Specifications

Link Aggregation Control Protocol (LACP)
LACP Operation
SecureStack B2 Configuration Guide 3-33
3.5 LINK AGGREGATION CONTROL PROTOCOL (LACP)
Using multiple links simultaneously to increase bandwidth is a desirable switch feature, which can
be accomplished if both sides agree on a set of ports that are being used as a Link Aggregation
Group (LAG). Once a LAG is formed from selected ports, problems with looping can be avoided
since the Spanning Tree can treat this LAG as a single port.
The Link Aggregation Control Protocol (LACP) logically groups interfaces together to create a
greater bandwidth uplink, or link aggregation, according to the IEEE 802.3ad standard. This
standard allows the switch to determine which ports are in LAGs and configure them dynamically.
Since the protocol is based on the IEEE 802.3ad specification, any switch from any vendor that
supports this standard can aggregate links automatically.
802.3ad LACP aggregations can also be run to end-users (ie; a server) or to a router.
3.5.1 LACP Operation
For each aggregatable port in the device, LACP:
• Maintains configuration information (reflecting the inherent properties of the individual links as
well as those established by management) to control aggregation.
• Exchanges configuration information with other devices to allocate the link to a Link
Aggregation Group (LAG).
• Attaches the port to the aggregator used by the LAG, and detaches the port from the aggregator
when it is no longer used by the LAG.
CAUTION: Link aggregation configuration should only be performed by personnel who are
knowledgeable about Spanning Tree and Link Aggregation, and fully understand the
ramifications of modifications beyond device defaults. Otherwise, the proper operation of the
network could be at risk.
NOTE: Earlier (proprietary) implementations of port aggregation referred to groups of
aggregated ports as "trunks".
NOTE: A given link is allocated to, at most, one Link Aggregation Group (LAG) at a time. The
allocation mechanism attempts to maximize aggregation, subject to management controls.