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Understanding How EtherChannel Works
Understanding How EtherChannel Works
EtherChannel aggregates the bandwidth of up to eight compatibly configured ports into a single logical
link. Catalyst 6500 series switches support a maximum of 128 EtherChannels. All Ethernet ports on all
modules, including those on a standby supervisor engine, support EtherChannel with no requirement that
ports be contiguous or on the same module. All ports in each EtherChannel must be the same speed.
With software release 6.3(1) and later releases, due to the port ID handling by the spanning-tree feature,
Note
the maximum supported number of EtherChannels is 126 for a 6- or 9-slot chassis and 63 for a 13-slot
chassis.
The network device to which a Catalyst 6500 series switch is connected may impose its own limits on
Note
the number of ports in an EtherChannel.
If a link within an EtherChannel fails, the traffic that was previously carried over the failed link switches
to the remaining links within the EtherChannel. Inbound broadcast and multicast packets on one link in
an EtherChannel are blocked from returning on any other link of the EtherChannel.
You can configure EtherChannels as trunks. After a channel is formed, configuring any port in the
channel as a trunk applies the configuration to all ports in the channel. Identically configured trunk ports
can be configured as an EtherChannel.
Understanding How EtherChannel Frame Distribution Works
EtherChannel distributes frames across the links in a channel by reducing part of the binary pattern
formed from the addresses in the frame to a numerical value that selects one of the links in the channel.
EtherChannel frame distribution is based on a Cisco-proprietary hashing algorithm. The algorithm is
deterministic; given the same addresses and session information, you always hash to the same port in the
channel, preventing out-of-order packet delivery.
The address may be a source, a destination, or a combination of two IP addresses, two MAC addresses,
or two TCP/UDP port numbers depending on the policy that is adopted through the ip, mac, session, and
ip-vlan-session options of the set port channel all distribution command. See the
EtherChannel Load Balancing" section on page 6-11
The set port channel all distribution session command is supported on Supervisor Engine 2,
Note
Supervisor Engine 720, and Supervisor Engine 32 only. The set port channel all distribution
ip-vlan-session command is supported on Supervisor Engine 720 and Supervisor Engine 32 only.
EtherChannel frame distribution is not configurable on all supervisor engines. Enter the show module
command on a supervisor engine to determine if EtherChannel frame distribution is configurable on your
switch. If the display shows the "Sub-Type" to be "L2 Switching Engine I WS-F6020," then
EtherChannel frame distribution is not configurable on your Catalyst 6500 series switch; the switch uses
source and destination Media Access Control (MAC) addresses.
EtherChannel frame distribution is configurable with all other switching engines. The default is to use
source and destination IP addresses.
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
6-2
Chapter 6
for detailed information.
Configuring EtherChannel
"Configuring
OL-8978-04
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