Allied Telesis AT-S62 - Manual (Page 124)

Chapter 8: Port Trunking
Section I: Basic Operations 124
❑ Source IP Address (Layer 3)
❑ Destination IP Address (Layer 3)
❑ Source IP Address / Destination IP Address (Layer 3)
The load distribution methods can be divided into two general groups.
One group uses MAC addresses (Layer 2) to distribute the traffic and the
other uses IP addresses (Layer 3).
Source Address Distribution Methods
When a switch receives a packet from a network node, it examines the
destination address to determine on which switch port, if any, the
packet should be transmitted. If the packet is destined for a port trunk,
the switch then examines the source address of the packet. If this is the
first packet from the source node to be transmitted over a port trunk, the
switch assigns the source address to one of the trunk links.
Addresses are assigned to the ports of a trunk in a round-robin fashion. If
this is the first packet to be sent over the trunk, the source address is
assigned to the lowest numbered port in the trunk. All subsequent
packets from the source node are sent out the assigned data link of the
trunk.
When another node sends a packet over the trunk, its address is
assigned to the next lowest port in the trunk, and so forth. Once
addresses have been assigned to all the ports in the trunk, the process is
repeated starting with the lowest numbered port.
The goal of assigning addresses in this fashion is to try to evenly
distribute the addresses, or at least as much as possible, across all the
ports of the trunk, so as to ensure that all links in the trunk are utilized.
Figure 34 shows an example with two AT-8524M Series switches
interconnected with a port trunk of three data links. The trunk on Switch
#1 consists of ports 13 to 15 and on Switch #2 of ports 1 to 3. The
workstations are directing traffic to a server connected to Switch #2. The
server is connected to Switch #2 with a fiber optic Gigabit Ethernet data
link provided by an 1000Base fiber optic expansion module in Switch #2.