HP 6120XG ProCurve Series 6120 Blade Switches Management and Configuration Gui - Page 280

Port Trunking Outbound Traffic Distribution Across Trunked Links The load-balancing is done on a per communication basis. Otherwise, traffic is transmitted across the same path as shown in figure 11-13. That is, if Client A attached to Switch 1 sends five packets of data to Server A attached to Switch 2, the same link is used to send all five packets. The SA/DA address pair for the traffic is the same. The packets are not evenly distributed across any other existing links between the two switches; they all take the same path. Client A All five packets go through the same link Client B Switch 1 Switch 2 Figure 11-13. Example of Single Path Traffic through a Trunk The actual distribution of the traffic through a trunk depends on a calculation using bits from the Source Address and Destination address. When an IP address is available, the calculation includes the last five bits of the IP source address and IP destination address, otherwise the MAC addresses are used. The result of that process undergoes a mapping that determines which link the traffic goes through. If you have only two ports in a trunk, it is possible that all the traffic will be sent through one port even if the SA/DA pairs are different. The more ports you have in the trunk, the more likely it is that the traffic will be distributed among the links. When a new port is added to the trunk, the switch begins sending traffic, either new traffic or existing traffic, through the new link. As links are added or deleted, the switch redistributes traffic across the trunk group. For example, in figure 11-14 showing a three-port trunk, traffic could be assigned as shown in table 11-6. A C1 B C Switch C2 C3 D W Switch X Y Z Figure 11-14. Example of Port-Trunked Network 11-28