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Auto-LAG overview
An Auto-LAG is a LAG that forms automatically between two devices that support the
Auto-LAG feature. An Auto-LAG is a dynamic Layer 2 LAG that is based on the Link
Aggregation Control Protocol (LACP).
Note: A LAG is also referred to as a port channel or an EtherChannel.
The switch can detect the physical links with a partner device and automatically configure
a LAG (that is, an Auto-LAG) on interconnected and capable ports at both ends. The
switch can form one Auto-LAG only with each partner device.
The Auto-LAG feature functions together with the Auto-Trunk feature, which must also
be supported and enabled on the partner device with which the LAG is formed. After
an Auto-LAG is formed, the switch automatically applies trunk mode (that is, an
Auto-Trunk) to the LAG at both ends. In other words, after an Auto-LAG is formed, the
mode for the ports that participate in an Auto-LAG changes from the default switch port
mode to the trunk port mode. For more information about the Auto-Trunk feature, see
Auto-Trunk overview on page 27.
For the switch to form an Auto-LAG with a partner switch, the following are required:
• Both the Auto-LAG and Auto-Trunk features must be supported and globally enabled
on the switch and the partner device.
(On all M4250 switch models, the Auto-LAG and Auto-Trunk features are enabled
by default.)
• At least two links must be established between the switch and the partner device,
and these links must support the same speed and duplex mode.
• The links cannot be members of a manually configured static or dynamic LAG.
• LLDP must be enabled on the interconnected ports on the switch and the partner
device.
(On all M4250 switch models, LLDP is enabled by default on all ports.)
• The interconnected ports on the switch and the partner device must be in the default
switch port mode, which is the General mode. If the ports are in the Access mode
or already in the Trunk mode, an Auto-Trunk cannot be formed on the Auto-LAG.
An Auto-LAG can form with up to eight interfaces as members. Interfaces are
automatically selected for the Auto-LAG based on whether they are up and available
and on the following conditions:
• The interface is not already manually configured as a member of a LAG.
• The interface is not manually configured as a trunk port or an access port. That is,
the interface must be a general interface.
Link Aggregation
AV Line of Fully Managed Switches M4250 Series
34
Audio Video User Manual
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