Dell PowerConnect 8100 CLI Reference Guide - Page 613

Port Channels Trunking, which is also called Port Channels or Link Aggregation, is initiated and maintained by the periodic exchanges of Link Aggregation Control PDUs (LACPDUs). From a system perspective, a LAG is treated as a physical port. A LAG and a physical port use the same configuration parameters for administrative enable/disable, port priority, and path cost. When a physical port is configured as part of a LAG, it no longer participates in forwarding operations until the LAG becomes active. A LAG failure of one or more of the links stops traffic on the failed link. Upon failure, the flows mapped to a link are dynamically reassigned to the remaining links of the LAG. Similarly when links are added to a LAG, the conversations may need to be shifted to a new link. LAG Hashing The purpose of link aggregation is to increase bandwidth between two switches. It is achieved by aggregating multiple ports in one logical group. A common problem of port channels is the possibility of changing packets order in a particular TCP session. The resolution of this problem is correct selection of a physical port within the port channel for transmitting the packet to keep original packets order. The hashing algorithm is configurable for each LAG. Typically, an administrator is able to choose from hash algorithms utilizing the following attributes of a packet to determine the outgoing port: • Source MAC, VLAN, EtherType, and incoming port associated with the packet. • Source IP and Source TCP/UDP fields of the packet. • Destination MAC, VLAN, EtherType, and incoming port associated with the packet. • Source MAC, Destination MAC, VLAN, EtherType, and incoming port associated with the packet. • Destination IP and Destination TCP/UDP Port fields of the packet. • Source/Destination MAC, VLAN, EtherType, and incoming port associated with the packet. Port Channel Commands 613