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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 the figure below showing a three-port trunk, traffic could be assigned as shown in the following table.
Figure 17: Example: of port-trunked network
Table 15: Example: of link assignments in a trunk group (SA/DA distribution)
Source
Node A
Node B
Node C
Node D
Node A
Node B
Because the amount of traffic coming from or going to various nodes in a network can vary widely, it is possible
for one link in a trunk group to be fully utilized while other links in the same trunk have unused bandwidth capacity,
even if the assignments were evenly distributed across the links in a trunk.
Trunk load balancing using port layers
Trunk load balancing using port layers allows the use of TCP/UDP source and destination port number for trunk
load balancing. This is in addition to the current use of source and destination IP address and MAC addresses.
Configuration of Layer 4 load balancing would apply to all trunks on the switch. Only non-fragmented packets will
have their TCP/UDP port number used by load balancing. This ensures that all frames associated with a
fragmented IP packet are sent through the same trunk on the same physical link.
The priority for using layer packet information when this feature is enabled is as follows:
Procedure
1. L4-based: If the packet protocol is an IP packet, use Layer 4, or Layer 3, or Layer 2 information, whichever is
present, in that order.
2. L3-based: If the packet protocol is an IP packet, use Layer 3, or Layer 2 information, whichever is present, in
that order.
3. L2-based: If the packet protocol is an IP packet use Layer 2 information.
4. For all options, if the packet is not an IP packet, use Layer 2 information.
Enabling trunk load balancing
Enter the following command to enable load balancing.
Chapter 5 Port Trunking
Destination
Node W
Node X
Node Y
Node Z
Node Y
Node W
Link
1
2
3
1
2
3
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Troubleshooting
