Configuration Guide User guide

718 FastIron Configuration Guide
53-1002494-02
Dynamic link aggregation
Dynamic link aggregation
Brocade software supports the IEEE 802.3ad standard for link aggregation. This standard
describes the Link Aggregation Control Protocol (LACP), a mechanism for allowing ports on both
sides of a redundant link to form a trunk link (aggregate link), without the need for manual
configuration of the ports into trunk groups.
When you enable link aggregation on a group of Brocade ports, the Brocade ports can negotiate
with the ports at the remote ends of the links to establish trunk groups.
The link aggregation feature automates trunk configuration but can coexist with the Brocade trunk
group feature. Link aggregation parameters do not interfere with trunk group parameters.
NOTE
Use the link aggregation feature only if the device at the other end of the link you want to aggregate
also supports IEEE 802.3ad link aggregation. Otherwise, you must manually configure the trunk
links.
Link aggregation support is disabled by default. You can enable the feature on an individual port
basis, in active or passive mode:
• Active mode – When you enable a port for active link aggregation, the Brocade port can
exchange standard LACP Data Unit (LACPDU) messages to negotiate trunk group configuration
with the port on the other side of the link. In addition, the Brocade port actively sends LACPDU
messages on the link to search for a link aggregation partner at the other end of the link, and
can initiate an LACPDU exchange to negotiate link aggregation parameters with an
appropriately configured remote port.
• Passive mode – When you enable a port for passive link aggregation, the Brocade port can
exchange LACPDU messages with the port at the remote end of the link, but the Brocade port
cannot search for a link aggregation port or initiate negotiation of an aggregate link. Thus, the
port at the remote end of the link must initiate the LACPDU exchange.
NOTE
Brocade recommends that you disable or remove the cables from the ports you plan to enable for
dynamic link aggregation. Doing so prevents the possibility that LACP will use a partial configuration
to talk to the other side of a link. A partial configuration does not cause errors, but does sometimes
require LACP to be disabled and re-enabled on both sides of the link to ensure that a full
configuration is used. It is easier to disable a port or remove its cable first. This applies both for
active link aggregation and passive link aggregation.
The following rules apply to units in an IronStack:
• With LACP trunk configurations, the LACP system ID is the MAC address of the Active Controller.
If the LACP system ID changes, the entire trunk flaps and an STP reconvergence occurs.
• Link aggregation can be used to form multi-slot aggregate links on stack units, but the link
aggregation keys must match for the port groups on each stack unit. For example, to configure
an aggregate link containing ports 1/1/1 through 1/1/4, and 3/1/5 through 3/1/8, you must
change the link aggregation key on one or both port groups so that the key is the same for all
eight ports. Refer to “IronStack LACP trunk group configuration example”.