Configuring Lacp Hot-Standby Ports; Configuring The Lacp System Priority - Cisco Catalyst 2960-XR Configuration Manual

Configuring LACP Hot-Standby Ports

Layer 2 EtherChannel Configuration Guidelines, on page 122
Configuring LACP Hot-Standby Ports
When enabled, LACP tries to configure the maximum number of LACP-compatible ports in a channel, up to
a maximum of 16 ports. Only eight LACP links can be active at one time. The software places any additional
links in a hot-standby mode. If one of the active links becomes inactive, a link that is in the hot-standby mode
becomes active in its place.
If you configure more than eight links for an EtherChannel group, the software automatically decides which
of the hot-standby ports to make active based on the LACP priority. To every link between systems that
operate LACP, the software assigns a unique priority made up of these elements (in priority order):
• LACP system priority
• System ID (the switch MAC address)
• LACP port priority
• Port number
In priority comparisons, numerically lower values have higher priority. The priority decides which ports
should be put in standby mode when there is a hardware limitation that prevents all compatible ports from
aggregating.
Determining which ports are active and which are hot standby is a two-step procedure. First the system with
a numerically lower system priority and system ID is placed in charge of the decision. Next, that system
decides which ports are active and which are hot standby, based on its values for port priority and port number.
The port priority and port number values for the other system are not used.
You can change the default values of the LACP system priority and the LACP port priority to affect how the
software selects active and standby links.

Configuring the LACP System Priority

You can configure the system priority for all the EtherChannels that are enabled for LACP by using the lacp
system-priority global configuration command. You cannot configure a system priority for each
LACP-configured channel. By changing this value from the default, you can affect how the software selects
active and standby links.
You can use the show etherchannel summary privileged EXEC command to see which ports are in the
hot-standby mode (denoted with an H port-state flag).
Beginning in privileged EXEC mode, follow these steps to configure the LACP system priority. This procedure
is optional.
SUMMARY STEPS
1. configure terminal
2. lacp system-priority priority
3. end
Catalyst 2960-XR Switch Layer 2 Configuration Guide, Cisco IOS Release 15.0(2)EX1
132
Configuring EtherChannels
OL-29424-01