The Trunk Hash Algorithm In order to distribute the load across all active ports in a trunk group, the following algorithm is used to determine which port within the trunk group to use for frame forwarding, where x is the number of active ports within the trunk group: (last 2 bytes SIP) xor (last 2 bytes DIP) xor (last 4 bytes SMAC) The values of parameters A and B are defined below for the different types of forwarding and frames. These two parameters are XORed together to give the hash index. The modulus (mod) x of the lower 6 bits of the hash index is then taken to give the port of the trunk group. Note: The same algorithm is used across all Alteons.
• For Layer 2 forwarding of non-IP frames:
A = lower 16 bits of destination MAC address
B = lower 32 bits of source MAC address • For Layer 2 forwarding of IP frames:
A = lower 16 bits of source IP address
B = lower 32 bits of source MAC address
• For Layer 3 forwarding (enabled in WSM platform and Cheetah 20.1):
A = lower 32 bits of destination IP
B = lower 16 bits of source MAC
• For Layer 4 trunking (traffic towards the real servers in SLB and WCR):
A = lower 32 bits of source IP
B = lower 16 bits of destination MAC