12-3
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 12 Configuring EtherChannels
Understanding How EtherChannels Work
Understanding Manual EtherChannel Configuration
Manually configured EtherChannel ports do not exchange EtherChannel protocol packets. A manually
configured EtherChannel forms only when you configure all ports in the EtherChannel compatibly.
Understanding 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:
•
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 will initiate negotiation.
Table 12-1 EtherChannel Modes
Mode
Description
on
Mode that forces the LAN port to channel unconditionally. In the
on
mode, a usable
EtherChannel exists only when a LAN port group in the
on
mode is connected to another
LAN port group in the
on
mode. Because ports configured in the
on
mode do not negotiate,
there is no negotiation traffic between the ports. You cannot configure the
on
mode with
an EtherChannel protocol. If one end uses the
on
mode, the other end must also.
auto
PAgP mode that places a LAN port into a passive negotiating state, in which the port
responds to PAgP packets it receives but does not initiate PAgP negotiation. (Default)
desirable
PAgP mode that places a LAN port into an active negotiating state, in which the port
initiates negotiations with other LAN ports by sending PAgP packets.
passive
LACP mode that places a port into a passive negotiating state, in which the port responds
to LACP packets it receives but does not initiate LACP negotiation. (Default)
active
LACP mode that places a port into an active negotiating state, in which the port initiates
negotiations with other ports by sending LACP packets.
