HP ProCurve 9304M Installation And Configuration Manual page 185

Configuring Trunk Groups and Dynamic Link Aggregation
performance by enabling the optimization feature. The optimization feature uses a smaller session table, which
allows forwarding to occur more quickly.
NOTE: When you enable the server trunk load balancing optimization feature on a port, the feature listed above
are disabled on that port. This occurs because the features use the session table, but the optimization feature
uses a smaller session table than the other features. The configuration information for the other features is
retained in the device's configuration file, but the features are disabled.
Example of Server Trunk Load Balancing at Layer 3
Figure 7.6 shows an example of how IP traffic is load balanced to server trunk ports when the traffic is forwarded
at Layer 3. In this example, server trunk load balancing based on source and destination IP addresses is enabled
on a Gigabit Ethernet port connected to a network containing multiple clients. Four other Ethernet ports are
configured in a server trunk group that is connected to a multi-homed server. The server can have multiple
network adapters or a single adapter with multiple ports that have unique MAC and IP addresses.
Figure 7.6 Server trunk load balancing based on source and destination IP addresses
When the port connected to the client network receives traffic that needs to be forwarded to the server, the HP
device selects one of the ports in the trunk group, and forwards the traffic on the selected port.
The HP device selects the trunk port based on a hash value, which can be a number from 1 – 256. The HP device
calculates a hash value for traffic that enters the device through the server trunk load balancing port and exits the
device through a trunk group. The hash value is calculated based on the source and destination IP addresses in
the traffic.
After the HP device calculates the hash value for the traffic, the device examines the trunk ports connected to the
destination address and selects the port with the fewest hash values already assigned. After calculating a hash
value and assigning the value to a port, the device always uses the same port to forward traffic for the same
source and destination IP addresses.
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