Friday, November 22, 2013

EtherChannel Guidelines


EtherChannel Configuration Guidelines

If improperly configured, some EtherChannel ports are automatically disabled to avoid network loops and other problems. Follow these guidelines to avoid configuration problems:
Do not try to configure more than 48 EtherChannels on the switch or switch stack.
Configure a PAgP EtherChannel with up to eight Ethernet ports of the same type.
Configure a LACP EtherChannel with up to16 Ethernet ports of the same type. Up to eight ports can be active, and up to eight ports can be in standby mode.
Configure all ports in an EtherChannel to operate at the same speeds and duplex modes.
Enable all ports in an EtherChannel. A port in an EtherChannel that is disabled by using the shutdown interface configuration command is treated as a link failure, and its traffic is transferred to one of the remaining ports in the EtherChannel.
When a group is first created, all ports follow the parameters set for the first port to be added to the group. If you change the configuration of one of these parameters, you must also make the changes to all ports in the group:
Allowed-VLAN list
Spanning-tree path cost for each VLAN
Spanning-tree port priority for each VLAN
Spanning-tree Port Fast setting
Do not configure a port to be a member of more than one EtherChannel group.
Do not configure an EtherChannel in both the PAgP and LACP modes. EtherChannel groups running PAgP and LACP can coexist on the same switch or on different switches in the stack. Individual EtherChannel groups can run either PAgP or LACP, but they cannot interoperate.
Do not configure a Switched Port Analyzer (SPAN) destination port as part of an EtherChannel.
Do not configure a secure port as part of an EtherChannel or the reverse.
Do not configure a private-VLAN port as part of an EtherChannel.
Do not configure a port that is an active or a not-yet-active member of an EtherChannel as an IEEE 802.1x port. If you try to enable IEEE 802.1x on an EtherChannel port, an error message appears, and IEEE 802.1x is not enabled.
If EtherChannels are configured on switch interfaces, remove the EtherChannel configuration from the interfaces before globally enabling IEEE 802.1x on a switch by using the dot1x system-auth-control global configuration command.

For Layer 2 EtherChannels:

Assign all ports in the EtherChannel to the same VLAN, or configure them as trunks. Ports with different native VLANs cannot form an EtherChannel.
If you configure an EtherChannel from trunk ports, verify that the trunking mode (ISL or IEEE 802.1Q) is the same on all the trunks. Inconsistent trunk modes on EtherChannel ports can have unexpected results.
An EtherChannel supports the same allowed range of VLANs on all the ports in a trunking Layer 2 EtherChannel. If the allowed range of VLANs is not the same, the ports do not form an EtherChannel even when PAgP is set to the auto or desirable mode.
Ports 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 ports incompatible for the formation of an EtherChannel.

For Layer 3 EtherChannels, assign the Layer 3 address to the port-channel logical interface, not to the physical ports in the channel.

Note Layer 3 EtherChannels are not supported on switches running the LAN base feature set.

For cross-stack EtherChannel configurations, ensure that all ports targeted for the EtherChannel are either configured for LACP or are manually configured to be in the channel group using the channel-group channel-group-number mode on interface configuration command. The PAgP protocol is not supported on cross- stack EtherChannels.
If cross-stack EtherChannel is configured and the switch stack partitions, loops and forwarding misbehaviors can occur. 

Default EtherChannel Configuration 

Channel groups
Port-channel logical interface
PAgP mode
PAgP learn method
Aggregate-port learning on all ports.
PAgP priority
128 on all ports.
LACP mode
LACP learn method
Aggregate-port learning on all ports.
LACP port priority
32768 on all ports.
LACP system priority
32768
LACP system ID
LACP system priority and the switch or stack MAC address.
Load-balancing
Load distribution on the switch is based on the source-MAC address of the incoming packet.


 Ref link : http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_53_se/configuration/guide/swethchl.html#wp1275881

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