23 LINK AGGREGATION CONFIGURATIONOverviewIntroduction to LinkAggregationLink aggregation aggregates multiple physical Ethernet ports into one logical link,also called an aggregation group. It allows you to increase bandwidth bydistributing incoming/outgoing traffic on the member ports in the aggregationgroup. In addition, it provides reliable connectivity because these member portscan dynamically back up each other.Depending on different aggregation modes, aggregation groups fall into threetypes: manual, static LACP, and dynamic LACP. Depending on whether or not loadsharing is implemented, aggregation groups can be load-sharing ornon-load-sharing aggregation groups.For the member ports in an aggregation group, their basic configuration must bethe same. The basic configuration includes STP, QoS, VLAN, port attributes andother associated settings.■ STP configuration, including STP status (enabled or disabled), link attribute(point-to-point or not), STP priority, maximum transmission speed, loopprevention status, root protection status, edge port or not.■ QoS configuration, including traffic limiting, priority marking, default 802.1ppriority, bandwidth assurance, congestion avoidance, traffic redirection, trafficstatistics, and so on.■ VLAN configuration, including permitted VLANs, and default VLAN ID.■ Port attribute configuration, including port rate, duplex mode, and link type(Trunk, Hybrid or Access). The ports for a manual or static aggregation groupmust have the same link type, and the ports for a dynamic aggregation groupmust have the same rate, duplex mode and link type.Introduction to LACP The purpose of the link aggregation control protocol (LACP) is to implementdynamic link aggregation and deaggregation. This protocol is defined inIEEE802.3ad. It uses link aggregation control protocol data units (LACPDUs) forinformation exchange between LACP-enabled devices.After LACP is enabled on a port, the port sends LACPDUs to notify the remotesystem of its system LACP priority, system MAC address, port LACP priority, portnumber, and operational key. Upon receipt of an LACPDU, the remote systemcompares the received information with the information received on other ports todetermine the ports that can operate as selected ports. This allows the twosystems to reach an agreement on the states of the related ports.
