Dell POWEREDGE M1000E - Manual (Page 493)

Configuring Port Characteristics 493
What is Link Dependency?
The link dependency feature provides the ability to enable or disable one or
more ports based on the link state of one or more different ports. With link
dependency enabled on a port, the link state of that port is dependent on the
link state of another port. For example, if port A is dependent on port B and
the switch detects a link loss on port B, the switch automatically brings down
the link on port A. When the link is restored to port B, the switch
automatically restores the link to port A.
You can create a maximum of 72 dependency groups for stacking switches or
16 groups for a standalone switch. The ports participating in the Link
Dependency can be across all the Stack Units (Manager/Member unit).
Link Action
The link action specifies the action that the group members will take when
the dependent port is down. The group members can transition to the same
state as the dependant port, or they can transition to the opposite state. In
other words, if the link action is down and the dependent port goes down, the
members ports will go down as well. Conversely, when the link action is up
and the dependant link goes down, the group member ports are enabled
(brought up).
Creating a link dependency group with the up link action essentially creates a
backup link for the dependent link and alleviates the need to implement STP
to handle the fail-over.
Link Dependency Scenarios
The Link Dependency feature supports the scenarios in the following list.
• Port dependent on port — If a port loses the link, the switch brings
up/down the link on another port.
• Port dependent on LAG — If all ports in a channel-group lose the link, the
switch brings up/down the link on another port.
• LAG dependent on port — If a port loses the link, the switch brings
up/down all links in a channel-group.
NOTE: Whether the member ports or LAGs are brought up or down depends on
the link action.