Configuring an EtherChannel
Basically, for a Layer 3 EtherChannel, you should configure the logical
interface and then put the physical interfaces into the channel group:
(config)#interface port-channel number
(config-if)#no switchport
(config-if)#ip address address mask
Then, at each port that is part of the EtherChannel, use the following:
(config)#interface {number | range interface – interface}
(config-if)#channel-group number mode {auto | desirable | on}
Putting the IP address on the Port Channel interface creates a Layer 3
EtherChannel. Simply putting interfaces into a channel group creates a
Layer 2 EtherChannel, and the logical interface is automatically created.
The Cisco proprietary Port Aggregation Protocol (PAgP) dynamically
negotiates the formation of a channel. There are three PAgP modes:
■ On—The port channels without using PAgP negotiation. The port on
the other side must also be set to On.
■ Auto—Responds to PAgP messages but does not initiate them. Port
channels if the port on the other end is set to Desirable. This is the
default mode.
■ Desirable—Port actively negotiates channeling status with the interface
on the other end of the link. Port channels if the other side is Auto or
Desirable.
There is also a non-proprietary protocol called Link Aggregation Control
Protocol (LACP), IEEE 802.3ad, which does the same thing. LACP has two
modes:
■ Active—Port actively negotiates channeling with the port on the other
end of the link. A channel forms if the other side is Passive or Active.
■ Passive—Responds to LACP messages but does not initiate them. A
channel forms if the other end is set to Active.
If you want to use LACP, specify it under the interface and put the interface
in either active or passive mode:
(config-if)#channel-protocol lacp