Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual page 149

Chapter 10 Configuring EtherChannels
Understanding Manual EtherChannel Configuration
Manually configured EtherChannel ports do not exchange EtherChannel protocol packets. A manually
configured EtherChannel forms only when you enter 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:
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Understanding IEEE 802.3ad LACP EtherChannel Configuration
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:
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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.
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 will initiate negotiation.
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
Understanding How EtherChannels Work
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