104
“Disable” Port Role:
Disable LACP on specified port(s)
“Active” Port Role:
Active LACP ports are capable of processing and sending LACP control
frames. This allows LACP compliant devices to negotiate the aggregated link so that the group
may be changed dynamically as required. In order to utilize the ability to change an aggregated
port group, that is, to add or remove ports from the group, at least one of the participating devices
must designate LACP ports as active. Both devices must support LACP.
“Passive” Port Role:
LACP ports that are designated as passive cannot initially send LACP
control frames. In order to allow the linked port group to negotiate adjustments and make changes
dynamically, one end of the connection must have “active” LACP ports.
4.4.4 Rapid Spanning Tree
The Spanning Tree Protocol (STP), defined in the IEEE Standard 802.1D, creates a spanning tree
within a mesh network of connected layer-2 bridges (typically Ethernet switches) and disables the
links which are not part of that tree, leaving a single active path between any two network nodes.
Multiple active paths between network nodes cause a bridge loop. Bridge loops create several
problems. First, the MAC address table used by the switch or bridge can fail, since the same MAC
addresses (and hence the same network hosts) are seen on multiple ports. Second, a broadcast
storm occurs. This is caused by broadcast packets being forwarded in an endless loop between
switches. A broadcast storm can consume all available CPU resources and bandwidth.
Spanning tree allows a network design to include spare (redundant) links to provide automatic
backup paths if an active link fails, without the danger of bridge loops, or the need for manually
enabling/disabling these backup links.
To provide faster spanning tree convergence after a topology change, an evolution of the
Spanning Tree Protocol: Rapid Spanning Tree Protocol (RSTP), introduced by IEEE with
document 802.1w. RSTP, is a refinement of STP; therefore, it shares most of its basic operation
characteristics. This essentially creates a cascading effect away from the root bridge where each
