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6 LINK AGGREGATION
You can create multiple links between devices that work as one virtual,
aggregate link. A port trunk offers a dramatic increase in bandwidth for
network segments where bottlenecks exist, as well as providing a fault-
tolerant link between two switches.
This chapter includes the following sections for configuring link
aggregation:
◆ “General Link Aggregation Guidelines” on page 49
◆ “Creating Trunk Groups” on page 50
◆ “Configuring Trunk Settings” on page 52
◆ “Configuring LACP” on page 54
GENERAL LINK AGGREGATION GUIDELINES
The switch supports both static trunking and dynamic Link Aggregation
Control Protocol (LACP). Static trunks have to be manually configured at
both ends of the link, and the switches must comply with the Cisco
EtherChannel standard. On the other hand, LACP configured ports can
automatically negotiate a trunked link with LACP-configured ports on
another device. You can configure any number of ports on the switch to use
LACP, as long as they are not already configured as part of a static trunk. If
ports on another device are also configured to use LACP, the switch and the
other device will negotiate a trunk between them. If an LACP trunk consists
of more than eight ports, all other ports will be placed in standby mode.
Should one link in the trunk fail, one of the standby ports will automatically
be activated to replace it.
Besides balancing the load across each port in the trunk, the other ports
provide redundancy by taking over the load if a port in the trunk fails.
However, before making any physical connections between devices,
configure the trunk on the devices at both ends. When using a port trunk,
take note of the following points:
◆ Finish configuring port trunks before you connect the corresponding
network cables between switches to avoid creating a loop.
◆ You can create up to 8 trunks on a switch, with up to 8 ports per trunk.
◆ The ports at both ends of a connection must be configured as trunk
ports.
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