Follow these guidelines and restrictions when configuring EtherChannel
interfaces:

-
EtherChannel Support – All Ethernet interfaces on all modules
support EtherChannel (maximum of eight interfaces), with no requirement that
interfaces be physically contiguous or on the same module.
-
Speed and Duplex – Configure all interfaces in an EtherChannel to
operate at the same speed and in the same duplex mode. Also, if one interface
in the bundle is shut down it is treated as a link failure and traffic will
traverse other links in the bundle.
-
SPAN and Etherchannel – An EtherChannel will not form if one of the
interfaces is a Switched Port Analyzer (SPAN) destination port.
-
For Layer 3 EtherChannels – Assign Layer 3 addresses to the
port-channel logical interface, not to the physical interfaces in the
channel.
-
VLAN match – All interfaces in the EtherChannel bundle must be
assigned to the same VLAN or be configured as a trunk
-
Range of VLANs – An EtherChannel supports the same allowed range of
VLANs on all the interfaces in a trunking Layer 2 EtherChannel. If the allowed
range of VLANs is not the same, the interfaces do not form an EtherChannel,
even when set to the auto or desirable mode. For Layer 2 EtherChannels, either
assign all interfaces in the EtherChannel to the same VLAN or configure them as
trunks.
-
STP Path Cost – Interfaces with different STP port path costs can
form an EtherChannel as long they are otherwise compatibly configured. Setting
different STP port path costs does not, by itself, make interfaces incompatible
for the formation of an EtherChannel.
-
Port Channel vs. Interface configuration – After configuring an
EtherChannel, any configuration you apply to the port-channel interface affects
the EtherChannel. Any configuration you apply to the physical interfaces
affects only the specific interface you configured.