Chapter 4: Trunking
Trunking Overview
Trunking Guidelines
Trunking Algorithm
A port trunk is an economical way for you to increase the bandwidth between the Ethernet switch and another networking device, such as a network server, router, workstation, or another Ethernet switch. A port trunk is a group of ports that have been grouped together to function as one logical path. A port trunk, therefore, increases the bandwidth between the switch and the other network device and is useful in situations where a single physical link between the devices is insufficient to handle the traffic load. The
Because network vendors employ different techniques to implement trunking, a trunk on one device might not be compatible with the same feature on a device from another manufacturer. Therefore, trunks are typically made only between devices from the same vendor.
If a port in a static trunk loses its link, the trunk’s total bandwidth is reduced until the lost link is reconfigured.
The following are guidelines for setting up trunking:
To ensure compatibility, set up trunks only between
The trunk always contains two ports, one of which is designated the master port.
The
Before you create a trunk, examine the speed, duplex mode, and flow control settings of all the ports that will be in the trunk. Verify that the port settings are identical.
After you create a trunk, do not change the speed, duplex mode, or flow control setting of any port in the trunk without making the same changes to the other ports.
The ports of the trunk must be members of the same VLAN.
The switch selects the lowest numbered port in the trunk to handle broadcast packets and packets of unknown destination. For example, in trunk 2 containing ports 3 and 4, port 3 is used for broadcast packets.
One of the steps in creating a trunk is the selection of a load distribution method, also known as the trunking (or load distribution) algorithm. This algorithm determines how the switch distributes the traffic load across the ports of the trunk. The
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