Users Guide

Stacking 239
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
stack master. 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