Link Dependency Concepts - NETGEAR M4200 Software Administration Manual

Link Dependency Concepts

Link dependency enables or disables ports in a group based on the link state of other ports in
the same group. That is, the link state of some ports depends on the link state of other ports.
For example, if port A depends on port B and the switch detects link loss on 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 specify whether link A is brought up or
brought down, depending on the state of link B. The ports that are participating in link
dependency can be among different members of a stack.
To establish link dependency, you must define a link state group. A link state group is
identified by a group number and consists of an upstream interface list, a downstream
interface list, and an action (up or down) that is associated with the group. One or more link
aggregation group (LAG) interfaces, one or more physical interfaces, or a combination of
both LAG interfaces and physical interfaces can be members of the upstream and
downstream interface list. If all the members of a link state group's upstream interface list go
down, all the downstream interfaces in the link state group are either brought down or
brought up, depending on the action that is associated with the group.
Note the following characteristics and limitations of link dependency:
• If you add an interface to the downstream list of a link state group, the interface remains
down until you add an upstream interface to the list. The link status of the downstream
interface is then determined by the link state of the upstream interface, as defined by the
action that is associated with the link state group. To prevent downstream interfaces from
remaining down in a link state group, configure upstream interfaces in the group before
you configure downstream interfaces in the group.
• If the configured action for a link group is up and if any configured upstream interface is
down, then upon configuring the downstream interfaces, all downstream interfaces are
immediately brought down.
• When a physical interface is configured as an upstream or downstream interface for a link
state group and you make the physical interface a member of a LAG interface, the
physical interface continues to be an upstream or downstream interface for the link state
group.
• An interface that is defined as an upstream interface in a link state group cannot be
defined as a downstream interface in the same link state group.
• Link dependencies cannot be circular. That is, an interface that is defined as an upstream
interface in one link state group cannot be defined as a downstream interface in another
link state group if such a configuration causes circular dependencies between groups.
Managed Switches
Link Dependency
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