27-4
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 27 Configuring EtherChannel and Link State Tracking
About EtherChannel
•
When auto-LAG is disabled on a port interface that is already a part of an auto created EtherChannel,
the port interface will unbundle from the auto EtherChannel.
The following table shows the supported auto-LAG configurations between the actor and partner
devices:
On disabling auto-LAG globally, all auto created Etherchannels become manual EtherChannels.You
cannot add any configurations in an existing auto created EtherChannel. To add an new configuration,
convert the auto-created EtherChannel into a manual EtherChannel using the
port-channel
channel-number
persistent
command.
Note
Auto-LAG uses the LACP protocol to create an auto EtherChannel. Only one EtherChannel can be
automatically created with the unique partner devices.
Auto-LAG Configuration Guidelines
Follow these guidelines when configuring auto-LAG:
•
When auto-LAG is enabled globally and on the port interface, and you do not want the port interface
to become a member of the auto EtherChannel, disable the auto-LAG on the port interface.
•
A port interface does not bundle to an auto EtherChannel when it is already a member of a manual
EtherChannel. To allow it to bundle with the auto EtherChannel, first unbundle the manual
EtherChannel on the port interface.
•
When auto-LAG is enabled and an auto EtherChannel is created, you can create multiple
EtherChannels manually with the same partner device. But by default, the port tries to create auto
EtherChannel with the partner device.
•
Auto-LAG is supported only on Layer 2 EtherChannels. It is not supported on Layer 3 interfaces
and Layer 3 EtherChannels.
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:
Table 27-1
S
upported auto-LAG configuration on actor and partner devices
Actor/Partner Active
Passive
Auto
Active
Yes
Yes
Yes
Passive Yes
No
Yes
Auto
Yes
Yes
Yes
Summary of Contents for Catalyst 4500 Series
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