KB.15.15

Figure 61 A dynamic LACP trunk forming in a VLAN can cause a traffic loop

Easy control methods include either disabling LACP on the selected ports or configuring them to

operate in static LACP trunks.

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.

Trunk group operation using the "trunk" option 157