Specifications

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Catalyst 2970 Switch Software Configuration Guide
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Chapter 28 Configuring EtherChannels
Configuring EtherChannels
• Do not configure an EtherChannel in both the PAgP and LACP modes. EtherChannel groups
running PAgP and LACP can coexist on the same switch. Individual EtherChannel groups can run
either PAgP or LACP, but they cannot interoperate.
• Do not configure a Switched Port Analyzer (SPAN) destination as part of an EtherChannel.
• Do not configure a secure port as part of an EtherChannel or the reverse.
• Do not configure a port that is an active member of an EtherChannel as an 802.1X port. If 802.1X
is enabled on a not-yet active port of an EtherChannel, the port does not join the EtherChannel.
• For Layer 2 EtherChannels:
– Assign all interfaces in the EtherChannel to the same VLAN, or configure them as trunks.
Interfaces with different native VLANs cannot form an EtherChannel.
– If you configure an EtherChannel from trunk interfaces, verify that the trunking mode (ISL or
802.1Q) is the same on all the trunks. Inconsistent trunk modes on EtherChannel interfaces can
have unexpected results.
– 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 PAgP is set to the auto or desirable mode.
– Interfaces with different spanning-tree path costs can form an EtherChannel if they are
otherwise compatibly configured. Setting different spanning-tree path costs does not, by itself,
make interfaces incompatible for the formation of an EtherChannel.
Configuring Layer 2 EtherChannels
You configure Layer 2 EtherChannels by assigning interfaces to a channel group with the
channel-group interface configuration command. This command automatically creates the port-channel
logical interface.
Beginning in privileged EXEC mode, follow these steps to assign a Layer 2 Ethernet interface to a
Layer 2 EtherChannel. This procedure is required.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Enter interface configuration mode, and specify a physical
interface to configure.
Valid interfaces include physical interfaces.
For a PAgP EtherChannel, you can configure up to eight
interfaces of the same type and speed for the same group.
For a LACP EtherChannel, you can configure up to 16 Ethernet
interfaces of the same type. Up to eight ports can be active, and
up to eight ports can be in standby mode.
Step 3
switchport mode {access | trunk}
switchport access vlan vlan-id
Assign all interfaces as static-access ports in the same VLAN, or
configure them as trunks.
If you configure the interface as a static-access port, assign it to
only one VLAN. The range is 1 to 4094.