27-5
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
•
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 initiates negotiation.
IEEE 802.3ad LACP EtherChannel Configuration
Cisco IOS Release 12.2(31)SGA 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 initiates 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
LACP System Priority and System ID” section on page 27-16
. 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
Layer 2 EtherChannels” section on page 27-11
. LACP uses the port priority with the port number to
form the port identifier.
•
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
Summary of Contents for Catalyst 4500 Series
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