight interfaces of the same type and speed can be configured for the same group.

3550(config-if)# no ip address

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

3550(config-if)# channel-group channel-group-number mode {auto [non-silent] | desirable [non-silent] | on}

Assigns the interface to a channel group, and specifies the PAgP mode (the default mode is auto silent).

For channel-group-number, the range is 1 to 64. This number must be the same as the port-channel-number (logical port) previously configured.

Each EtherChannel can consist of up to eight compatibly configured Ethernet interfaces.

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

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Fast Ethernet 1

Fast Ethernet 2

Fast Ethernet 3

Fast Ethernet 4

Fast EtherChannel

Fast EtherChannel

Fast Ethernet 4

Flow

Output Path

Flow

Output Path

F

A->D

FE 1

d->a

FE 4

B->D

FE 2

d->b

FE 3

C->D

FE 3

D->C

FE 1

etc.

FE ...

etc.

FE ...

stems, Inc. All rights re~

erved.

Cisco CCIE Prep vl.O—

Module 5-43

EtherChannel balances the traffic load across the bundled links based on the first two binary bits of a host's MAC address and/or IP address. EtherChannel load balancing can use either source-MAC or destination-MAC address forwarding.

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 (and the MAC address learned by the switch does not change).

When source-MAC address forwarding is used, load distribution based on the source and destination IP address is also enabled for routed IP traffic. All routed IP traffic chooses a port based on the source and destination IP address. Packets between two IP hosts always use the same port in the channel, and traffic between any other pair of hosts can use a different 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.

Use the steps outlined in the following table to configure EtherChannel load balancing:

Table 4-25: EtherChannel Load Balancing

Command

port-channel load-balance {dst-mac | src-mac}

Configures an EtherChannel load-balancing method:

■ dst-mac—Load distribution is based on the destination-host MAC address of the incoming packet. Packets to the same destination are sent on the same port, but packets to different destinations are sent on different ports in the channel.

src-mac—Load distribution is based on the source-MAC address of the incoming packet. Packets from different hosts use different ports in the channel, but packets from the same host use the same port in the channel. The default is src-mac

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

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