Vlan And Trunk Configuration Guidelines; Interaction With Other Features Guidelines - Cisco WS-C6506 Software Manual

EtherChannel Configuration Guidelines
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VLAN and Trunk Configuration Guidelines

This section describes the guidelines for VLAN and trunk-related configuration:
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Interaction with Other Features Guidelines

This section describes the guidelines for the EtherChannel's interaction with other features:
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
6-4
You can change the protocol at any time, but this change causes all existing EtherChannels to reset to the
default channel mode for the new protocol.
Configure all ports in an EtherChannel to operate at the same speed and duplex mode (full duplex
only for LACP mode).
Enable all ports in an EtherChannel. If you disable a port in an EtherChannel, it is treated as a link
failure and its traffic is transferred to one of the remaining ports in the EtherChannel.
A port cannot belong to more than one channel group at the same time.
Ports with different port path costs, set by the set spantree portcost command, can form an
EtherChannel as long as they are otherwise compatibly configured. Setting different port path costs
does not, by itself, make ports incompatible for the formation of an EtherChannel.
PAgP and LACP manage channels differently. When all the ports in a channel get disabled, PAgP
removes them from its internal channels list; the show commands do not display the channel. With
LACP, when all the ports in a channel get disabled, LACP does not remove the channel; the show
commands continue to display the channel even though all its ports are down. To determine if a
channel is actively sending and receiving traffic with LACP, enter the show port command to see if
the link is up or down.
LACP does not support half-duplex links. If a port is in active/passive mode and becomes half
duplex, the port is suspended (and a syslog message is generated). The port is shown as "connected"
when you enter the show port command and as "not connected" when you enter the show spantree
command. This discrepancy occurs because the port is physically connected but never joined
spanning tree. To get the port to join spanning tree, either set the duplex to full or set the channel
mode to off for that port.
With software release 7.3(1) and later releases, the LACP behavior for the half-duplex links has
changed and the affected ports are no longer suspended. Instead of suspending a port, the LACP
PDU transmission (if any) is suppressed. If the port is part of a channel, the port is detached from
the channel but still functions as a nonchannel port. A syslog message is generated when this
condition occurs. The normal LACP behavior is reenabled automatically when you set the link to
full duplex.
Assign all ports in an EtherChannel to the same VLAN, or configure them as trunk ports.
If you configure the EtherChannel as a trunk, configure the same trunk mode on all the ports in the
EtherChannel. Configuring ports in an EtherChannel in different trunk modes can have unexpected
results.
An EtherChannel supports the same allowed range of VLANs on all the ports in a trunking
EtherChannel. If the allowed range of VLANs is not the same for a port list, the ports do not form
an EtherChannel even when set to the auto or desirable mode with the set port channel command.
Do not configure the ports in an EtherChannel as dynamic VLAN ports. Doing so can adversely
affect switch performance.
Ports with different VLAN cost configurations cannot form a channel.
Chapter 6 Configuring EtherChannel
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