Users Guide

Stacking 283
NSF in the Data Center
Figure 8-12 illustrates a data center scenario, where the stack of two Dell
EMC Networking N-Series switches acts as an access switch. The access
switch is connected to two aggregation switches, AS1 and AS2. The stack has
a link from two different units to each aggregation switch, with each pair of
links grouped together in a LAG. The two LAGs and link between AS1 and
AS2 are members of the same VLAN. Spanning tree is enabled on the VLAN.
Assume spanning tree selects AS1 as the root bridge. Assume the LAG to AS1
is the root port on the stack and the LAG to AS2 is discarding. Unit 1 is the
management unit in the stack. If unit 1 fails, the stack removes the Unit 1
link to AS1 from its LAG. The stack forwards outgoing packets through the
Unit 2 link to AS1 during the failover. During the failover, the stack continues
to send BPDUs and LAG PDUs on its links on Unit 2. The LAGs stay up
(with one remaining link in each), and spanning tree on the aggregation
switches does not see a topology change.
Figure 8-12. Data Center Stack Topology