CLI Reference Guide

Port Channel Commands 591
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.
• Source/Destination IP and source/destination TCP/UDP Port fields of the
packet.
Enhanced LAG Hashing
Dell Networking devices based on Broadcom XGS-IV silicon support
configuration of hashing algorithms for each LAG interface. The hashing
algorithm is used to distribute traffic load among the physical ports of the
LAG while preserving the per-flow packet order.
One limitation with earlier LAG hashing techniques is that the packet
attributes were fixed for all type of packets. Also, there was no MODULO-N
operation involved, which can result in poor load balancing performance.
The LAG hashing support supports an enhanced hashing mode, which has
the following advantages:
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