Reference Guide

Stacking | 855
The stack continues to use the master’s chassis MAC address even after a failover. The MAC address is not
refreshed until the stack is reloaded and a different unit becomes the stack master.
Stacking LAG
When you use multiple links between stack units, Dell Networking OS automatically bundles them in a
stacking link aggregation group (LAG) to provide aggregated throughput and redundancy. The stacking
LAG is established automatically and transparently by Dell Networking OS (without user configuration)
after peering is detected and behaves as follows:
• The stacking LAG dynamically aggregates; it can lose link members or gain new links.
• Shortest path selection inside the stack: if multiple paths exist between two units in the stack, the
shortest path is used.
High Availability on S5000 Stacks
An S5000 stack has a master and standby management unit that provide redundancy in a similar way to
redundant Route Processor Modules (RPMs). As shown in Figure 48-3, the
show redundancy command
displays the current status and configuration of redundancy in the stack.
The master unit synchronizes the running configuration and protocol states so that the system fails over in
the event of a hardware or software fault on the master unit. In such an event, or when the master unit is
removed, the standby unit becomes the stack manager and Dell Networking OS elects a new standby unit.
Dell Networking OS resets the failed master unit: once online, it becomes a member unit; the remaining
members remain online.
Note: If a removed management unit is brought up as a standalone unit or as part of a different stack,
there is a possibility of MAC address collisions. If you add a standalone unit, which has the same priority as
the master stack unit, the standalone unit joins the stack as a member unit.