36-3
Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter36 Configuring EtherChannels and Link-State Tracking
Understanding EtherChannels
The EtherChannel provides full-duplex bandwidth up to 800 Mb/s (Fast EtherChannel) or 8 Gb/s
(Gigabit EtherChannel) between your switch and another switch or host. Each EtherChannel can consist
of up to eight compatibly configured Ethernet ports.
All ports in each EtherChannel must be configured as either Layer2 or Layer 3 ports. The number of
EtherChannels is limited to 48. The EtherChannel Layer 3 ports are made up of routed ports. Routed
ports are physical ports configured to be in Layer 3 mode by using the no switchport interface
configuration command. For more information, see the Chapter12, “Configuring Interface
Characteristics.”
For more information, see the “EtherChannel Configuration Guidelines” section on page36-12.
You can configure an EtherChannel in one of these modes: Port Aggregation Protocol (PAgP), Link
Aggregation Control Protocol (LACP), or On. Configure both ends of the EtherChannel in the same
mode:
•When you configure one end of an EtherChannel in either PAgP or LACP mode, the system
negotiates with the other end of the channel to determine which ports should become active.
Incompatible ports are put into an independent state and continue to carry data traffic as would any
other single link. The port configuration does not change, but the port does not participate in the
EtherChannel.
•When you configure an EtherChannel in the on mode, no negotiations take place. The switch forces
all compatible ports to become active in the EtherChannel. The other end of the channel (on the other
switch) must also be configured in the on mode; otherwise, packet loss can occur.
You can create an EtherChannel on a standalone switch, on a single switch in the stack, or on multiple
switches in the stack (known as cross-stack EtherChannel). See Figure 36-2 and Figure 36-3.
If a link within an EtherChannel fails, traffic previously carried over that failed link moves to the
remaining links within the EtherChannel. If traps are enabled on the switch, a trap is sent for a failure
that identifies the switch, the EtherChannel, and the failed link. Inbound broadcast and multicast packets
on one link in an EtherChannel are blocked from returning on any other link of the EtherChannel.
Figure36-2 Single-Switch EtherChannel
Switch 1
Catalyst 3750 switch stack
Switch 2
Channel
group 1
Channel
group 2
StackWise
port
connections
Switch 3
Switch A
86492