Spanning Tree and IGMP
If Spanning Tree, IGMP, or both are enabled in the switch, a dynamic LACP trunk operates only with the default
settings for these features and does not appear in the port listings for these features.
Half-duplex, different port speeds, or both not allowed in LACP trunks
Theports on both sides of an LACP trunk must be configured for the same speed and for full-duplex (FDx). The
802.3ad LACP standard specifies a full-duplex (FDx) requirement for LACP trunking. (10-gigabit ports operate
only at FDx.)
A port configured as LACP passive and not assigned to a port trunk can be configured to half-duplex (HDx).
However, in any of the following cases, a port cannot be reconfigured to an HDx setting:
• If the port is a 10-gigabit port.
• If a port is set to LACP Active, you cannot configure it to HDx.
• If a port is already a member of a static or dynamic LACP trunk, you cannot configure it to HDx.
• If a port is already set to HDx, the switch does not allow you to configure it for a static or dynamic LACP trunk.
Dynamic/static LACP interoperation
A port configured for dynamic LACP can properly interoperate with a port configured for static (TrkX) LACP, but
any ports configured as standby LACP links are ignored.
Trunk group operation using the "trunk" option
This method creates a trunk group that operates independently of specific trunking protocols and does not use a
protocol exchange with the device on the other end of the trunk. With this choice, the switch simply uses the
SA/DA method of distributing outbound traffic across the trunked ports without regard for how that traffic is
handled by the device at the other end of the trunked links. Similarly, the switch handles incoming traffic from the
trunked links as if it were from a trunked source.
When a trunk group is configured with the
trunk
option, the switch automatically sets the trunk to a priority of "4"
for Spanning Tree operation (even if Spanning Tree is currently disabled). This appears in the running-config file
as
spanning-tree Trkn priority 4
. Executing
write memory
after configuring the trunk places the same
entry in the startup-config file.
Use the
trunk
option to establish a trunk group between a switch and another device, where the other device's
trunking operation fails to operate properly with LACP trunking configured on the switches.
How the switch lists trunk data
Static trunk group
Appears in the menu interface and the output from the CLI
show trunk
and
show interfaces
commands.
Dynamic LACP trunk group
Appears in the output from the CLI
show lacp
command.
Chapter 5 Port Trunking
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